"use strict";

var to_ascii = typeof atob == "undefined" ? function(b64) {
    return new Buffer(b64, "base64").toString();
} : atob;
var to_base64 = typeof btoa == "undefined" ? function(str) {
    return new Buffer(str).toString("base64");
} : btoa;

function read_source_map(code) {
    var match = /\n\/\/# sourceMappingURL=data:application\/json(;.*?)?;base64,(.*)/.exec(code);
    if (!match) {
        AST_Node.warn("inline source map not found");
        return null;
    }
    return to_ascii(match[2]);
}

function set_shorthand(name, options, keys) {
    if (options[name]) {
        keys.forEach(function(key) {
            if (options[key]) {
                if (typeof options[key] != "object") options[key] = {};
                if (!(name in options[key])) options[key][name] = options[name];
            }
        });
    }
}

function init_cache(cache) {
    if (!cache) return;
    if (!("props" in cache)) {
        cache.props = new Dictionary();
    } else if (!(cache.props instanceof Dictionary)) {
        cache.props = Dictionary.fromObject(cache.props);
    }
}

function to_json(cache) {
    return {
        props: cache.props.toObject()
    };
}

function minify(files, options) {
    var warn_function = AST_Node.warn_function;
    try {
        options = defaults(options, {
            compress: {},
            ecma: undefined,
            ie8: false,
            keep_classnames: undefined,
            keep_fnames: false,
            mangle: {},
            nameCache: null,
            output: {},
            parse: {},
            rename: undefined,
            safari10: false,
            sourceMap: false,
            timings: false,
            toplevel: false,
            warnings: false,
            wrap: false,
        }, true);
        var timings = options.timings && {
            start: Date.now()
        };
        if (options.keep_classnames === undefined) {
            options.keep_classnames = options.keep_fnames;
        }
        if (options.rename === undefined) {
            options.rename = options.compress && options.mangle;
        }
        set_shorthand("ecma", options, [ "parse", "compress", "output" ]);
        set_shorthand("ie8", options, [ "compress", "mangle", "output" ]);
        set_shorthand("keep_classnames", options, [ "compress", "mangle" ]);
        set_shorthand("keep_fnames", options, [ "compress", "mangle" ]);
        set_shorthand("safari10", options, [ "mangle", "output" ]);
        set_shorthand("toplevel", options, [ "compress", "mangle" ]);
        set_shorthand("warnings", options, [ "compress" ]);
        var quoted_props;
        if (options.mangle) {
            options.mangle = defaults(options.mangle, {
                cache: options.nameCache && (options.nameCache.vars || {}),
                eval: false,
                ie8: false,
                keep_classnames: false,
                keep_fnames: false,
                properties: false,
                reserved: [],
                safari10: false,
                toplevel: false,
            }, true);
            if (options.mangle.properties) {
                if (typeof options.mangle.properties != "object") {
                    options.mangle.properties = {};
                }
                if (options.mangle.properties.keep_quoted) {
                    quoted_props = options.mangle.properties.reserved;
                    if (!Array.isArray(quoted_props)) quoted_props = [];
                    options.mangle.properties.reserved = quoted_props;
                }
                if (options.nameCache && !("cache" in options.mangle.properties)) {
                    options.mangle.properties.cache = options.nameCache.props || {};
                }
            }
            init_cache(options.mangle.cache);
            init_cache(options.mangle.properties.cache);
        }
        if (options.sourceMap) {
            options.sourceMap = defaults(options.sourceMap, {
                content: null,
                filename: null,
                includeSources: false,
                root: null,
                url: null,
            }, true);
        }
        var warnings = [];
        if (options.warnings && !AST_Node.warn_function) {
            AST_Node.warn_function = function(warning) {
                warnings.push(warning);
            };
        }
        if (timings) timings.parse = Date.now();
        var toplevel;
        if (files instanceof AST_Toplevel) {
            toplevel = files;
        } else {
            if (typeof files == "string") {
                files = [ files ];
            }
            options.parse = options.parse || {};
            options.parse.toplevel = null;
            for (var name in files) if (HOP(files, name)) {
                options.parse.filename = name;
                options.parse.toplevel = parse(files[name], options.parse);
                if (options.sourceMap && options.sourceMap.content == "inline") {
                    if (Object.keys(files).length > 1)
                        throw new Error("inline source map only works with singular input");
                    options.sourceMap.content = read_source_map(files[name]);
                }
            }
            toplevel = options.parse.toplevel;
        }
        if (quoted_props) {
            reserve_quoted_keys(toplevel, quoted_props);
        }
        if (options.wrap) {
            toplevel = toplevel.wrap_commonjs(options.wrap);
        }
        if (timings) timings.rename = Date.now();
        // disable rename on harmony due to expand_names bug in for-of loops
        // https://github.com/mishoo/UglifyJS2/issues/2794
        if (0 && options.rename) {
            toplevel.figure_out_scope(options.mangle);
            toplevel.expand_names(options.mangle);
        }
        if (timings) timings.compress = Date.now();
        if (options.compress) toplevel = new Compressor(options.compress).compress(toplevel);
        if (timings) timings.scope = Date.now();
        if (options.mangle) toplevel.figure_out_scope(options.mangle);
        if (timings) timings.mangle = Date.now();
        if (options.mangle) {
            base54.reset();
            toplevel.compute_char_frequency(options.mangle);
            toplevel.mangle_names(options.mangle);
        }
        if (timings) timings.properties = Date.now();
        if (options.mangle && options.mangle.properties) {
            toplevel = mangle_properties(toplevel, options.mangle.properties);
        }
        if (timings) timings.output = Date.now();
        var result = {};
        if (options.output.ast) {
            result.ast = toplevel;
        }
        if (!HOP(options.output, "code") || options.output.code) {
            if (options.sourceMap) {
                if (typeof options.sourceMap.content == "string") {
                    options.sourceMap.content = JSON.parse(options.sourceMap.content);
                }
                options.output.source_map = SourceMap({
                    file: options.sourceMap.filename,
                    orig: options.sourceMap.content,
                    root: options.sourceMap.root
                });
                if (options.sourceMap.includeSources) {
                    if (files instanceof AST_Toplevel) {
                        throw new Error("original source content unavailable");
                    } else for (var name in files) if (HOP(files, name)) {
                        options.output.source_map.get().setSourceContent(name, files[name]);
                    }
                }
            }
            delete options.output.ast;
            delete options.output.code;
            var stream = OutputStream(options.output);
            toplevel.print(stream);
            result.code = stream.get();
            if (options.sourceMap) {
                result.map = options.output.source_map.toString();
                if (options.sourceMap.url == "inline") {
                    result.code += "\n//# sourceMappingURL=data:application/json;charset=utf-8;base64," + to_base64(result.map);
                } else if (options.sourceMap.url) {
                    result.code += "\n//# sourceMappingURL=" + options.sourceMap.url;
                }
            }
        }
        if (options.nameCache && options.mangle) {
            if (options.mangle.cache) options.nameCache.vars = to_json(options.mangle.cache);
            if (options.mangle.properties && options.mangle.properties.cache) {
                options.nameCache.props = to_json(options.mangle.properties.cache);
            }
        }
        if (timings) {
            timings.end = Date.now();
            result.timings = {
                parse: 1e-3 * (timings.rename - timings.parse),
                rename: 1e-3 * (timings.compress - timings.rename),
                compress: 1e-3 * (timings.scope - timings.compress),
                scope: 1e-3 * (timings.mangle - timings.scope),
                mangle: 1e-3 * (timings.properties - timings.mangle),
                properties: 1e-3 * (timings.output - timings.properties),
                output: 1e-3 * (timings.end - timings.output),
                total: 1e-3 * (timings.end - timings.start)
            }
        }
        if (warnings.length) {
            result.warnings = warnings;
        }
        return result;
    } catch (ex) {
        return { error: ex };
    } finally {
        AST_Node.warn_function = warn_function;
    }
}

/***********************************************************************

  A JavaScript tokenizer / parser / beautifier / compressor.
  https://github.com/mishoo/UglifyJS2

  -------------------------------- (C) ---------------------------------

                           Author: Mihai Bazon
                         <mihai.bazon@gmail.com>
                       http://mihai.bazon.net/blog

  Distributed under the BSD license:

    Copyright 2012 (c) Mihai Bazon <mihai.bazon@gmail.com>

    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions
    are met:

        * Redistributions of source code must retain the above
          copyright notice, this list of conditions and the following
          disclaimer.

        * Redistributions in binary form must reproduce the above
          copyright notice, this list of conditions and the following
          disclaimer in the documentation and/or other materials
          provided with the distribution.

    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER “AS IS” AND ANY
    EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
    IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
    PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER BE
    LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY,
    OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
    PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
    PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
    THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR
    TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
    THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
    SUCH DAMAGE.

 ***********************************************************************/

"use strict";

function characters(str) {
    return str.split("");
};

function member(name, array) {
    return array.indexOf(name) >= 0;
};

function find_if(func, array) {
    for (var i = 0, n = array.length; i < n; ++i) {
        if (func(array[i]))
            return array[i];
    }
};

function repeat_string(str, i) {
    if (i <= 0) return "";
    if (i == 1) return str;
    var d = repeat_string(str, i >> 1);
    d += d;
    if (i & 1) d += str;
    return d;
};

function configure_error_stack(fn) {
    Object.defineProperty(fn.prototype, "stack", {
        get: function() {
            var err = new Error(this.message);
            err.name = this.name;
            try {
                throw err;
            } catch(e) {
                return e.stack;
            }
        }
    });
}

function DefaultsError(msg, defs) {
    this.message = msg;
    this.defs = defs;
};
DefaultsError.prototype = Object.create(Error.prototype);
DefaultsError.prototype.constructor = DefaultsError;
DefaultsError.prototype.name = "DefaultsError";
configure_error_stack(DefaultsError);

DefaultsError.croak = function(msg, defs) {
    throw new DefaultsError(msg, defs);
};

function defaults(args, defs, croak) {
    if (args === true)
        args = {};
    var ret = args || {};
    if (croak) for (var i in ret) if (HOP(ret, i) && !HOP(defs, i))
        DefaultsError.croak("`" + i + "` is not a supported option", defs);
    for (var i in defs) if (HOP(defs, i)) {
        ret[i] = (args && HOP(args, i)) ? args[i] : defs[i];
    }
    return ret;
};

function merge(obj, ext) {
    var count = 0;
    for (var i in ext) if (HOP(ext, i)) {
        obj[i] = ext[i];
        count++;
    }
    return count;
};

function noop() {}
function return_false() { return false; }
function return_true() { return true; }
function return_this() { return this; }
function return_null() { return null; }

var MAP = (function(){
    function MAP(a, f, backwards) {
        var ret = [], top = [], i;
        function doit() {
            var val = f(a[i], i);
            var is_last = val instanceof Last;
            if (is_last) val = val.v;
            if (val instanceof AtTop) {
                val = val.v;
                if (val instanceof Splice) {
                    top.push.apply(top, backwards ? val.v.slice().reverse() : val.v);
                } else {
                    top.push(val);
                }
            }
            else if (val !== skip) {
                if (val instanceof Splice) {
                    ret.push.apply(ret, backwards ? val.v.slice().reverse() : val.v);
                } else {
                    ret.push(val);
                }
            }
            return is_last;
        };
        if (a instanceof Array) {
            if (backwards) {
                for (i = a.length; --i >= 0;) if (doit()) break;
                ret.reverse();
                top.reverse();
            } else {
                for (i = 0; i < a.length; ++i) if (doit()) break;
            }
        }
        else {
            for (i in a) if (HOP(a, i)) if (doit()) break;
        }
        return top.concat(ret);
    };
    MAP.at_top = function(val) { return new AtTop(val) };
    MAP.splice = function(val) { return new Splice(val) };
    MAP.last = function(val) { return new Last(val) };
    var skip = MAP.skip = {};
    function AtTop(val) { this.v = val };
    function Splice(val) { this.v = val };
    function Last(val) { this.v = val };
    return MAP;
})();

function push_uniq(array, el) {
    if (array.indexOf(el) < 0)
        array.push(el);
};

function string_template(text, props) {
    return text.replace(/\{(.+?)\}/g, function(str, p){
        return props && props[p];
    });
};

function remove(array, el) {
    for (var i = array.length; --i >= 0;) {
        if (array[i] === el) array.splice(i, 1);
    }
};

function mergeSort(array, cmp) {
    if (array.length < 2) return array.slice();
    function merge(a, b) {
        var r = [], ai = 0, bi = 0, i = 0;
        while (ai < a.length && bi < b.length) {
            cmp(a[ai], b[bi]) <= 0
                ? r[i++] = a[ai++]
                : r[i++] = b[bi++];
        }
        if (ai < a.length) r.push.apply(r, a.slice(ai));
        if (bi < b.length) r.push.apply(r, b.slice(bi));
        return r;
    };
    function _ms(a) {
        if (a.length <= 1)
            return a;
        var m = Math.floor(a.length / 2), left = a.slice(0, m), right = a.slice(m);
        left = _ms(left);
        right = _ms(right);
        return merge(left, right);
    };
    return _ms(array);
};

// this function is taken from Acorn [1], written by Marijn Haverbeke
// [1] https://github.com/marijnh/acorn
function makePredicate(words) {
    if (!(words instanceof Array)) words = words.split(" ");
    var f = "", cats = [];
    out: for (var i = 0; i < words.length; ++i) {
        for (var j = 0; j < cats.length; ++j)
            if (cats[j][0].length == words[i].length) {
                cats[j].push(words[i]);
                continue out;
            }
        cats.push([words[i]]);
    }
    function quote(word) {
        return JSON.stringify(word).replace(/[\u2028\u2029]/g, function(s) {
            switch (s) {
                case "\u2028": return "\\u2028";
                case "\u2029": return "\\u2029";
            }
            return s;
        });
    }
    function compareTo(arr) {
        if (arr.length == 1) return f += "return str === " + quote(arr[0]) + ";";
        f += "switch(str){";
        for (var i = 0; i < arr.length; ++i) f += "case " + quote(arr[i]) + ":";
        f += "return true}return false;";
    }
    // When there are more than three length categories, an outer
    // switch first dispatches on the lengths, to save on comparisons.
    if (cats.length > 3) {
        cats.sort(function(a, b) {return b.length - a.length;});
        f += "switch(str.length){";
        for (var i = 0; i < cats.length; ++i) {
            var cat = cats[i];
            f += "case " + cat[0].length + ":";
            compareTo(cat);
        }
        f += "}";
        // Otherwise, simply generate a flat `switch` statement.
    } else {
        compareTo(words);
    }
    return new Function("str", f);
};

function all(array, predicate) {
    for (var i = array.length; --i >= 0;)
        if (!predicate(array[i]))
            return false;
    return true;
};

function Dictionary() {
    this._values = Object.create(null);
    this._size = 0;
};
Dictionary.prototype = {
    set: function(key, val) {
        if (!this.has(key)) ++this._size;
        this._values["$" + key] = val;
        return this;
    },
    add: function(key, val) {
        if (this.has(key)) {
            this.get(key).push(val);
        } else {
            this.set(key, [ val ]);
        }
        return this;
    },
    get: function(key) { return this._values["$" + key] },
    del: function(key) {
        if (this.has(key)) {
            --this._size;
            delete this._values["$" + key];
        }
        return this;
    },
    has: function(key) { return ("$" + key) in this._values },
    each: function(f) {
        for (var i in this._values)
            f(this._values[i], i.substr(1));
    },
    size: function() {
        return this._size;
    },
    map: function(f) {
        var ret = [];
        for (var i in this._values)
            ret.push(f(this._values[i], i.substr(1)));
        return ret;
    },
    clone: function() {
        var ret = new Dictionary();
        for (var i in this._values)
            ret._values[i] = this._values[i];
        ret._size = this._size;
        return ret;
    },
    toObject: function() { return this._values }
};
Dictionary.fromObject = function(obj) {
    var dict = new Dictionary();
    dict._size = merge(dict._values, obj);
    return dict;
};

function HOP(obj, prop) {
    return Object.prototype.hasOwnProperty.call(obj, prop);
}

// return true if the node at the top of the stack (that means the
// innermost node in the current output) is lexically the first in
// a statement.
function first_in_statement(stack) {
    var node = stack.parent(-1);
    for (var i = 0, p; p = stack.parent(i); i++) {
        if (p instanceof AST_Statement && p.body === node)
            return true;
        if ((p instanceof AST_Sequence      && p.expressions[0] === node) ||
            (p.TYPE == "Call"               && p.expression === node ) ||
            (p instanceof AST_Dot           && p.expression === node ) ||
            (p instanceof AST_Sub           && p.expression === node ) ||
            (p instanceof AST_Conditional   && p.condition === node  ) ||
            (p instanceof AST_Binary        && p.left === node       ) ||
            (p instanceof AST_UnaryPostfix  && p.expression === node ))
        {
            node = p;
        } else {
            return false;
        }
    }
}

/***********************************************************************

  A JavaScript tokenizer / parser / beautifier / compressor.
  https://github.com/mishoo/UglifyJS2

  -------------------------------- (C) ---------------------------------

                           Author: Mihai Bazon
                         <mihai.bazon@gmail.com>
                       http://mihai.bazon.net/blog

  Distributed under the BSD license:

    Copyright 2012 (c) Mihai Bazon <mihai.bazon@gmail.com>

    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions
    are met:

        * Redistributions of source code must retain the above
          copyright notice, this list of conditions and the following
          disclaimer.

        * Redistributions in binary form must reproduce the above
          copyright notice, this list of conditions and the following
          disclaimer in the documentation and/or other materials
          provided with the distribution.

    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER “AS IS” AND ANY
    EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
    IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
    PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER BE
    LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY,
    OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
    PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
    PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
    THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR
    TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
    THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
    SUCH DAMAGE.

 ***********************************************************************/

"use strict";

function DEFNODE(type, props, methods, base) {
    if (arguments.length < 4) base = AST_Node;
    if (!props) props = [];
    else props = props.split(/\s+/);
    var self_props = props;
    if (base && base.PROPS)
        props = props.concat(base.PROPS);
    var code = "return function AST_" + type + "(props){ if (props) { ";
    for (var i = props.length; --i >= 0;) {
        code += "this." + props[i] + " = props." + props[i] + ";";
    }
    var proto = base && new base;
    if (proto && proto.initialize || (methods && methods.initialize))
        code += "this.initialize();";
    code += "}}";
    var ctor = new Function(code)();
    if (proto) {
        ctor.prototype = proto;
        ctor.BASE = base;
    }
    if (base) base.SUBCLASSES.push(ctor);
    ctor.prototype.CTOR = ctor;
    ctor.PROPS = props || null;
    ctor.SELF_PROPS = self_props;
    ctor.SUBCLASSES = [];
    if (type) {
        ctor.prototype.TYPE = ctor.TYPE = type;
    }
    if (methods) for (i in methods) if (HOP(methods, i)) {
        if (/^\$/.test(i)) {
            ctor[i.substr(1)] = methods[i];
        } else {
            ctor.prototype[i] = methods[i];
        }
    }
    ctor.DEFMETHOD = function(name, method) {
        this.prototype[name] = method;
    };
    if (typeof exports !== "undefined") {
        exports["AST_" + type] = ctor;
    }
    return ctor;
};

var AST_Token = DEFNODE("Token", "type value line col pos endline endcol endpos nlb comments_before comments_after file raw", {
}, null);

var AST_Node = DEFNODE("Node", "start end", {
    _clone: function(deep) {
        if (deep) {
            var self = this.clone();
            return self.transform(new TreeTransformer(function(node) {
                if (node !== self) {
                    return node.clone(true);
                }
            }));
        }
        return new this.CTOR(this);
    },
    clone: function(deep) {
        return this._clone(deep);
    },
    $documentation: "Base class of all AST nodes",
    $propdoc: {
        start: "[AST_Token] The first token of this node",
        end: "[AST_Token] The last token of this node"
    },
    _walk: function(visitor) {
        return visitor._visit(this);
    },
    walk: function(visitor) {
        return this._walk(visitor); // not sure the indirection will be any help
    }
}, null);

AST_Node.warn_function = null;
AST_Node.warn = function(txt, props) {
    if (AST_Node.warn_function)
        AST_Node.warn_function(string_template(txt, props));
};

/* -----[ statements ]----- */

var AST_Statement = DEFNODE("Statement", null, {
    $documentation: "Base class of all statements",
});

var AST_Debugger = DEFNODE("Debugger", null, {
    $documentation: "Represents a debugger statement",
}, AST_Statement);

var AST_Directive = DEFNODE("Directive", "value quote", {
    $documentation: "Represents a directive, like \"use strict\";",
    $propdoc: {
        value: "[string] The value of this directive as a plain string (it's not an AST_String!)",
        quote: "[string] the original quote character"
    },
}, AST_Statement);

var AST_SimpleStatement = DEFNODE("SimpleStatement", "body", {
    $documentation: "A statement consisting of an expression, i.e. a = 1 + 2",
    $propdoc: {
        body: "[AST_Node] an expression node (should not be instanceof AST_Statement)"
    },
    _walk: function(visitor) {
        return visitor._visit(this, function(){
            this.body._walk(visitor);
        });
    }
}, AST_Statement);

function walk_body(node, visitor) {
    var body = node.body;
    if (body instanceof AST_Node) {
        body._walk(visitor);
    }
    else for (var i = 0, len = body.length; i < len; i++) {
        body[i]._walk(visitor);
    }
};

var AST_Block = DEFNODE("Block", "body", {
    $documentation: "A body of statements (usually bracketed)",
    $propdoc: {
        body: "[AST_Statement*] an array of statements"
    },
    _walk: function(visitor) {
        return visitor._visit(this, function(){
            walk_body(this, visitor);
        });
    }
}, AST_Statement);

var AST_BlockStatement = DEFNODE("BlockStatement", null, {
    $documentation: "A block statement",
}, AST_Block);

var AST_EmptyStatement = DEFNODE("EmptyStatement", null, {
    $documentation: "The empty statement (empty block or simply a semicolon)"
}, AST_Statement);

var AST_StatementWithBody = DEFNODE("StatementWithBody", "body", {
    $documentation: "Base class for all statements that contain one nested body: `For`, `ForIn`, `Do`, `While`, `With`",
    $propdoc: {
        body: "[AST_Statement] the body; this should always be present, even if it's an AST_EmptyStatement"
    }
}, AST_Statement);

var AST_LabeledStatement = DEFNODE("LabeledStatement", "label", {
    $documentation: "Statement with a label",
    $propdoc: {
        label: "[AST_Label] a label definition"
    },
    _walk: function(visitor) {
        return visitor._visit(this, function(){
            this.label._walk(visitor);
            this.body._walk(visitor);
        });
    },
    clone: function(deep) {
        var node = this._clone(deep);
        if (deep) {
            var label = node.label;
            var def = this.label;
            node.walk(new TreeWalker(function(node) {
                if (node instanceof AST_LoopControl
                    && node.label && node.label.thedef === def) {
                    node.label.thedef = label;
                    label.references.push(node);
                }
            }));
        }
        return node;
    }
}, AST_StatementWithBody);

var AST_IterationStatement = DEFNODE("IterationStatement", null, {
    $documentation: "Internal class.  All loops inherit from it."
}, AST_StatementWithBody);

var AST_DWLoop = DEFNODE("DWLoop", "condition", {
    $documentation: "Base class for do/while statements",
    $propdoc: {
        condition: "[AST_Node] the loop condition.  Should not be instanceof AST_Statement"
    }
}, AST_IterationStatement);

var AST_Do = DEFNODE("Do", null, {
    $documentation: "A `do` statement",
    _walk: function(visitor) {
        return visitor._visit(this, function(){
            this.body._walk(visitor);
            this.condition._walk(visitor);
        });
    }
}, AST_DWLoop);

var AST_While = DEFNODE("While", null, {
    $documentation: "A `while` statement",
    _walk: function(visitor) {
        return visitor._visit(this, function(){
            this.condition._walk(visitor);
            this.body._walk(visitor);
        });
    }
}, AST_DWLoop);

var AST_For = DEFNODE("For", "init condition step", {
    $documentation: "A `for` statement",
    $propdoc: {
        init: "[AST_Node?] the `for` initialization code, or null if empty",
        condition: "[AST_Node?] the `for` termination clause, or null if empty",
        step: "[AST_Node?] the `for` update clause, or null if empty"
    },
    _walk: function(visitor) {
        return visitor._visit(this, function(){
            if (this.init) this.init._walk(visitor);
            if (this.condition) this.condition._walk(visitor);
            if (this.step) this.step._walk(visitor);
            this.body._walk(visitor);
        });
    }
}, AST_IterationStatement);

var AST_ForIn = DEFNODE("ForIn", "init object", {
    $documentation: "A `for ... in` statement",
    $propdoc: {
        init: "[AST_Node] the `for/in` initialization code",
        object: "[AST_Node] the object that we're looping through"
    },
    _walk: function(visitor) {
        return visitor._visit(this, function(){
            this.init._walk(visitor);
            this.object._walk(visitor);
            this.body._walk(visitor);
        });
    }
}, AST_IterationStatement);

var AST_ForOf = DEFNODE("ForOf", null, {
    $documentation: "A `for ... of` statement",
}, AST_ForIn);

var AST_With = DEFNODE("With", "expression", {
    $documentation: "A `with` statement",
    $propdoc: {
        expression: "[AST_Node] the `with` expression"
    },
    _walk: function(visitor) {
        return visitor._visit(this, function(){
            this.expression._walk(visitor);
            this.body._walk(visitor);
        });
    }
}, AST_StatementWithBody);

/* -----[ scope and functions ]----- */

var AST_Scope = DEFNODE("Scope", "variables functions uses_with uses_eval parent_scope enclosed cname", {
    $documentation: "Base class for all statements introducing a lexical scope",
    $propdoc: {
        variables: "[Object/S] a map of name -> SymbolDef for all variables/functions defined in this scope",
        functions: "[Object/S] like `variables`, but only lists function declarations",
        uses_with: "[boolean/S] tells whether this scope uses the `with` statement",
        uses_eval: "[boolean/S] tells whether this scope contains a direct call to the global `eval`",
        parent_scope: "[AST_Scope?/S] link to the parent scope",
        enclosed: "[SymbolDef*/S] a list of all symbol definitions that are accessed from this scope or any subscopes",
        cname: "[integer/S] current index for mangling variables (used internally by the mangler)",
    },
    get_defun_scope: function() {
        var self = this;
        while (self.is_block_scope()) {
            self = self.parent_scope;
        }
        return self;
    },
    clone: function(deep) {
        var node = this._clone(deep);
        if (this.variables) node.variables = this.variables.clone();
        if (this.functions) node.functions = this.functions.clone();
        if (this.enclosed) node.enclosed = this.enclosed.slice();
        return node;
    }
}, AST_Block);

var AST_Toplevel = DEFNODE("Toplevel", "globals", {
    $documentation: "The toplevel scope",
    $propdoc: {
        globals: "[Object/S] a map of name -> SymbolDef for all undeclared names",
    },
    wrap_commonjs: function(name) {
        var body = this.body;
        var wrapped_tl = "(function(exports){'$ORIG';})(typeof " + name + "=='undefined'?(" + name + "={}):" + name + ");";
        wrapped_tl = parse(wrapped_tl);
        wrapped_tl = wrapped_tl.transform(new TreeTransformer(function before(node){
            if (node instanceof AST_Directive && node.value == "$ORIG") {
                return MAP.splice(body);
            }
        }));
        return wrapped_tl;
    }
}, AST_Scope);

var AST_Expansion = DEFNODE("Expansion", "expression", {
    $documentation: "An expandible argument, such as ...rest, a splat, such as [1,2,...all], or an expansion in a variable declaration, such as var [first, ...rest] = list",
    $propdoc: {
        expression: "[AST_Node] the thing to be expanded"
    },
    _walk: function(visitor) {
        var self = this;
        return visitor._visit(this, function(){
            self.expression.walk(visitor);
        });
    }
});

var AST_Lambda = DEFNODE("Lambda", "name argnames uses_arguments is_generator async", {
    $documentation: "Base class for functions",
    $propdoc: {
        name: "[AST_SymbolDeclaration?] the name of this function",
        argnames: "[AST_SymbolFunarg|AST_Destructuring|AST_Expansion|AST_DefaultAssign*] array of function arguments, destructurings, or expanding arguments",
        uses_arguments: "[boolean/S] tells whether this function accesses the arguments array",
        is_generator: "[boolean] is this a generator method",
        async: "[boolean] is this method async",
    },
    args_as_names: function () {
        var out = [];
        for (var i = 0; i < this.argnames.length; i++) {
            if (this.argnames[i] instanceof AST_Destructuring) {
                out = out.concat(this.argnames[i].all_symbols());
            } else {
                out.push(this.argnames[i]);
            }
        }
        return out;
    },
    _walk: function(visitor) {
        return visitor._visit(this, function(){
            if (this.name) this.name._walk(visitor);
            var argnames = this.argnames;
            for (var i = 0, len = argnames.length; i < len; i++) {
                argnames[i]._walk(visitor);
            }
            walk_body(this, visitor);
        });
    }
}, AST_Scope);

var AST_Accessor = DEFNODE("Accessor", null, {
    $documentation: "A setter/getter function.  The `name` property is always null."
}, AST_Lambda);

var AST_Function = DEFNODE("Function", "inlined", {
    $documentation: "A function expression"
}, AST_Lambda);

var AST_Arrow = DEFNODE("Arrow", "inlined", {
    $documentation: "An ES6 Arrow function ((a) => b)"
}, AST_Lambda);

var AST_Defun = DEFNODE("Defun", "inlined", {
    $documentation: "A function definition"
}, AST_Lambda);

/* -----[ DESTRUCTURING ]----- */
var AST_Destructuring = DEFNODE("Destructuring", "names is_array", {
    $documentation: "A destructuring of several names. Used in destructuring assignment and with destructuring function argument names",
    $propdoc: {
        "names": "[AST_Node*] Array of properties or elements",
        "is_array": "[Boolean] Whether the destructuring represents an object or array"
    },
    _walk: function(visitor) {
        return visitor._visit(this, function(){
            this.names.forEach(function(name){
                name._walk(visitor);
            });
        });
    },
    all_symbols: function() {
        var out = [];
        this.walk(new TreeWalker(function (node) {
            if (node instanceof AST_Symbol) {
                out.push(node);
            }
            if (node instanceof AST_Expansion) {
                out.push(node.expression);
            }
        }));
        return out;
    }
});

var AST_PrefixedTemplateString = DEFNODE("PrefixedTemplateString", "template_string prefix", {
    $documentation: "A templatestring with a prefix, such as String.raw`foobarbaz`",
    $propdoc: {
        template_string: "[AST_TemplateString] The template string",
        prefix: "[AST_SymbolRef|AST_PropAccess] The prefix, which can be a symbol such as `foo` or a dotted expression such as `String.raw`."
    },
    _walk: function(visitor) {
        this.prefix._walk(visitor);
        this.template_string._walk(visitor);
    }
})

var AST_TemplateString = DEFNODE("TemplateString", "segments", {
    $documentation: "A template string literal",
    $propdoc: {
        segments: "[AST_Node*] One or more segments, starting with AST_TemplateSegment. AST_Node may follow AST_TemplateSegment, but each AST_Node must be followed by AST_TemplateSegment."
    },
    _walk: function(visitor) {
        return visitor._visit(this, function(){
            this.segments.forEach(function(seg){
                seg._walk(visitor);
            });
        });
    }
});

var AST_TemplateSegment = DEFNODE("TemplateSegment", "value raw", {
    $documentation: "A segment of a template string literal",
    $propdoc: {
        value: "Content of the segment",
        raw: "Raw content of the segment"
    }
});

/* -----[ JUMPS ]----- */

var AST_Jump = DEFNODE("Jump", null, {
    $documentation: "Base class for “jumps” (for now that's `return`, `throw`, `break` and `continue`)"
}, AST_Statement);

var AST_Exit = DEFNODE("Exit", "value", {
    $documentation: "Base class for “exits” (`return` and `throw`)",
    $propdoc: {
        value: "[AST_Node?] the value returned or thrown by this statement; could be null for AST_Return"
    },
    _walk: function(visitor) {
        return visitor._visit(this, this.value && function(){
            this.value._walk(visitor);
        });
    }
}, AST_Jump);

var AST_Return = DEFNODE("Return", null, {
    $documentation: "A `return` statement"
}, AST_Exit);

var AST_Throw = DEFNODE("Throw", null, {
    $documentation: "A `throw` statement"
}, AST_Exit);

var AST_LoopControl = DEFNODE("LoopControl", "label", {
    $documentation: "Base class for loop control statements (`break` and `continue`)",
    $propdoc: {
        label: "[AST_LabelRef?] the label, or null if none",
    },
    _walk: function(visitor) {
        return visitor._visit(this, this.label && function(){
            this.label._walk(visitor);
        });
    }
}, AST_Jump);

var AST_Break = DEFNODE("Break", null, {
    $documentation: "A `break` statement"
}, AST_LoopControl);

var AST_Continue = DEFNODE("Continue", null, {
    $documentation: "A `continue` statement"
}, AST_LoopControl);

/* -----[ IF ]----- */

var AST_If = DEFNODE("If", "condition alternative", {
    $documentation: "A `if` statement",
    $propdoc: {
        condition: "[AST_Node] the `if` condition",
        alternative: "[AST_Statement?] the `else` part, or null if not present"
    },
    _walk: function(visitor) {
        return visitor._visit(this, function(){
            this.condition._walk(visitor);
            this.body._walk(visitor);
            if (this.alternative) this.alternative._walk(visitor);
        });
    }
}, AST_StatementWithBody);

/* -----[ SWITCH ]----- */

var AST_Switch = DEFNODE("Switch", "expression", {
    $documentation: "A `switch` statement",
    $propdoc: {
        expression: "[AST_Node] the `switch` “discriminant”"
    },
    _walk: function(visitor) {
        return visitor._visit(this, function(){
            this.expression._walk(visitor);
            walk_body(this, visitor);
        });
    }
}, AST_Block);

var AST_SwitchBranch = DEFNODE("SwitchBranch", null, {
    $documentation: "Base class for `switch` branches",
}, AST_Block);

var AST_Default = DEFNODE("Default", null, {
    $documentation: "A `default` switch branch",
}, AST_SwitchBranch);

var AST_Case = DEFNODE("Case", "expression", {
    $documentation: "A `case` switch branch",
    $propdoc: {
        expression: "[AST_Node] the `case` expression"
    },
    _walk: function(visitor) {
        return visitor._visit(this, function(){
            this.expression._walk(visitor);
            walk_body(this, visitor);
        });
    }
}, AST_SwitchBranch);

/* -----[ EXCEPTIONS ]----- */

var AST_Try = DEFNODE("Try", "bcatch bfinally", {
    $documentation: "A `try` statement",
    $propdoc: {
        bcatch: "[AST_Catch?] the catch block, or null if not present",
        bfinally: "[AST_Finally?] the finally block, or null if not present"
    },
    _walk: function(visitor) {
        return visitor._visit(this, function(){
            walk_body(this, visitor);
            if (this.bcatch) this.bcatch._walk(visitor);
            if (this.bfinally) this.bfinally._walk(visitor);
        });
    }
}, AST_Block);

var AST_Catch = DEFNODE("Catch", "argname", {
    $documentation: "A `catch` node; only makes sense as part of a `try` statement",
    $propdoc: {
        argname: "[AST_SymbolCatch|AST_Destructuring|AST_Expansion|AST_DefaultAssign] symbol for the exception"
    },
    _walk: function(visitor) {
        return visitor._visit(this, function(){
            this.argname._walk(visitor);
            walk_body(this, visitor);
        });
    }
}, AST_Block);

var AST_Finally = DEFNODE("Finally", null, {
    $documentation: "A `finally` node; only makes sense as part of a `try` statement"
}, AST_Block);

/* -----[ VAR/CONST ]----- */

var AST_Definitions = DEFNODE("Definitions", "definitions", {
    $documentation: "Base class for `var` or `const` nodes (variable declarations/initializations)",
    $propdoc: {
        definitions: "[AST_VarDef*] array of variable definitions"
    },
    _walk: function(visitor) {
        return visitor._visit(this, function(){
            var definitions = this.definitions;
            for (var i = 0, len = definitions.length; i < len; i++) {
                definitions[i]._walk(visitor);
            }
        });
    }
}, AST_Statement);

var AST_Var = DEFNODE("Var", null, {
    $documentation: "A `var` statement"
}, AST_Definitions);

var AST_Let = DEFNODE("Let", null, {
    $documentation: "A `let` statement"
}, AST_Definitions);

var AST_Const = DEFNODE("Const", null, {
    $documentation: "A `const` statement"
}, AST_Definitions);

var AST_NameMapping = DEFNODE("NameMapping", "foreign_name name", {
    $documentation: "The part of the export/import statement that declare names from a module.",
    $propdoc: {
        foreign_name: "[AST_SymbolExportForeign|AST_SymbolImportForeign] The name being exported/imported (as specified in the module)",
        name: "[AST_SymbolExport|AST_SymbolImport] The name as it is visible to this module."
    },
    _walk: function (visitor) {
        return visitor._visit(this, function() {
            this.foreign_name._walk(visitor);
            this.name._walk(visitor);
        });
    }
})

var AST_Import = DEFNODE("Import", "imported_name imported_names module_name", {
    $documentation: "An `import` statement",
    $propdoc: {
        imported_name: "[AST_SymbolImport] The name of the variable holding the module's default export.",
        imported_names: "[AST_NameMapping*] The names of non-default imported variables",
        module_name: "[AST_String] String literal describing where this module came from",
    },
    _walk: function(visitor) {
        return visitor._visit(this, function() {
            if (this.imported_name) {
                this.imported_name._walk(visitor);
            }
            if (this.imported_names) {
                this.imported_names.forEach(function(name_import) {
                    name_import._walk(visitor);
                });
            }
            this.module_name._walk(visitor);
        });
    }
});

var AST_Export = DEFNODE("Export", "exported_definition exported_value is_default exported_names module_name", {
    $documentation: "An `export` statement",
    $propdoc: {
        exported_definition: "[AST_Defun|AST_Definitions|AST_DefClass?] An exported definition",
        exported_value: "[AST_Node?] An exported value",
        exported_names: "[AST_NameMapping*?] List of exported names",
        module_name: "[AST_String?] Name of the file to load exports from",
        is_default: "[Boolean] Whether this is the default exported value of this module"
    },
    _walk: function (visitor) {
        visitor._visit(this, function () {
            if (this.exported_definition) {
                this.exported_definition._walk(visitor);
            }
            if (this.exported_value) {
                this.exported_value._walk(visitor);
            }
            if (this.exported_names) {
                this.exported_names.forEach(function(name_export) {
                    name_export._walk(visitor);
                });
            }
            if (this.module_name) {
                this.module_name._walk(visitor);
            }
        });
    }
}, AST_Statement);

var AST_VarDef = DEFNODE("VarDef", "name value", {
    $documentation: "A variable declaration; only appears in a AST_Definitions node",
    $propdoc: {
        name: "[AST_Destructuring|AST_SymbolConst|AST_SymbolLet|AST_SymbolVar] name of the variable",
        value: "[AST_Node?] initializer, or null of there's no initializer"
    },
    _walk: function(visitor) {
        return visitor._visit(this, function(){
            this.name._walk(visitor);
            if (this.value) this.value._walk(visitor);
        });
    }
});

/* -----[ OTHER ]----- */

var AST_Call = DEFNODE("Call", "expression args", {
    $documentation: "A function call expression",
    $propdoc: {
        expression: "[AST_Node] expression to invoke as function",
        args: "[AST_Node*] array of arguments"
    },
    _walk: function(visitor) {
        return visitor._visit(this, function(){
            var args = this.args;
            for (var i = 0, len = args.length; i < len; i++) {
                args[i]._walk(visitor);
            }
            this.expression._walk(visitor);
        });
    }
});

var AST_New = DEFNODE("New", null, {
    $documentation: "An object instantiation.  Derives from a function call since it has exactly the same properties"
}, AST_Call);

var AST_Sequence = DEFNODE("Sequence", "expressions", {
    $documentation: "A sequence expression (comma-separated expressions)",
    $propdoc: {
        expressions: "[AST_Node*] array of expressions (at least two)"
    },
    _walk: function(visitor) {
        return visitor._visit(this, function(){
            this.expressions.forEach(function(node) {
                node._walk(visitor);
            });
        });
    }
});

var AST_PropAccess = DEFNODE("PropAccess", "expression property", {
    $documentation: "Base class for property access expressions, i.e. `a.foo` or `a[\"foo\"]`",
    $propdoc: {
        expression: "[AST_Node] the “container” expression",
        property: "[AST_Node|string] the property to access.  For AST_Dot this is always a plain string, while for AST_Sub it's an arbitrary AST_Node"
    }
});

var AST_Dot = DEFNODE("Dot", null, {
    $documentation: "A dotted property access expression",
    _walk: function(visitor) {
        return visitor._visit(this, function(){
            this.expression._walk(visitor);
        });
    }
}, AST_PropAccess);

var AST_Sub = DEFNODE("Sub", null, {
    $documentation: "Index-style property access, i.e. `a[\"foo\"]`",
    _walk: function(visitor) {
        return visitor._visit(this, function(){
            this.expression._walk(visitor);
            this.property._walk(visitor);
        });
    }
}, AST_PropAccess);

var AST_Unary = DEFNODE("Unary", "operator expression", {
    $documentation: "Base class for unary expressions",
    $propdoc: {
        operator: "[string] the operator",
        expression: "[AST_Node] expression that this unary operator applies to"
    },
    _walk: function(visitor) {
        return visitor._visit(this, function(){
            this.expression._walk(visitor);
        });
    }
});

var AST_UnaryPrefix = DEFNODE("UnaryPrefix", null, {
    $documentation: "Unary prefix expression, i.e. `typeof i` or `++i`"
}, AST_Unary);

var AST_UnaryPostfix = DEFNODE("UnaryPostfix", null, {
    $documentation: "Unary postfix expression, i.e. `i++`"
}, AST_Unary);

var AST_Binary = DEFNODE("Binary", "operator left right", {
    $documentation: "Binary expression, i.e. `a + b`",
    $propdoc: {
        left: "[AST_Node] left-hand side expression",
        operator: "[string] the operator",
        right: "[AST_Node] right-hand side expression"
    },
    _walk: function(visitor) {
        return visitor._visit(this, function(){
            this.left._walk(visitor);
            this.right._walk(visitor);
        });
    }
});

var AST_Conditional = DEFNODE("Conditional", "condition consequent alternative", {
    $documentation: "Conditional expression using the ternary operator, i.e. `a ? b : c`",
    $propdoc: {
        condition: "[AST_Node]",
        consequent: "[AST_Node]",
        alternative: "[AST_Node]"
    },
    _walk: function(visitor) {
        return visitor._visit(this, function(){
            this.condition._walk(visitor);
            this.consequent._walk(visitor);
            this.alternative._walk(visitor);
        });
    }
});

var AST_Assign = DEFNODE("Assign", null, {
    $documentation: "An assignment expression — `a = b + 5`",
}, AST_Binary);

var AST_DefaultAssign = DEFNODE("DefaultAssign", null, {
    $documentation: "A default assignment expression like in `(a = 3) => a`"
}, AST_Binary);

/* -----[ LITERALS ]----- */

var AST_Array = DEFNODE("Array", "elements", {
    $documentation: "An array literal",
    $propdoc: {
        elements: "[AST_Node*] array of elements"
    },
    _walk: function(visitor) {
        return visitor._visit(this, function(){
            var elements = this.elements;
            for (var i = 0, len = elements.length; i < len; i++) {
                elements[i]._walk(visitor);
            }
        });
    }
});

var AST_Object = DEFNODE("Object", "properties", {
    $documentation: "An object literal",
    $propdoc: {
        properties: "[AST_ObjectProperty*] array of properties"
    },
    _walk: function(visitor) {
        return visitor._visit(this, function(){
            var properties = this.properties;
            for (var i = 0, len = properties.length; i < len; i++) {
                properties[i]._walk(visitor);
            }
        });
    }
});

var AST_ObjectProperty = DEFNODE("ObjectProperty", "key value", {
    $documentation: "Base class for literal object properties",
    $propdoc: {
        key: "[string|AST_Node] property name. For ObjectKeyVal this is a string. For getters, setters and computed property this is an AST_Node.",
        value: "[AST_Node] property value.  For getters and setters this is an AST_Accessor."
    },
    _walk: function(visitor) {
        return visitor._visit(this, function(){
            if (this.key instanceof AST_Node)
                this.key._walk(visitor);
            this.value._walk(visitor);
        });
    }
});

var AST_ObjectKeyVal = DEFNODE("ObjectKeyVal", "quote", {
    $documentation: "A key: value object property",
    $propdoc: {
        quote: "[string] the original quote character"
    }
}, AST_ObjectProperty);

var AST_ObjectSetter = DEFNODE("ObjectSetter", "quote static", {
    $propdoc: {
        quote: "[string|undefined] the original quote character, if any",
        static: "[boolean] whether this is a static setter (classes only)"
    },
    $documentation: "An object setter property",
}, AST_ObjectProperty);

var AST_ObjectGetter = DEFNODE("ObjectGetter", "quote static", {
    $propdoc: {
        quote: "[string|undefined] the original quote character, if any",
        static: "[boolean] whether this is a static getter (classes only)"
    },
    $documentation: "An object getter property",
}, AST_ObjectProperty);

var AST_ConciseMethod = DEFNODE("ConciseMethod", "quote static is_generator async", {
    $propdoc: {
        quote: "[string|undefined] the original quote character, if any",
        static: "[boolean] is this method static (classes only)",
        is_generator: "[boolean] is this a generator method",
        async: "[boolean] is this method async",
    },
    $documentation: "An ES6 concise method inside an object or class"
}, AST_ObjectProperty);

var AST_Class = DEFNODE("Class", "name extends properties inlined", {
    $propdoc: {
        name: "[AST_SymbolClass|AST_SymbolDefClass?] optional class name.",
        extends: "[AST_Node]? optional parent class",
        properties: "[AST_ObjectProperty*] array of properties"
    },
    $documentation: "An ES6 class",
    _walk: function(visitor) {
        return visitor._visit(this, function(){
            if (this.name) {
                this.name._walk(visitor);
            }
            if (this.extends) {
                this.extends._walk(visitor);
            }
            this.properties.forEach(function(prop){
                prop._walk(visitor);
            });
        });
    },
}, AST_Scope);

var AST_DefClass = DEFNODE("DefClass", null, {
    $documentation: "A class definition",
}, AST_Class);

var AST_ClassExpression = DEFNODE("ClassExpression", null, {
    $documentation: "A class expression."
}, AST_Class);

var AST_Symbol = DEFNODE("Symbol", "scope name thedef", {
    $propdoc: {
        name: "[string] name of this symbol",
        scope: "[AST_Scope/S] the current scope (not necessarily the definition scope)",
        thedef: "[SymbolDef/S] the definition of this symbol"
    },
    $documentation: "Base class for all symbols"
});

var AST_NewTarget = DEFNODE("NewTarget", null, {
    $documentation: "A reference to new.target"
});

var AST_SymbolDeclaration = DEFNODE("SymbolDeclaration", "init", {
    $documentation: "A declaration symbol (symbol in var/const, function name or argument, symbol in catch)",
}, AST_Symbol);

var AST_SymbolVar = DEFNODE("SymbolVar", null, {
    $documentation: "Symbol defining a variable",
}, AST_SymbolDeclaration);

var AST_SymbolBlockDeclaration = DEFNODE("SymbolBlockDeclaration", null, {
    $documentation: "Base class for block-scoped declaration symbols"
}, AST_SymbolDeclaration);

var AST_SymbolConst = DEFNODE("SymbolConst", null, {
    $documentation: "A constant declaration"
}, AST_SymbolBlockDeclaration);

var AST_SymbolLet = DEFNODE("SymbolLet", null, {
    $documentation: "A block-scoped `let` declaration"
}, AST_SymbolBlockDeclaration);

var AST_SymbolFunarg = DEFNODE("SymbolFunarg", null, {
    $documentation: "Symbol naming a function argument",
}, AST_SymbolVar);

var AST_SymbolDefun = DEFNODE("SymbolDefun", null, {
    $documentation: "Symbol defining a function",
}, AST_SymbolDeclaration);

var AST_SymbolMethod = DEFNODE("SymbolMethod", null, {
    $documentation: "Symbol in an object defining a method",
}, AST_Symbol);

var AST_SymbolLambda = DEFNODE("SymbolLambda", null, {
    $documentation: "Symbol naming a function expression",
}, AST_SymbolDeclaration);

var AST_SymbolDefClass = DEFNODE("SymbolDefClass", null, {
    $documentation: "Symbol naming a class's name in a class declaration. Lexically scoped to its containing scope, and accessible within the class."
}, AST_SymbolBlockDeclaration);

var AST_SymbolClass = DEFNODE("SymbolClass", null, {
    $documentation: "Symbol naming a class's name. Lexically scoped to the class."
}, AST_SymbolDeclaration);

var AST_SymbolCatch = DEFNODE("SymbolCatch", null, {
    $documentation: "Symbol naming the exception in catch",
}, AST_SymbolBlockDeclaration);

var AST_SymbolImport = DEFNODE("SymbolImport", null, {
    $documentation: "Symbol referring to an imported name",
}, AST_SymbolBlockDeclaration);

var AST_SymbolImportForeign = DEFNODE("SymbolImportForeign", null, {
    $documentation: "A symbol imported from a module, but it is defined in the other module, and its real name is irrelevant for this module's purposes",
}, AST_Symbol);

var AST_Label = DEFNODE("Label", "references", {
    $documentation: "Symbol naming a label (declaration)",
    $propdoc: {
        references: "[AST_LoopControl*] a list of nodes referring to this label"
    },
    initialize: function() {
        this.references = [];
        this.thedef = this;
    }
}, AST_Symbol);

var AST_SymbolRef = DEFNODE("SymbolRef", null, {
    $documentation: "Reference to some symbol (not definition/declaration)",
}, AST_Symbol);

var AST_SymbolExport = DEFNODE("SymbolExport", null, {
    $documentation: "Symbol referring to a name to export",
}, AST_SymbolRef);

var AST_SymbolExportForeign = DEFNODE("SymbolExportForeign", null, {
    $documentation: "A symbol exported from this module, but it is used in the other module, and its real name is irrelevant for this module's purposes",
}, AST_Symbol);

var AST_LabelRef = DEFNODE("LabelRef", null, {
    $documentation: "Reference to a label symbol",
}, AST_Symbol);

var AST_This = DEFNODE("This", null, {
    $documentation: "The `this` symbol",
}, AST_Symbol);

var AST_Super = DEFNODE("Super", null, {
    $documentation: "The `super` symbol",
}, AST_This);

var AST_Constant = DEFNODE("Constant", null, {
    $documentation: "Base class for all constants",
    getValue: function() {
        return this.value;
    }
});

var AST_String = DEFNODE("String", "value quote", {
    $documentation: "A string literal",
    $propdoc: {
        value: "[string] the contents of this string",
        quote: "[string] the original quote character"
    }
}, AST_Constant);

var AST_Number = DEFNODE("Number", "value literal", {
    $documentation: "A number literal",
    $propdoc: {
        value: "[number] the numeric value",
        literal: "[string] numeric value as string (optional)"
    }
}, AST_Constant);

var AST_RegExp = DEFNODE("RegExp", "value", {
    $documentation: "A regexp literal",
    $propdoc: {
        value: "[RegExp] the actual regexp"
    }
}, AST_Constant);

var AST_Atom = DEFNODE("Atom", null, {
    $documentation: "Base class for atoms",
}, AST_Constant);

var AST_Null = DEFNODE("Null", null, {
    $documentation: "The `null` atom",
    value: null
}, AST_Atom);

var AST_NaN = DEFNODE("NaN", null, {
    $documentation: "The impossible value",
    value: 0/0
}, AST_Atom);

var AST_Undefined = DEFNODE("Undefined", null, {
    $documentation: "The `undefined` value",
    value: (function(){}())
}, AST_Atom);

var AST_Hole = DEFNODE("Hole", null, {
    $documentation: "A hole in an array",
    value: (function(){}())
}, AST_Atom);

var AST_Infinity = DEFNODE("Infinity", null, {
    $documentation: "The `Infinity` value",
    value: 1/0
}, AST_Atom);

var AST_Boolean = DEFNODE("Boolean", null, {
    $documentation: "Base class for booleans",
}, AST_Atom);

var AST_False = DEFNODE("False", null, {
    $documentation: "The `false` atom",
    value: false
}, AST_Boolean);

var AST_True = DEFNODE("True", null, {
    $documentation: "The `true` atom",
    value: true
}, AST_Boolean);

var AST_Await = DEFNODE("Await", "expression", {
    $documentation: "An `await` statement",
    $propdoc: {
        expression: "[AST_Node] the mandatory expression being awaited",
    },
    _walk: function(visitor) {
        return visitor._visit(this, function(){
            this.expression._walk(visitor);
        });
    }
});

var AST_Yield = DEFNODE("Yield", "expression is_star", {
    $documentation: "A `yield` statement",
    $propdoc: {
        expression: "[AST_Node?] the value returned or thrown by this statement; could be null (representing undefined) but only when is_star is set to false",
        is_star: "[Boolean] Whether this is a yield or yield* statement"
    },
    _walk: function(visitor) {
        return visitor._visit(this, this.expression && function(){
            this.expression._walk(visitor);
        });
    }
});

/* -----[ TreeWalker ]----- */

function TreeWalker(callback) {
    this.visit = callback;
    this.stack = [];
    this.directives = Object.create(null);
};
TreeWalker.prototype = {
    _visit: function(node, descend) {
        this.push(node);
        var ret = this.visit(node, descend ? function(){
            descend.call(node);
        } : noop);
        if (!ret && descend) {
            descend.call(node);
        }
        this.pop();
        return ret;
    },
    parent: function(n) {
        return this.stack[this.stack.length - 2 - (n || 0)];
    },
    push: function(node) {
        if (node instanceof AST_Lambda) {
            this.directives = Object.create(this.directives);
        } else if (node instanceof AST_Directive && !this.directives[node.value]) {
            this.directives[node.value] = node;
        } else if (node instanceof AST_Class) {
            this.directives = Object.create(this.directives);
            if (!this.directives["use strict"]) {
                this.directives["use strict"] = node;
            }
        }
        this.stack.push(node);
    },
    pop: function() {
        var node = this.stack.pop();
        if (node instanceof AST_Lambda || node instanceof AST_Class) {
            this.directives = Object.getPrototypeOf(this.directives);
        }
    },
    self: function() {
        return this.stack[this.stack.length - 1];
    },
    find_parent: function(type) {
        var stack = this.stack;
        for (var i = stack.length; --i >= 0;) {
            var x = stack[i];
            if (x instanceof type) return x;
        }
    },
    has_directive: function(type) {
        var dir = this.directives[type];
        if (dir) return dir;
        var node = this.stack[this.stack.length - 1];
        if (node instanceof AST_Scope && node.body) {
            for (var i = 0; i < node.body.length; ++i) {
                var st = node.body[i];
                if (!(st instanceof AST_Directive)) break;
                if (st.value == type) return st;
            }
        }
    },
    loopcontrol_target: function(node) {
        var stack = this.stack;
        if (node.label) for (var i = stack.length; --i >= 0;) {
            var x = stack[i];
            if (x instanceof AST_LabeledStatement && x.label.name == node.label.name)
                return x.body;
        } else for (var i = stack.length; --i >= 0;) {
            var x = stack[i];
            if (x instanceof AST_IterationStatement
                || node instanceof AST_Break && x instanceof AST_Switch)
                return x;
        }
    }
};

/***********************************************************************

  A JavaScript tokenizer / parser / beautifier / compressor.
  https://github.com/mishoo/UglifyJS2

  -------------------------------- (C) ---------------------------------

                           Author: Mihai Bazon
                         <mihai.bazon@gmail.com>
                       http://mihai.bazon.net/blog

  Distributed under the BSD license:

    Copyright 2012 (c) Mihai Bazon <mihai.bazon@gmail.com>
    Parser based on parse-js (http://marijn.haverbeke.nl/parse-js/).

    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions
    are met:

        * Redistributions of source code must retain the above
          copyright notice, this list of conditions and the following
          disclaimer.

        * Redistributions in binary form must reproduce the above
          copyright notice, this list of conditions and the following
          disclaimer in the documentation and/or other materials
          provided with the distribution.

    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER “AS IS” AND ANY
    EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
    IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
    PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER BE
    LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY,
    OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
    PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
    PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
    THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR
    TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
    THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
    SUCH DAMAGE.

 ***********************************************************************/

"use strict";

var KEYWORDS = 'break case catch class const continue debugger default delete do else export extends finally for function if in instanceof let new return switch throw try typeof var void while with';
var KEYWORDS_ATOM = 'false null true';
var RESERVED_WORDS = 'enum implements import interface package private protected public static super this ' + KEYWORDS_ATOM + " " + KEYWORDS;
var KEYWORDS_BEFORE_EXPRESSION = 'return new delete throw else case yield await';

KEYWORDS = makePredicate(KEYWORDS);
RESERVED_WORDS = makePredicate(RESERVED_WORDS);
KEYWORDS_BEFORE_EXPRESSION = makePredicate(KEYWORDS_BEFORE_EXPRESSION);
KEYWORDS_ATOM = makePredicate(KEYWORDS_ATOM);

var OPERATOR_CHARS = makePredicate(characters("+-*&%=<>!?|~^"));

var RE_NUM_LITERAL = /[0-9a-f]/i;
var RE_HEX_NUMBER = /^0x[0-9a-f]+$/i;
var RE_OCT_NUMBER = /^0[0-7]+$/;
var RE_ES6_OCT_NUMBER = /^0o[0-7]+$/i;
var RE_BIN_NUMBER = /^0b[01]+$/i;
var RE_DEC_NUMBER = /^\d*\.?\d*(?:e[+-]?\d*(?:\d\.?|\.?\d)\d*)?$/i;

var OPERATORS = makePredicate([
    "in",
    "instanceof",
    "typeof",
    "new",
    "void",
    "delete",
    "++",
    "--",
    "+",
    "-",
    "!",
    "~",
    "&",
    "|",
    "^",
    "*",
    "**",
    "/",
    "%",
    ">>",
    "<<",
    ">>>",
    "<",
    ">",
    "<=",
    ">=",
    "==",
    "===",
    "!=",
    "!==",
    "?",
    "=",
    "+=",
    "-=",
    "/=",
    "*=",
    "**=",
    "%=",
    ">>=",
    "<<=",
    ">>>=",
    "|=",
    "^=",
    "&=",
    "&&",
    "||"
]);

var WHITESPACE_CHARS = makePredicate(characters(" \u00a0\n\r\t\f\u000b\u200b\u2000\u2001\u2002\u2003\u2004\u2005\u2006\u2007\u2008\u2009\u200a\u2028\u2029\u202f\u205f\u3000\uFEFF"));

var NEWLINE_CHARS = makePredicate(characters("\n\r\u2028\u2029"));

var PUNC_AFTER_EXPRESSION = makePredicate(characters(";]),:"));

var PUNC_BEFORE_EXPRESSION = makePredicate(characters("[{(,;:"));

var PUNC_CHARS = makePredicate(characters("[]{}(),;:"));

/* -----[ Tokenizer ]----- */

// surrogate safe regexps adapted from https://github.com/mathiasbynens/unicode-8.0.0/tree/89b412d8a71ecca9ed593d9e9fa073ab64acfebe/Binary_Property
var UNICODE = {
    ID_Start: /[A-Za-z\xAA\xB5\xBA\xC0-\xD6\xD8-\xF6\xF8-\u02C1\u02C6-\u02D1\u02E0-\u02E4\u02EC\u02EE\u0370-\u0374\u0376\u0377\u037A-\u037D\u037F\u0386\u0388-\u038A\u038C\u038E-\u03A1\u03A3-\u03F5\u03F7-\u0481\u048A-\u052F\u0531-\u0556\u0559\u0561-\u0587\u05D0-\u05EA\u05F0-\u05F2\u0620-\u064A\u066E\u066F\u0671-\u06D3\u06D5\u06E5\u06E6\u06EE\u06EF\u06FA-\u06FC\u06FF\u0710\u0712-\u072F\u074D-\u07A5\u07B1\u07CA-\u07EA\u07F4\u07F5\u07FA\u0800-\u0815\u081A\u0824\u0828\u0840-\u0858\u08A0-\u08B4\u0904-\u0939\u093D\u0950\u0958-\u0961\u0971-\u0980\u0985-\u098C\u098F\u0990\u0993-\u09A8\u09AA-\u09B0\u09B2\u09B6-\u09B9\u09BD\u09CE\u09DC\u09DD\u09DF-\u09E1\u09F0\u09F1\u0A05-\u0A0A\u0A0F\u0A10\u0A13-\u0A28\u0A2A-\u0A30\u0A32\u0A33\u0A35\u0A36\u0A38\u0A39\u0A59-\u0A5C\u0A5E\u0A72-\u0A74\u0A85-\u0A8D\u0A8F-\u0A91\u0A93-\u0AA8\u0AAA-\u0AB0\u0AB2\u0AB3\u0AB5-\u0AB9\u0ABD\u0AD0\u0AE0\u0AE1\u0AF9\u0B05-\u0B0C\u0B0F\u0B10\u0B13-\u0B28\u0B2A-\u0B30\u0B32\u0B33\u0B35-\u0B39\u0B3D\u0B5C\u0B5D\u0B5F-\u0B61\u0B71\u0B83\u0B85-\u0B8A\u0B8E-\u0B90\u0B92-\u0B95\u0B99\u0B9A\u0B9C\u0B9E\u0B9F\u0BA3\u0BA4\u0BA8-\u0BAA\u0BAE-\u0BB9\u0BD0\u0C05-\u0C0C\u0C0E-\u0C10\u0C12-\u0C28\u0C2A-\u0C39\u0C3D\u0C58-\u0C5A\u0C60\u0C61\u0C85-\u0C8C\u0C8E-\u0C90\u0C92-\u0CA8\u0CAA-\u0CB3\u0CB5-\u0CB9\u0CBD\u0CDE\u0CE0\u0CE1\u0CF1\u0CF2\u0D05-\u0D0C\u0D0E-\u0D10\u0D12-\u0D3A\u0D3D\u0D4E\u0D5F-\u0D61\u0D7A-\u0D7F\u0D85-\u0D96\u0D9A-\u0DB1\u0DB3-\u0DBB\u0DBD\u0DC0-\u0DC6\u0E01-\u0E30\u0E32\u0E33\u0E40-\u0E46\u0E81\u0E82\u0E84\u0E87\u0E88\u0E8A\u0E8D\u0E94-\u0E97\u0E99-\u0E9F\u0EA1-\u0EA3\u0EA5\u0EA7\u0EAA\u0EAB\u0EAD-\u0EB0\u0EB2\u0EB3\u0EBD\u0EC0-\u0EC4\u0EC6\u0EDC-\u0EDF\u0F00\u0F40-\u0F47\u0F49-\u0F6C\u0F88-\u0F8C\u1000-\u102A\u103F\u1050-\u1055\u105A-\u105D\u1061\u1065\u1066\u106E-\u1070\u1075-\u1081\u108E\u10A0-\u10C5\u10C7\u10CD\u10D0-\u10FA\u10FC-\u1248\u124A-\u124D\u1250-\u1256\u1258\u125A-\u125D\u1260-\u1288\u128A-\u128D\u1290-\u12B0\u12B2-\u12B5\u12B8-\u12BE\u12C0\u12C2-\u12C5\u12C8-\u12D6\u12D8-\u1310\u1312-\u1315\u1318-\u135A\u1380-\u138F\u13A0-\u13F5\u13F8-\u13FD\u1401-\u166C\u166F-\u167F\u1681-\u169A\u16A0-\u16EA\u16EE-\u16F8\u1700-\u170C\u170E-\u1711\u1720-\u1731\u1740-\u1751\u1760-\u176C\u176E-\u1770\u1780-\u17B3\u17D7\u17DC\u1820-\u1877\u1880-\u18A8\u18AA\u18B0-\u18F5\u1900-\u191E\u1950-\u196D\u1970-\u1974\u1980-\u19AB\u19B0-\u19C9\u1A00-\u1A16\u1A20-\u1A54\u1AA7\u1B05-\u1B33\u1B45-\u1B4B\u1B83-\u1BA0\u1BAE\u1BAF\u1BBA-\u1BE5\u1C00-\u1C23\u1C4D-\u1C4F\u1C5A-\u1C7D\u1CE9-\u1CEC\u1CEE-\u1CF1\u1CF5\u1CF6\u1D00-\u1DBF\u1E00-\u1F15\u1F18-\u1F1D\u1F20-\u1F45\u1F48-\u1F4D\u1F50-\u1F57\u1F59\u1F5B\u1F5D\u1F5F-\u1F7D\u1F80-\u1FB4\u1FB6-\u1FBC\u1FBE\u1FC2-\u1FC4\u1FC6-\u1FCC\u1FD0-\u1FD3\u1FD6-\u1FDB\u1FE0-\u1FEC\u1FF2-\u1FF4\u1FF6-\u1FFC\u2071\u207F\u2090-\u209C\u2102\u2107\u210A-\u2113\u2115\u2118-\u211D\u2124\u2126\u2128\u212A-\u2139\u213C-\u213F\u2145-\u2149\u214E\u2160-\u2188\u2C00-\u2C2E\u2C30-\u2C5E\u2C60-\u2CE4\u2CEB-\u2CEE\u2CF2\u2CF3\u2D00-\u2D25\u2D27\u2D2D\u2D30-\u2D67\u2D6F\u2D80-\u2D96\u2DA0-\u2DA6\u2DA8-\u2DAE\u2DB0-\u2DB6\u2DB8-\u2DBE\u2DC0-\u2DC6\u2DC8-\u2DCE\u2DD0-\u2DD6\u2DD8-\u2DDE\u3005-\u3007\u3021-\u3029\u3031-\u3035\u3038-\u303C\u3041-\u3096\u309B-\u309F\u30A1-\u30FA\u30FC-\u30FF\u3105-\u312D\u3131-\u318E\u31A0-\u31BA\u31F0-\u31FF\u3400-\u4DB5\u4E00-\u9FD5\uA000-\uA48C\uA4D0-\uA4FD\uA500-\uA60C\uA610-\uA61F\uA62A\uA62B\uA640-\uA66E\uA67F-\uA69D\uA6A0-\uA6EF\uA717-\uA71F\uA722-\uA788\uA78B-\uA7AD\uA7B0-\uA7B7\uA7F7-\uA801\uA803-\uA805\uA807-\uA80A\uA80C-\uA822\uA840-\uA873\uA882-\uA8B3\uA8F2-\uA8F7\uA8FB\uA8FD\uA90A-\uA925\uA930-\uA946\uA960-\uA97C\uA984-\uA9B2\uA9CF\uA9E0-\uA9E4\uA9E6-\uA9EF\uA9FA-\uA9FE\uAA00-\uAA28\uAA40-\uAA42\uAA44-\uAA4B\uAA60-\uAA76\uAA7A\uAA7E-\uAAAF\uAAB1\uAAB5\uAAB6\uAAB9-\uAABD\uAAC0\uAAC2\uAADB-\uAADD\uAAE0-\uAAEA\uAAF2-\uAAF4\uAB01-\uAB06\uAB09-\uAB0E\uAB11-\uAB16\uAB20-\uAB26\uAB28-\uAB2E\uAB30-\uAB5A\uAB5C-\uAB65\uAB70-\uABE2\uAC00-\uD7A3\uD7B0-\uD7C6\uD7CB-\uD7FB\uF900-\uFA6D\uFA70-\uFAD9\uFB00-\uFB06\uFB13-\uFB17\uFB1D\uFB1F-\uFB28\uFB2A-\uFB36\uFB38-\uFB3C\uFB3E\uFB40\uFB41\uFB43\uFB44\uFB46-\uFBB1\uFBD3-\uFD3D\uFD50-\uFD8F\uFD92-\uFDC7\uFDF0-\uFDFB\uFE70-\uFE74\uFE76-\uFEFC\uFF21-\uFF3A\uFF41-\uFF5A\uFF66-\uFFBE\uFFC2-\uFFC7\uFFCA-\uFFCF\uFFD2-\uFFD7\uFFDA-\uFFDC]|\uD800[\uDC00-\uDC0B\uDC0D-\uDC26\uDC28-\uDC3A\uDC3C\uDC3D\uDC3F-\uDC4D\uDC50-\uDC5D\uDC80-\uDCFA\uDD40-\uDD74\uDE80-\uDE9C\uDEA0-\uDED0\uDF00-\uDF1F\uDF30-\uDF4A\uDF50-\uDF75\uDF80-\uDF9D\uDFA0-\uDFC3\uDFC8-\uDFCF\uDFD1-\uDFD5]|\uD801[\uDC00-\uDC9D\uDD00-\uDD27\uDD30-\uDD63\uDE00-\uDF36\uDF40-\uDF55\uDF60-\uDF67]|\uD802[\uDC00-\uDC05\uDC08\uDC0A-\uDC35\uDC37\uDC38\uDC3C\uDC3F-\uDC55\uDC60-\uDC76\uDC80-\uDC9E\uDCE0-\uDCF2\uDCF4\uDCF5\uDD00-\uDD15\uDD20-\uDD39\uDD80-\uDDB7\uDDBE\uDDBF\uDE00\uDE10-\uDE13\uDE15-\uDE17\uDE19-\uDE33\uDE60-\uDE7C\uDE80-\uDE9C\uDEC0-\uDEC7\uDEC9-\uDEE4\uDF00-\uDF35\uDF40-\uDF55\uDF60-\uDF72\uDF80-\uDF91]|\uD803[\uDC00-\uDC48\uDC80-\uDCB2\uDCC0-\uDCF2]|\uD804[\uDC03-\uDC37\uDC83-\uDCAF\uDCD0-\uDCE8\uDD03-\uDD26\uDD50-\uDD72\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    ID_Continue: 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};

function get_full_char(str, pos) {
    var char = str.charAt(pos);
    if (is_surrogate_pair_head(char)) {
        var next = str.charAt(pos + 1);
        if (is_surrogate_pair_tail(next)) {
            return char + next;
        }
    }
    if (is_surrogate_pair_tail(char)) {
        var prev = str.charAt(pos - 1);
        if (is_surrogate_pair_head(prev)) {
            return prev + char;
        }
    }
    return char;
}

function get_full_char_code(str, pos) {
    // https://en.wikipedia.org/wiki/Universal_Character_Set_characters#Surrogates
    if (is_surrogate_pair_head(str.charAt(pos))) {
        return 0x10000 + (str.charCodeAt(pos) - 0xd800 << 10) + str.charCodeAt(pos + 1) - 0xdc00;
    }
    return str.charCodeAt(pos);
}

function get_full_char_length(str) {
    var surrogates = 0;

    for (var i = 0; i < str.length; i++) {
        if (is_surrogate_pair_head(str.charCodeAt(i))) {
            if (is_surrogate_pair_tail(str.charCodeAt(i + 1))) {
                surrogates++;
                i++;
            }
        }
    }

    return str.length - surrogates;
}

function from_char_code(code) {
    // Based on https://github.com/mathiasbynens/String.fromCodePoint/blob/master/fromcodepoint.js
    if (code > 0xFFFF) {
        code -= 0x10000;
        return (String.fromCharCode((code >> 10) + 0xD800) +
            String.fromCharCode((code % 0x400) + 0xDC00));
    }
    return String.fromCharCode(code);
}

function is_surrogate_pair_head(code) {
    if (typeof code === "string")
        code = code.charCodeAt(0);

    return code >= 0xd800 && code <= 0xdbff;
}

function is_surrogate_pair_tail(code) {
    if (typeof code === "string")
        code = code.charCodeAt(0);
    return code >= 0xdc00 && code <= 0xdfff;
}

function is_digit(code) {
    return code >= 48 && code <= 57;
};

function is_identifier(name) {
    if (typeof name !== "string" || RESERVED_WORDS(name))
        return false;

    return true;
};

function is_identifier_start(ch) {
    var code = ch.charCodeAt(0);
    return UNICODE.ID_Start.test(ch) || code == 36 || code == 95;
};

function is_identifier_char(ch) {
    var code = ch.charCodeAt(0);
    return UNICODE.ID_Continue.test(ch)
        || code == 36
        || code == 95
        || code == 8204 // \u200c: zero-width non-joiner <ZWNJ>
        || code == 8205 // \u200d: zero-width joiner <ZWJ> (in my ECMA-262 PDF, this is also 200c)
    ;
};

function is_identifier_string(str){
    return /^[a-z_$][a-z0-9_$]*$/i.test(str);
};

function parse_js_number(num) {
    if (RE_HEX_NUMBER.test(num)) {
        return parseInt(num.substr(2), 16);
    } else if (RE_OCT_NUMBER.test(num)) {
        return parseInt(num.substr(1), 8);
    } else if (RE_ES6_OCT_NUMBER.test(num)) {
        return parseInt(num.substr(2), 8);
    } else if (RE_BIN_NUMBER.test(num)) {
        return parseInt(num.substr(2), 2);
    } else if (RE_DEC_NUMBER.test(num)) {
        return parseFloat(num);
    } else {
        var val = parseFloat(num);
        if (val == num) return val;
    }
};

function JS_Parse_Error(message, filename, line, col, pos) {
    this.message = message;
    this.filename = filename;
    this.line = line;
    this.col = col;
    this.pos = pos;
};
JS_Parse_Error.prototype = Object.create(Error.prototype);
JS_Parse_Error.prototype.constructor = JS_Parse_Error;
JS_Parse_Error.prototype.name = "SyntaxError";
configure_error_stack(JS_Parse_Error);

function js_error(message, filename, line, col, pos) {
    throw new JS_Parse_Error(message, filename, line, col, pos);
};

function is_token(token, type, val) {
    return token.type == type && (val == null || token.value == val);
};

var EX_EOF = {};

function tokenizer($TEXT, filename, html5_comments, shebang) {

    var S = {
        text            : $TEXT,
        filename        : filename,
        pos             : 0,
        tokpos          : 0,
        line            : 1,
        tokline         : 0,
        col             : 0,
        tokcol          : 0,
        newline_before  : false,
        regex_allowed   : false,
        brace_counter   : 0,
        template_braces : [],
        comments_before : [],
        directives      : {},
        directive_stack : []
    };

    function peek() { return get_full_char(S.text, S.pos); };

    function next(signal_eof, in_string) {
        var ch = get_full_char(S.text, S.pos++);
        if (signal_eof && !ch)
            throw EX_EOF;
        if (NEWLINE_CHARS(ch)) {
            S.newline_before = S.newline_before || !in_string;
            ++S.line;
            S.col = 0;
            if (!in_string && ch == "\r" && peek() == "\n") {
                // treat a \r\n sequence as a single \n
                ++S.pos;
                ch = "\n";
            }
        } else {
            if (ch.length > 1) {
                ++S.pos;
                ++S.col;
            }
            ++S.col;
        }
        return ch;
    };

    function forward(i) {
        while (i-- > 0) next();
    };

    function looking_at(str) {
        return S.text.substr(S.pos, str.length) == str;
    };

    function find_eol() {
        var text = S.text;
        for (var i = S.pos, n = S.text.length; i < n; ++i) {
            var ch = text[i];
            if (NEWLINE_CHARS(ch))
                return i;
        }
        return -1;
    };

    function find(what, signal_eof) {
        var pos = S.text.indexOf(what, S.pos);
        if (signal_eof && pos == -1) throw EX_EOF;
        return pos;
    };

    function start_token() {
        S.tokline = S.line;
        S.tokcol = S.col;
        S.tokpos = S.pos;
    };

    var prev_was_dot = false;
    function token(type, value, is_comment) {
        S.regex_allowed = ((type == "operator" && !UNARY_POSTFIX(value)) ||
                           (type == "keyword" && KEYWORDS_BEFORE_EXPRESSION(value)) ||
                           (type == "punc" && PUNC_BEFORE_EXPRESSION(value))) ||
                           (type == "arrow");
        if (type == "punc" && value == ".") {
            prev_was_dot = true;
        } else if (!is_comment) {
            prev_was_dot = false;
        }
        var ret = {
            type    : type,
            value   : value,
            line    : S.tokline,
            col     : S.tokcol,
            pos     : S.tokpos,
            endline : S.line,
            endcol  : S.col,
            endpos  : S.pos,
            nlb     : S.newline_before,
            file    : filename
        };
        if (/^(?:num|string|regexp)$/i.test(type)) {
            ret.raw = $TEXT.substring(ret.pos, ret.endpos);
        }
        if (!is_comment) {
            ret.comments_before = S.comments_before;
            ret.comments_after = S.comments_before = [];
        }
        S.newline_before = false;
        return new AST_Token(ret);
    };

    function skip_whitespace() {
        while (WHITESPACE_CHARS(peek()))
            next();
    };

    function read_while(pred) {
        var ret = "", ch, i = 0;
        while ((ch = peek()) && pred(ch, i++))
            ret += next();
        return ret;
    };

    function parse_error(err) {
        js_error(err, filename, S.tokline, S.tokcol, S.tokpos);
    };

    function read_num(prefix) {
        var has_e = false, after_e = false, has_x = false, has_dot = prefix == ".";
        var num = read_while(function(ch, i){
            var code = ch.charCodeAt(0);
            switch (code) {
              case 98: case 66: // bB
                return (has_x = true); // Can occur in hex sequence, don't return false yet
              case 111: case 79: // oO
              case 120: case 88: // xX
                return has_x ? false : (has_x = true);
              case 101: case 69: // eE
                return has_x ? true : has_e ? false : (has_e = after_e = true);
              case 45: // -
                return after_e || (i == 0 && !prefix);
              case 43: // +
                return after_e;
              case (after_e = false, 46): // .
                return (!has_dot && !has_x && !has_e) ? (has_dot = true) : false;
            }
            return RE_NUM_LITERAL.test(ch);
        });
        if (prefix) num = prefix + num;
        if (RE_OCT_NUMBER.test(num) && next_token.has_directive("use strict")) {
            parse_error("Legacy octal literals are not allowed in strict mode");
        }
        var valid = parse_js_number(num);
        if (!isNaN(valid)) {
            return token("num", valid);
        } else {
            parse_error("Invalid syntax: " + num);
        }
    };

    function read_escaped_char(in_string) {
        var ch = next(true, in_string);
        switch (ch.charCodeAt(0)) {
          case 110 : return "\n";
          case 114 : return "\r";
          case 116 : return "\t";
          case 98  : return "\b";
          case 118 : return "\u000b"; // \v
          case 102 : return "\f";
          case 120 : return String.fromCharCode(hex_bytes(2)); // \x
          case 117 : // \u
            if (peek() == "{") {
                next(true);
                if (peek() === "}")
                    parse_error("Expecting hex-character between {}");
                while (peek() == "0") next(true); // No significance
                var result, length = find("}", true) - S.pos;
                // Avoid 32 bit integer overflow (1 << 32 === 1)
                // We know first character isn't 0 and thus out of range anyway
                if (length > 6 || (result = hex_bytes(length)) > 0x10FFFF) {
                    parse_error("Unicode reference out of bounce");
                }
                next(true);
                return from_char_code(result);
            }
            return String.fromCharCode(hex_bytes(4));
          case 10  : return ""; // newline
          case 13  :            // \r
            if (peek() == "\n") { // DOS newline
                next(true, in_string);
                return "";
            }
        }
        if (ch >= "0" && ch <= "7")
            return read_octal_escape_sequence(ch);
        return ch;
    };

    function read_octal_escape_sequence(ch) {
        // Read
        var p = peek();
        if (p >= "0" && p <= "7") {
            ch += next(true);
            if (ch[0] <= "3" && (p = peek()) >= "0" && p <= "7")
                ch += next(true);
        }

        // Parse
        if (ch === "0") return "\0";
        if (ch.length > 0 && next_token.has_directive("use strict"))
            parse_error("Legacy octal escape sequences are not allowed in strict mode");
        return String.fromCharCode(parseInt(ch, 8));
    }

    function hex_bytes(n) {
        var num = 0;
        for (; n > 0; --n) {
            var digit = parseInt(next(true), 16);
            if (isNaN(digit))
                parse_error("Invalid hex-character pattern in string");
            num = (num << 4) | digit;
        }
        return num;
    };

    var read_string = with_eof_error("Unterminated string constant", function(quote_char){
        var quote = next(), ret = "";
        for (;;) {
            var ch = next(true, true);
            if (ch == "\\") ch = read_escaped_char(true);
            else if (NEWLINE_CHARS(ch)) parse_error("Unterminated string constant");
            else if (ch == quote) break;
            ret += ch;
        }
        var tok = token("string", ret);
        tok.quote = quote_char;
        return tok;
    });

    var read_template_characters = with_eof_error("Unterminated template", function(begin){
        if (begin) {
            S.template_braces.push(S.brace_counter);
        }
        var content = "", raw = "", ch, tok;
        next(true, true);
        while ((ch = next(true, true)) != "`") {
            if (ch == "\r") {
                if (peek() == "\n") ++S.pos;
                ch = "\n";
            } else if (ch == "$" && peek() == "{") {
                next(true, true);
                S.brace_counter++;
                tok = token(begin ? "template_head" : "template_substitution", content);
                tok.begin = begin;
                tok.raw = raw;
                tok.end = false;
                return tok;
            }

            raw += ch;
            if (ch == "\\") {
                var tmp = S.pos;
                ch = read_escaped_char();
                raw += S.text.substr(tmp, S.pos - tmp);
            }

            content += ch;
        }
        S.template_braces.pop();
        tok = token(begin ? "template_head" : "template_substitution", content);
        tok.begin = begin;
        tok.raw = raw;
        tok.end = true;
        return tok;
    });

    function skip_line_comment(type) {
        var regex_allowed = S.regex_allowed;
        var i = find_eol(), ret;
        if (i == -1) {
            ret = S.text.substr(S.pos);
            S.pos = S.text.length;
        } else {
            ret = S.text.substring(S.pos, i);
            S.pos = i;
        }
        S.col = S.tokcol + (S.pos - S.tokpos);
        S.comments_before.push(token(type, ret, true));
        S.regex_allowed = regex_allowed;
        return next_token;
    };

    var skip_multiline_comment = with_eof_error("Unterminated multiline comment", function(){
        var regex_allowed = S.regex_allowed;
        var i = find("*/", true);
        var text = S.text.substring(S.pos, i).replace(/\r\n|\r|\u2028|\u2029/g, '\n');
        // update stream position
        forward(get_full_char_length(text) /* text length doesn't count \r\n as 2 char while S.pos - i does */ + 2);
        S.comments_before.push(token("comment2", text, true));
        S.newline_before = S.newline_before || text.indexOf("\n") >= 0;
        S.regex_allowed = regex_allowed;
        return next_token;
    });

    var read_name = with_eof_error("Unterminated identifier name", function() {
        var name = "", ch, escaped = false, hex;
        var read_escaped_identifier_char = function() {
            escaped = true;
            next();
            if (peek() !== "u") {
                parse_error("Expecting UnicodeEscapeSequence -- uXXXX or u{XXXX}");
            }
            return read_escaped_char();
        }

        // Read first character (ID_Start)
        if ((name = peek()) === "\\") {
            name = read_escaped_identifier_char();
            if (!is_identifier_start(name)) {
                parse_error("First identifier char is an invalid identifier char");
            }
        } else if (is_identifier_start(name)){
            next();
        } else {
            return "";
        }

        // Read ID_Continue
        while ((ch = peek()) != null) {
            if ((ch = peek()) === "\\") {
                ch = read_escaped_identifier_char();
                if (!is_identifier_char(ch)) {
                    parse_error("Invalid escaped identifier char");
                }
            } else {
                if (!is_identifier_char(ch)) {
                    break;
                }
                next();
            }
            name += ch;
        }
        if (RESERVED_WORDS(name) && escaped) {
            parse_error("Escaped characters are not allowed in keywords");
        }
        return name;
    });

    var read_regexp = with_eof_error("Unterminated regular expression", function(source) {
        var prev_backslash = false, ch, in_class = false;
        while ((ch = next(true))) if (NEWLINE_CHARS(ch)) {
            parse_error("Unexpected line terminator");
        } else if (prev_backslash) {
            source += "\\" + ch;
            prev_backslash = false;
        } else if (ch == "[") {
            in_class = true;
            source += ch;
        } else if (ch == "]" && in_class) {
            in_class = false;
            source += ch;
        } else if (ch == "/" && !in_class) {
            break;
        } else if (ch == "\\") {
            prev_backslash = true;
        } else {
            source += ch;
        }
        var mods = read_name();
        try {
            var regexp = new RegExp(source, mods);
            regexp.raw_source = source;
            return token("regexp", regexp);
        } catch(e) {
            parse_error(e.message);
        }
    });

    function read_operator(prefix) {
        function grow(op) {
            if (!peek()) return op;
            var bigger = op + peek();
            if (OPERATORS(bigger)) {
                next();
                return grow(bigger);
            } else {
                return op;
            }
        };
        return token("operator", grow(prefix || next()));
    };

    function handle_slash() {
        next();
        switch (peek()) {
          case "/":
            next();
            return skip_line_comment("comment1");
          case "*":
            next();
            return skip_multiline_comment();
        }
        return S.regex_allowed ? read_regexp("") : read_operator("/");
    };

    function handle_eq_sign() {
        next();
        if (peek() === ">") {
            next();
            return token("arrow", "=>");
        } else {
            return read_operator("=");
        }
    };

    function handle_dot() {
        next();
        if (is_digit(peek().charCodeAt(0))) {
            return read_num(".");
        }
        if (peek() === ".") {
            next();  // Consume second dot
            next();  // Consume third dot
            return token("expand", "...");
        }

        return token("punc", ".");
    };

    function read_word() {
        var word = read_name();
        if (prev_was_dot) return token("name", word);
        return KEYWORDS_ATOM(word) ? token("atom", word)
            : !KEYWORDS(word) ? token("name", word)
            : OPERATORS(word) ? token("operator", word)
            : token("keyword", word);
    };

    function with_eof_error(eof_error, cont) {
        return function(x) {
            try {
                return cont(x);
            } catch(ex) {
                if (ex === EX_EOF) parse_error(eof_error);
                else throw ex;
            }
        };
    };

    function next_token(force_regexp) {
        if (force_regexp != null)
            return read_regexp(force_regexp);
        if (shebang && S.pos == 0 && looking_at("#!")) {
            start_token();
            forward(2);
            skip_line_comment("comment5");
        }
        for (;;) {
            skip_whitespace();
            start_token();
            if (html5_comments) {
                if (looking_at("<!--")) {
                    forward(4);
                    skip_line_comment("comment3");
                    continue;
                }
                if (looking_at("-->") && S.newline_before) {
                    forward(3);
                    skip_line_comment("comment4");
                    continue;
                }
            }
            var ch = peek();
            if (!ch) return token("eof");
            var code = ch.charCodeAt(0);
            switch (code) {
              case 34: case 39: return read_string(ch);
              case 46: return handle_dot();
              case 47: {
                  var tok = handle_slash();
                  if (tok === next_token) continue;
                  return tok;
              }
              case 61: return handle_eq_sign();
              case 96: return read_template_characters(true);
              case 123:
                S.brace_counter++;
                break;
              case 125:
                S.brace_counter--;
                if (S.template_braces.length > 0
                    && S.template_braces[S.template_braces.length - 1] === S.brace_counter)
                    return read_template_characters(false);
                break;
            }
            if (is_digit(code)) return read_num();
            if (PUNC_CHARS(ch)) return token("punc", next());
            if (OPERATOR_CHARS(ch)) return read_operator();
            if (code == 92 || is_identifier_start(ch)) return read_word();
            break;
        }
        parse_error("Unexpected character '" + ch + "'");
    };

    next_token.next = next;
    next_token.peek = peek;

    next_token.context = function(nc) {
        if (nc) S = nc;
        return S;
    };

    next_token.add_directive = function(directive) {
        S.directive_stack[S.directive_stack.length - 1].push(directive);

        if (S.directives[directive] === undefined) {
            S.directives[directive] = 1;
        } else {
            S.directives[directive]++;
        }
    }

    next_token.push_directives_stack = function() {
        S.directive_stack.push([]);
    }

    next_token.pop_directives_stack = function() {
        var directives = S.directive_stack[S.directive_stack.length - 1];

        for (var i = 0; i < directives.length; i++) {
            S.directives[directives[i]]--;
        }

        S.directive_stack.pop();
    }

    next_token.has_directive = function(directive) {
        return S.directives[directive] > 0;
    }

    return next_token;

};

/* -----[ Parser (constants) ]----- */

var UNARY_PREFIX = makePredicate([
    "typeof",
    "void",
    "delete",
    "--",
    "++",
    "!",
    "~",
    "-",
    "+"
]);

var UNARY_POSTFIX = makePredicate([ "--", "++" ]);

var ASSIGNMENT = makePredicate([ "=", "+=", "-=", "/=", "*=", "**=", "%=", ">>=", "<<=", ">>>=", "|=", "^=", "&=" ]);

var PRECEDENCE = (function(a, ret){
    for (var i = 0; i < a.length; ++i) {
        var b = a[i];
        for (var j = 0; j < b.length; ++j) {
            ret[b[j]] = i + 1;
        }
    }
    return ret;
})(
    [
        ["||"],
        ["&&"],
        ["|"],
        ["^"],
        ["&"],
        ["==", "===", "!=", "!=="],
        ["<", ">", "<=", ">=", "in", "instanceof"],
        [">>", "<<", ">>>"],
        ["+", "-"],
        ["*", "/", "%"],
        ["**"]
    ],
    {}
);

var ATOMIC_START_TOKEN = makePredicate([ "atom", "num", "string", "regexp", "name" ]);

/* -----[ Parser ]----- */

function parse($TEXT, options) {

    options = defaults(options, {
        bare_returns   : false,
        ecma           : 8,
        expression     : false,
        filename       : null,
        html5_comments : true,
        shebang        : true,
        strict         : false,
        toplevel       : null,
    }, true);

    var S = {
        input         : (typeof $TEXT == "string"
                         ? tokenizer($TEXT, options.filename,
                                     options.html5_comments, options.shebang)
                         : $TEXT),
        token         : null,
        prev          : null,
        peeked        : null,
        in_function   : 0,
        in_async      : -1,
        in_generator  : -1,
        in_directives : true,
        in_loop       : 0,
        labels        : []
    };

    S.token = next();

    function is(type, value) {
        return is_token(S.token, type, value);
    };

    function peek() { return S.peeked || (S.peeked = S.input()); };

    function next() {
        S.prev = S.token;
        if (S.peeked) {
            S.token = S.peeked;
            S.peeked = null;
        } else {
            S.token = S.input();
        }
        S.in_directives = S.in_directives && (
            S.token.type == "string" || is("punc", ";")
        );
        return S.token;
    };

    function prev() {
        return S.prev;
    };

    function croak(msg, line, col, pos) {
        var ctx = S.input.context();
        js_error(msg,
                 ctx.filename,
                 line != null ? line : ctx.tokline,
                 col != null ? col : ctx.tokcol,
                 pos != null ? pos : ctx.tokpos);
    };

    function token_error(token, msg) {
        croak(msg, token.line, token.col);
    };

    function unexpected(token) {
        if (token == null)
            token = S.token;
        token_error(token, "Unexpected token: " + token.type + " (" + token.value + ")");
    };

    function expect_token(type, val) {
        if (is(type, val)) {
            return next();
        }
        token_error(S.token, "Unexpected token " + S.token.type + " «" + S.token.value + "»" + ", expected " + type + " «" + val + "»");
    };

    function expect(punc) { return expect_token("punc", punc); };

    function has_newline_before(token) {
        return token.nlb || !all(token.comments_before, function(comment) {
            return !comment.nlb;
        });
    }

    function can_insert_semicolon() {
        return !options.strict
            && (is("eof") || is("punc", "}") || has_newline_before(S.token));
    };

    function is_in_generator() {
        return S.in_generator === S.in_function;
    }

    function is_in_async() {
        return S.in_async === S.in_function;
    }

    function semicolon(optional) {
        if (is("punc", ";")) next();
        else if (!optional && !can_insert_semicolon()) unexpected();
    };

    function parenthesised() {
        expect("(");
        var exp = expression(true);
        expect(")");
        return exp;
    };

    function embed_tokens(parser) {
        return function() {
            var start = S.token;
            var expr = parser.apply(null, arguments);
            var end = prev();
            expr.start = start;
            expr.end = end;
            return expr;
        };
    };

    function handle_regexp() {
        if (is("operator", "/") || is("operator", "/=")) {
            S.peeked = null;
            S.token = S.input(S.token.value.substr(1)); // force regexp
        }
    };

    var statement = embed_tokens(function(is_export_default) {
        handle_regexp();
        switch (S.token.type) {
          case "string":
            if (S.in_directives) {
                var token = peek();
                if (S.token.raw.indexOf("\\") == -1
                    && (is_token(token, "punc", ";")
                        || is_token(token, "punc", "}")
                        || has_newline_before(token)
                        || is_token(token, "eof"))) {
                    S.input.add_directive(S.token.value);
                } else {
                    S.in_directives = false;
                }
            }
            var dir = S.in_directives, stat = simple_statement();
            return dir ? new AST_Directive(stat.body) : stat;
          case "template_head":
          case "num":
          case "regexp":
          case "operator":
          case "atom":
            return simple_statement();

          case "name":
            if (S.token.value == "async" && is_token(peek(), "keyword", "function")) {
                next();
                next();
                return function_(AST_Defun, false, true, is_export_default);
            }
            if (S.token.value == "import" && !is_token(peek(), "punc", "(")) {
                next();
                var node = import_();
                semicolon();
                return node;
            }
            return is_token(peek(), "punc", ":")
                ? labeled_statement()
                : simple_statement();

          case "punc":
            switch (S.token.value) {
              case "{":
                return new AST_BlockStatement({
                    start : S.token,
                    body  : block_(),
                    end   : prev()
                });
              case "[":
              case "(":
                return simple_statement();
              case ";":
                S.in_directives = false;
                next();
                return new AST_EmptyStatement();
              default:
                unexpected();
            }

          case "keyword":
            switch (S.token.value) {
              case "break":
                next();
                return break_cont(AST_Break);

              case "continue":
                next();
                return break_cont(AST_Continue);

              case "debugger":
                next();
                semicolon();
                return new AST_Debugger();

              case "do":
                next();
                var body = in_loop(statement);
                expect_token("keyword", "while");
                var condition = parenthesised();
                semicolon(true);
                return new AST_Do({
                    body      : body,
                    condition : condition
                });

              case "while":
                next();
                return new AST_While({
                    condition : parenthesised(),
                    body      : in_loop(statement)
                });

              case "for":
                next();
                return for_();

              case "class":
                next();
                return class_(AST_DefClass);

              case "function":
                next();
                return function_(AST_Defun, false, false, is_export_default);

              case "if":
                next();
                return if_();

              case "return":
                if (S.in_function == 0 && !options.bare_returns)
                    croak("'return' outside of function");
                next();
                var value = null;
                if (is("punc", ";")) {
                    next();
                } else if (!can_insert_semicolon()) {
                    value = expression(true);
                    semicolon();
                }
                return new AST_Return({
                    value: value
                });

              case "switch":
                next();
                return new AST_Switch({
                    expression : parenthesised(),
                    body       : in_loop(switch_body_)
                });

              case "throw":
                next();
                if (has_newline_before(S.token))
                    croak("Illegal newline after 'throw'");
                var value = expression(true);
                semicolon();
                return new AST_Throw({
                    value: value
                });

              case "try":
                next();
                return try_();

              case "var":
                next();
                var node = var_();
                semicolon();
                return node;

              case "let":
                next();
                var node = let_();
                semicolon();
                return node;

              case "const":
                next();
                var node = const_();
                semicolon();
                return node;

              case "with":
                if (S.input.has_directive("use strict")) {
                    croak("Strict mode may not include a with statement");
                }
                next();
                return new AST_With({
                    expression : parenthesised(),
                    body       : statement()
                });

              case "export":
                if (!is_token(peek(), "punc", "(")) {
                    next();
                    return export_();
                }
            }
        }
        unexpected();
    });

    function labeled_statement() {
        var label = as_symbol(AST_Label);
        if (label.name === "await" && is_in_async()) {
            token_error(S.prev, "await cannot be used as label inside async function");
        }
        if (find_if(function(l){ return l.name == label.name }, S.labels)) {
            // ECMA-262, 12.12: An ECMAScript program is considered
            // syntactically incorrect if it contains a
            // LabelledStatement that is enclosed by a
            // LabelledStatement with the same Identifier as label.
            croak("Label " + label.name + " defined twice");
        }
        expect(":");
        S.labels.push(label);
        var stat = statement();
        S.labels.pop();
        if (!(stat instanceof AST_IterationStatement)) {
            // check for `continue` that refers to this label.
            // those should be reported as syntax errors.
            // https://github.com/mishoo/UglifyJS2/issues/287
            label.references.forEach(function(ref){
                if (ref instanceof AST_Continue) {
                    ref = ref.label.start;
                    croak("Continue label `" + label.name + "` refers to non-IterationStatement.",
                          ref.line, ref.col, ref.pos);
                }
            });
        }
        return new AST_LabeledStatement({ body: stat, label: label });
    };

    function simple_statement(tmp) {
        return new AST_SimpleStatement({ body: (tmp = expression(true), semicolon(), tmp) });
    };

    function break_cont(type) {
        var label = null, ldef;
        if (!can_insert_semicolon()) {
            label = as_symbol(AST_LabelRef, true);
        }
        if (label != null) {
            ldef = find_if(function(l){ return l.name == label.name }, S.labels);
            if (!ldef)
                croak("Undefined label " + label.name);
            label.thedef = ldef;
        }
        else if (S.in_loop == 0)
            croak(type.TYPE + " not inside a loop or switch");
        semicolon();
        var stat = new type({ label: label });
        if (ldef) ldef.references.push(stat);
        return stat;
    };

    function for_() {
        expect("(");
        var init = null;
        if (!is("punc", ";")) {
            init =
                is("keyword", "var") ? (next(), var_(true)) :
                is("keyword", "let") ? (next(), let_(true)) :
                is("keyword", "const") ? (next(), const_(true)) :
                                       expression(true, true);
            var is_in = is("operator", "in");
            var is_of = is("name", "of");
            if (is_in || is_of) {
                if (init instanceof AST_Definitions) {
                    if (init.definitions.length > 1)
                        croak("Only one variable declaration allowed in for..in loop", init.start.line, init.start.col, init.start.pos);
                } else if (!(is_assignable(init) || (init = to_destructuring(init)) instanceof AST_Destructuring)) {
                    croak("Invalid left-hand side in for..in loop", init.start.line, init.start.col, init.start.pos);
                }
                next();
                if (is_in) {
                    return for_in(init);
                } else {
                    return for_of(init);
                }
            }
        }
        return regular_for(init);
    };

    function regular_for(init) {
        expect(";");
        var test = is("punc", ";") ? null : expression(true);
        expect(";");
        var step = is("punc", ")") ? null : expression(true);
        expect(")");
        return new AST_For({
            init      : init,
            condition : test,
            step      : step,
            body      : in_loop(statement)
        });
    };

    function for_of(init) {
        var lhs = init instanceof AST_Definitions ? init.definitions[0].name : null;
        var obj = expression(true);
        expect(")");
        return new AST_ForOf({
            init   : init,
            name   : lhs,
            object : obj,
            body   : in_loop(statement)
        });
    };

    function for_in(init) {
        var obj = expression(true);
        expect(")");
        return new AST_ForIn({
            init   : init,
            object : obj,
            body   : in_loop(statement)
        });
    };

    var arrow_function = function(start, argnames, is_async) {
        if (has_newline_before(S.token)) {
            croak("Unexpected newline before arrow (=>)");
        }

        expect_token("arrow", "=>");

        var body = _function_body(is("punc", "{"), false, is_async);

        return new AST_Arrow({
            start    : start,
            end      : body.end,
            async    : is_async,
            argnames : argnames,
            body     : body
        });
    };

    var function_ = function(ctor, is_generator_property, is_async, is_export_default) {
        if (is_generator_property && is_async) croak("generators cannot be async");
        var start = S.token;

        var in_statement = ctor === AST_Defun;
        var is_generator = is("operator", "*");
        if (is_generator) {
            next();
        }

        var name = is("name") ? as_symbol(in_statement ? AST_SymbolDefun : AST_SymbolLambda) : null;
        if (in_statement && !name) {
            if (is_export_default) {
                ctor = AST_Function;
            } else {
                unexpected();
            }
        }

        if (name && ctor !== AST_Accessor && !(name instanceof AST_SymbolDeclaration))
            unexpected(prev());

        var args = [];
        var body = _function_body(true, is_generator || is_generator_property, is_async, name, args);
        return new ctor({
            start : args.start,
            end   : body.end,
            is_generator: is_generator,
            async : is_async,
            name  : name,
            argnames: args,
            body  : body
        });
    };

    function track_used_binding_identifiers(is_parameter, strict) {
        var parameters = {};
        var duplicate = false;
        var default_assignment = false;
        var spread = false;
        var strict_mode = !!strict;
        var tracker = {
            add_parameter: function(token) {
                if (parameters["$" + token.value] !== undefined) {
                    if (duplicate === false) {
                        duplicate = token;
                    }
                    tracker.check_strict();
                } else {
                    parameters["$" + token.value] = true;
                    if (is_parameter) {
                        switch (token.value) {
                          case "arguments":
                          case "eval":
                          case "yield":
                            if (strict_mode) {
                                token_error(token, "Unexpected " + token.value + " identifier as parameter inside strict mode");
                            }
                            break;
                          default:
                            if (RESERVED_WORDS(token.value)) {
                                unexpected();
                            }
                        }
                    }
                }
            },
            mark_default_assignment: function(token) {
                if (default_assignment === false) {
                    default_assignment = token;
                }
            },
            mark_spread: function(token) {
                if (spread === false) {
                    spread = token;
                }
            },
            mark_strict_mode: function() {
                strict_mode = true;
            },
            is_strict: function() {
                return default_assignment !== false || spread !== false || strict_mode
            },
            check_strict: function() {
                if (tracker.is_strict() && duplicate !== false) {
                    token_error(duplicate, "Parameter " + duplicate.value + " was used already");
                }
            }
        };

        return tracker;
    }

    function parameters(params) {
        var start = S.token;
        var used_parameters = track_used_binding_identifiers(true, S.input.has_directive("use strict"));

        expect("(");

        while (!is("punc", ")")) {
            var param = parameter(used_parameters);
            params.push(param);

            if (!is("punc", ")")) {
                expect(",");
                if (is("punc", ")") && options.ecma < 8) unexpected();
            }

            if (param instanceof AST_Expansion) {
                break;
            }
        }

        next();
    }

    function parameter(used_parameters, symbol_type) {
        var param;
        var expand = false;
        if (used_parameters === undefined) {
            used_parameters = track_used_binding_identifiers(true, S.input.has_directive("use strict"));
        }
        if (is("expand", "...")) {
            expand = S.token;
            used_parameters.mark_spread(S.token);
            next();
        }
        param = binding_element(used_parameters, symbol_type);

        if (is("operator", "=") && expand === false) {
            used_parameters.mark_default_assignment(S.token);
            next();
            param = new AST_DefaultAssign({
                start: param.start,
                left: param,
                operator: "=",
                right: expression(false),
                end: S.token
            });
        }

        if (expand !== false) {
            if (!is("punc", ")")) {
                unexpected();
            }
            param = new AST_Expansion({
                start: expand,
                expression: param,
                end: expand
            });
        }
        used_parameters.check_strict();

        return param;
    }

    function binding_element(used_parameters, symbol_type) {
        var elements = [];
        var first = true;
        var is_expand = false;
        var expand_token;
        var first_token = S.token;
        if (used_parameters === undefined) {
            used_parameters = track_used_binding_identifiers(false, S.input.has_directive("use strict"));
        }
        symbol_type = symbol_type === undefined ? AST_SymbolFunarg : symbol_type;
        if (is("punc", "[")) {
            next();
            while (!is("punc", "]")) {
                if (first) {
                    first = false;
                } else {
                    expect(",");
                }

                if (is("expand", "...")) {
                    is_expand = true;
                    expand_token = S.token;
                    used_parameters.mark_spread(S.token);
                    next();
                }
                if (is("punc")) {
                    switch (S.token.value) {
                      case ",":
                        elements.push(new AST_Hole({
                            start: S.token,
                            end: S.token
                        }));
                        continue;
                      case "]": // Trailing comma after last element
                        break;
                      case "[":
                      case "{":
                        elements.push(binding_element(used_parameters, symbol_type));
                        break;
                      default:
                        unexpected();
                    }
                } else if (is("name")) {
                    used_parameters.add_parameter(S.token);
                    elements.push(as_symbol(symbol_type));
                } else {
                    croak("Invalid function parameter");
                }
                if (is("operator", "=") && is_expand === false) {
                    used_parameters.mark_default_assignment(S.token);
                    next();
                    elements[elements.length - 1] = new AST_DefaultAssign({
                        start: elements[elements.length - 1].start,
                        left: elements[elements.length - 1],
                        operator: "=",
                        right: expression(false),
                        end: S.token
                    });
                }
                if (is_expand) {
                    if (!is("punc", "]")) {
                        croak("Rest element must be last element");
                    }
                    elements[elements.length - 1] = new AST_Expansion({
                        start: expand_token,
                        expression: elements[elements.length - 1],
                        end: expand_token
                    });
                }
            }
            expect("]");
            used_parameters.check_strict();
            return new AST_Destructuring({
                start: first_token,
                names: elements,
                is_array: true,
                end: prev()
            });
        } else if (is("punc", "{")) {
            next();
            while (!is("punc", "}")) {
                if (first) {
                    first = false;
                } else {
                    expect(",");
                }
                if (is("expand", "...")) {
                    is_expand = true;
                    expand_token = S.token;
                    used_parameters.mark_spread(S.token);
                    next();
                }
                if (is("name") && (is_token(peek(), "punc") || is_token(peek(), "operator")) && [",", "}", "="].indexOf(peek().value) !== -1) {
                    used_parameters.add_parameter(S.token);
                    var start = prev();
                    var value = as_symbol(symbol_type);
                    if (is_expand) {
                        elements.push(new AST_Expansion({
                            start: expand_token,
                            expression: value,
                            end: value.end,
                        }));
                    } else {
                        elements.push(new AST_ObjectKeyVal({
                            start: start,
                            key: value.name,
                            value: value,
                            end: value.end,
                        }));
                    }
                } else if (is("punc", "}")) {
                    continue; // Allow trailing hole
                } else {
                    var property_token = S.token;
                    var property = as_property_name();
                    if (property === null) {
                        unexpected(prev());
                    } else if (prev().type === "name" && !is("punc", ":")) {
                        elements.push(new AST_ObjectKeyVal({
                            start: prev(),
                            key: property,
                            value: new symbol_type({
                                start: prev(),
                                name: property,
                                end: prev()
                            }),
                            end: prev()
                        }));
                    } else {
                        expect(":");
                        elements.push(new AST_ObjectKeyVal({
                            start: property_token,
                            quote: property_token.quote,
                            key: property,
                            value: binding_element(used_parameters, symbol_type),
                            end: prev()
                        }));
                    }
                }
                if (is_expand) {
                    if (!is("punc", "}")) {
                        croak("Rest element must be last element");
                    }
                }
                else if (is("operator", "=")) {
                    used_parameters.mark_default_assignment(S.token);
                    next();
                    elements[elements.length - 1].value = new AST_DefaultAssign({
                        start: elements[elements.length - 1].value.start,
                        left: elements[elements.length - 1].value,
                        operator: "=",
                        right: expression(false),
                        end: S.token
                    });
                }
            }
            expect("}");
            used_parameters.check_strict();
            return new AST_Destructuring({
                start: first_token,
                names: elements,
                is_array: false,
                end: prev()
            });
        } else if (is("name")) {
            used_parameters.add_parameter(S.token);
            return as_symbol(symbol_type);
        } else {
            croak("Invalid function parameter");
        }
    }

    function params_or_seq_(allow_arrows, maybe_sequence) {
        var spread_token;
        var invalid_sequence;
        var trailing_comma;
        var a = [];
        expect("(");
        while (!is("punc", ")")) {
            if (spread_token) unexpected(spread_token);
            if (is("expand", "...")) {
                spread_token = S.token;
                if (maybe_sequence) invalid_sequence = S.token;
                next();
                a.push(new AST_Expansion({
                    start: prev(),
                    expression: expression(),
                    end: S.token,
                }));
            } else {
                a.push(expression());
            }
            if (!is("punc", ")")) {
                expect(",");
                if (is("punc", ")")) {
                    if (options.ecma < 8) unexpected();
                    trailing_comma = prev();
                    if (maybe_sequence) invalid_sequence = trailing_comma;
                }
            }
        }
        expect(")");
        if (allow_arrows && is("arrow", "=>")) {
            if (spread_token && trailing_comma) unexpected(trailing_comma);
        } else if (invalid_sequence) {
            unexpected(invalid_sequence);
        }
        return a;
    }

    function _function_body(block, generator, is_async, name, args) {
        var loop = S.in_loop;
        var labels = S.labels;
        var current_generator = S.in_generator;
        var current_async = S.in_async;
        ++S.in_function;
        if (generator)
            S.in_generator = S.in_function;
        if (is_async)
            S.in_async = S.in_function;
        if (args) parameters(args);
        if (block)
            S.in_directives = true;
        S.in_loop = 0;
        S.labels = [];
        if (block) {
            S.input.push_directives_stack();
            var a = block_();
            if (name) _verify_symbol(name);
            if (args) args.forEach(_verify_symbol);
            S.input.pop_directives_stack();
        } else {
            var a = expression(false);
        }
        --S.in_function;
        S.in_loop = loop;
        S.labels = labels;
        S.in_generator = current_generator;
        S.in_async = current_async;
        return a;
    }

    function _await_expression() {
        // Previous token must be "await" and not be interpreted as an identifier
        if (!is_in_async()) {
            croak("Unexpected await expression outside async function",
                S.prev.line, S.prev.col, S.prev.pos);
        }
        // the await expression is parsed as a unary expression in Babel
        return new AST_Await({
            expression : maybe_unary(true),
        });
    }

    function _yield_expression() {
        // Previous token must be keyword yield and not be interpret as an identifier
        if (!is_in_generator()) {
            croak("Unexpected yield expression outside generator function",
                S.prev.line, S.prev.col, S.prev.pos);
        }
        var star = false;
        var has_expression = true;

        // Attempt to get expression or star (and then the mandatory expression)
        // behind yield on the same line.
        //
        // If nothing follows on the same line of the yieldExpression,
        // it should default to the value `undefined` for yield to return.
        // In that case, the `undefined` stored as `null` in ast.
        //
        // Note 1: It isn't allowed for yield* to close without an expression
        // Note 2: If there is a nlb between yield and star, it is interpret as
        //         yield <explicit undefined> <inserted automatic semicolon> *
        if (can_insert_semicolon() ||
            (is("punc") && PUNC_AFTER_EXPRESSION(S.token.value))) {
            has_expression = false;

        } else if (is("operator", "*")) {
            star = true;
            next();
        }

        return new AST_Yield({
            is_star    : star,
            expression : has_expression ? expression() : null
        });
    }

    function if_() {
        var cond = parenthesised(), body = statement(), belse = null;
        if (is("keyword", "else")) {
            next();
            belse = statement();
        }
        return new AST_If({
            condition   : cond,
            body        : body,
            alternative : belse
        });
    };

    function block_() {
        expect("{");
        var a = [];
        while (!is("punc", "}")) {
            if (is("eof")) unexpected();
            a.push(statement());
        }
        next();
        return a;
    };

    function switch_body_() {
        expect("{");
        var a = [], cur = null, branch = null, tmp;
        while (!is("punc", "}")) {
            if (is("eof")) unexpected();
            if (is("keyword", "case")) {
                if (branch) branch.end = prev();
                cur = [];
                branch = new AST_Case({
                    start      : (tmp = S.token, next(), tmp),
                    expression : expression(true),
                    body       : cur
                });
                a.push(branch);
                expect(":");
            }
            else if (is("keyword", "default")) {
                if (branch) branch.end = prev();
                cur = [];
                branch = new AST_Default({
                    start : (tmp = S.token, next(), expect(":"), tmp),
                    body  : cur
                });
                a.push(branch);
            }
            else {
                if (!cur) unexpected();
                cur.push(statement());
            }
        }
        if (branch) branch.end = prev();
        next();
        return a;
    };

    function try_() {
        var body = block_(), bcatch = null, bfinally = null;
        if (is("keyword", "catch")) {
            var start = S.token;
            next();
            expect("(");
            var name = parameter(undefined, AST_SymbolCatch);
            expect(")");
            bcatch = new AST_Catch({
                start   : start,
                argname : name,
                body    : block_(),
                end     : prev()
            });
        }
        if (is("keyword", "finally")) {
            var start = S.token;
            next();
            bfinally = new AST_Finally({
                start : start,
                body  : block_(),
                end   : prev()
            });
        }
        if (!bcatch && !bfinally)
            croak("Missing catch/finally blocks");
        return new AST_Try({
            body     : body,
            bcatch   : bcatch,
            bfinally : bfinally
        });
    };

    function vardefs(no_in, kind) {
        var a = [];
        var def;
        for (;;) {
            var sym_type =
                kind === "var" ? AST_SymbolVar :
                kind === "const" ? AST_SymbolConst :
                kind === "let" ? AST_SymbolLet : null;
            if (is("punc", "{") || is("punc", "[")) {
                def = new AST_VarDef({
                    start: S.token,
                    name: binding_element(undefined ,sym_type),
                    value: is("operator", "=") ? (expect_token("operator", "="), expression(false, no_in)) : null,
                    end: prev()
                });
            } else {
                def = new AST_VarDef({
                    start : S.token,
                    name  : as_symbol(sym_type),
                    value : is("operator", "=")
                        ? (next(), expression(false, no_in))
                        : !no_in && kind === "const"
                            ? croak("Missing initializer in const declaration") : null,
                    end   : prev()
                });
                if (def.name.name == "import") croak("Unexpected token: import");
            }
            a.push(def);
            if (!is("punc", ","))
                break;
            next();
        }
        return a;
    };

    var var_ = function(no_in) {
        return new AST_Var({
            start       : prev(),
            definitions : vardefs(no_in, "var"),
            end         : prev()
        });
    };

    var let_ = function(no_in) {
        return new AST_Let({
            start       : prev(),
            definitions : vardefs(no_in, "let"),
            end         : prev()
        });
    };

    var const_ = function(no_in) {
        return new AST_Const({
            start       : prev(),
            definitions : vardefs(no_in, "const"),
            end         : prev()
        });
    };

    var new_ = function(allow_calls) {
        var start = S.token;
        expect_token("operator", "new");
        if (is("punc", ".")) {
            next();
            expect_token("name", "target");
            return subscripts(new AST_NewTarget({
                start : start,
                end   : prev()
            }), allow_calls);
        }
        var newexp = expr_atom(false), args;
        if (is("punc", "(")) {
            next();
            args = expr_list(")", options.ecma >= 8);
        } else {
            args = [];
        }
        var call = new AST_New({
            start      : start,
            expression : newexp,
            args       : args,
            end        : prev()
        });
        mark_pure(call);
        return subscripts(call, allow_calls);
    };

    function as_atom_node() {
        var tok = S.token, ret;
        switch (tok.type) {
          case "name":
            ret = _make_symbol(AST_SymbolRef);
            break;
          case "num":
            ret = new AST_Number({ start: tok, end: tok, value: tok.value });
            break;
          case "string":
            ret = new AST_String({
                start : tok,
                end   : tok,
                value : tok.value,
                quote : tok.quote
            });
            break;
          case "regexp":
            ret = new AST_RegExp({ start: tok, end: tok, value: tok.value });
            break;
          case "atom":
            switch (tok.value) {
              case "false":
                ret = new AST_False({ start: tok, end: tok });
                break;
              case "true":
                ret = new AST_True({ start: tok, end: tok });
                break;
              case "null":
                ret = new AST_Null({ start: tok, end: tok });
                break;
            }
            break;
        }
        next();
        return ret;
    };

    function to_fun_args(ex, _, __, default_seen_above) {
        var insert_default = function(ex, default_value) {
            if (default_value) {
                return new AST_DefaultAssign({
                    start: ex.start,
                    left: ex,
                    operator: "=",
                    right: default_value,
                    end: default_value.end
                });
            }
            return ex;
        }
        if (ex instanceof AST_Object) {
            return insert_default(new AST_Destructuring({
                start: ex.start,
                end: ex.end,
                is_array: false,
                names: ex.properties.map(to_fun_args)
            }), default_seen_above);
        } else if (ex instanceof AST_ObjectKeyVal) {
            ex.value = to_fun_args(ex.value, 0, [ex.key]);
            return insert_default(ex, default_seen_above);
        } else if (ex instanceof AST_Hole) {
            return ex;
        } else if (ex instanceof AST_Destructuring) {
            ex.names = ex.names.map(to_fun_args);
            return insert_default(ex, default_seen_above);
        } else if (ex instanceof AST_SymbolRef) {
            return insert_default(new AST_SymbolFunarg({
                name: ex.name,
                start: ex.start,
                end: ex.end
            }), default_seen_above);
        } else if (ex instanceof AST_Expansion) {
            ex.expression = to_fun_args(ex.expression);
            return insert_default(ex, default_seen_above);
        } else if (ex instanceof AST_Array) {
            return insert_default(new AST_Destructuring({
                start: ex.start,
                end: ex.end,
                is_array: true,
                names: ex.elements.map(to_fun_args)
            }), default_seen_above);
        } else if (ex instanceof AST_Assign) {
            return insert_default(to_fun_args(ex.left, undefined, undefined, ex.right), default_seen_above);
        } else if (ex instanceof AST_DefaultAssign) {
            ex.left = to_fun_args(ex.left, 0, [ex.left]);
            return ex;
        } else {
            croak("Invalid function parameter", ex.start.line, ex.start.col);
        }
    }

    var expr_atom = function(allow_calls, allow_arrows) {
        if (is("operator", "new")) {
            return new_(allow_calls);
        }
        var start = S.token;
        var async = is("name", "async") && as_atom_node();
        if (is("punc")) {
            switch (S.token.value) {
              case "(":
                if (async && !allow_calls) break;
                var exprs = params_or_seq_(allow_arrows, !async);
                if (allow_arrows && is("arrow", "=>")) {
                    return arrow_function(start, exprs.map(to_fun_args), !!async);
                }
                var ex = async ? new AST_Call({
                    expression: async,
                    args: exprs
                }) : exprs.length == 1 ? exprs[0] : new AST_Sequence({
                    expressions: exprs
                });
                if (ex.start) {
                    var len = start.comments_before.length;
                    [].unshift.apply(ex.start.comments_before, start.comments_before);
                    start.comments_before = ex.start.comments_before;
                    start.comments_before_length = len;
                    if (len == 0 && start.comments_before.length > 0) {
                        var comment = start.comments_before[0];
                        if (!comment.nlb) {
                            comment.nlb = start.nlb;
                            start.nlb = false;
                        }
                    }
                    start.comments_after = ex.start.comments_after;
                }
                ex.start = start;
                var end = prev();
                if (ex.end) {
                    end.comments_before = ex.end.comments_before;
                    [].push.apply(ex.end.comments_after, end.comments_after);
                    end.comments_after = ex.end.comments_after;
                }
                ex.end = end;
                if (ex instanceof AST_Call) mark_pure(ex);
                return subscripts(ex, allow_calls);
              case "[":
                return subscripts(array_(), allow_calls);
              case "{":
                return subscripts(object_or_destructuring_(), allow_calls);
            }
            if (!async) unexpected();
        }
        if (allow_arrows && is("name") && is_token(peek(), "arrow")) {
            var param = new AST_SymbolFunarg({
                name: S.token.value,
                start: start,
                end: start,
            });
            next();
            return arrow_function(start, [param], !!async);
        }
        if (is("keyword", "function")) {
            next();
            var func = function_(AST_Function, false, !!async);
            func.start = start;
            func.end = prev();
            return subscripts(func, allow_calls);
        }
        if (async) return subscripts(async, allow_calls);
        if (is("keyword", "class")) {
            next();
            var cls = class_(AST_ClassExpression);
            cls.start = start;
            cls.end = prev();
            return subscripts(cls, allow_calls);
        }
        if (is("template_head")) {
            return subscripts(template_string(), allow_calls);
        }
        if (ATOMIC_START_TOKEN(S.token.type)) {
            return subscripts(as_atom_node(), allow_calls);
        }
        unexpected();
    };

    function template_string() {
        var segments = [], start = S.token;

        segments.push(new AST_TemplateSegment({
            start: S.token,
            raw: S.token.raw,
            value: S.token.value,
            end: S.token
        }));
        while (S.token.end === false) {
            next();
            handle_regexp();
            segments.push(expression(true));

            if (!is_token("template_substitution")) {
                unexpected();
            }

            segments.push(new AST_TemplateSegment({
                start: S.token,
                raw: S.token.raw,
                value: S.token.value,
                end: S.token
            }));
        }
        next();

        return new AST_TemplateString({
            start: start,
            segments: segments,
            end: S.token
        });
    }

    function expr_list(closing, allow_trailing_comma, allow_empty) {
        var first = true, a = [];
        while (!is("punc", closing)) {
            if (first) first = false; else expect(",");
            if (allow_trailing_comma && is("punc", closing)) break;
            if (is("punc", ",") && allow_empty) {
                a.push(new AST_Hole({ start: S.token, end: S.token }));
            } else if (is("expand", "...")) {
                next();
                a.push(new AST_Expansion({start: prev(), expression: expression(),end: S.token}));
            } else {
                a.push(expression(false));
            }
        }
        next();
        return a;
    };

    var array_ = embed_tokens(function() {
        expect("[");
        return new AST_Array({
            elements: expr_list("]", !options.strict, true)
        });
    });

    var create_accessor = embed_tokens(function(is_generator, is_async) {
        return function_(AST_Accessor, is_generator, is_async);
    });

    var object_or_destructuring_ = embed_tokens(function object_or_destructuring_() {
        var start = S.token, first = true, a = [];
        expect("{");
        while (!is("punc", "}")) {
            if (first) first = false; else expect(",");
            if (!options.strict && is("punc", "}"))
                // allow trailing comma
                break;

            start = S.token;
            if (start.type == "expand") {
                next();
                a.push(new AST_Expansion({
                    start: start,
                    expression: expression(false),
                    end: prev(),
                }));
                continue;
            }

            var name = as_property_name();
            var value;

            // Check property and fetch value
            if (!is("punc", ":")) {
                var concise = concise_method_or_getset(name, start);
                if (concise) {
                    a.push(concise);
                    continue;
                }

                value = new AST_SymbolRef({
                    start: prev(),
                    name: name,
                    end: prev()
                });
            } else if (name === null) {
                unexpected(prev());
            } else {
                next(); // `:` - see first condition
                value = expression(false);
            }

            // Check for default value and alter value accordingly if necessary
            if (is("operator", "=")) {
                next();
                value = new AST_Assign({
                    start: start,
                    left: value,
                    operator: "=",
                    right: expression(false),
                    end: prev()
                });
            }

            // Create property
            a.push(new AST_ObjectKeyVal({
                start: start,
                quote: start.quote,
                key: name instanceof AST_Node ? name : "" + name,
                value: value,
                end: prev()
            }));
        }
        next();
        return new AST_Object({ properties: a })
    });

    function class_(KindOfClass) {
        var start, method, class_name, extends_, a = [];

        S.input.push_directives_stack(); // Push directive stack, but not scope stack
        S.input.add_directive("use strict");

        if (S.token.type == "name" && S.token.value != "extends") {
            class_name = as_symbol(KindOfClass === AST_DefClass ? AST_SymbolDefClass : AST_SymbolClass);
        }

        if (KindOfClass === AST_DefClass && !class_name) {
            unexpected();
        }

        if (S.token.value == "extends") {
            next();
            extends_ = expression(true);
        }

        expect("{");

        if (is("punc", ";")) { next(); }  // Leading semicolons are okay in class bodies.
        while (!is("punc", "}")) {
            start = S.token;
            method = concise_method_or_getset(as_property_name(), start, true);
            if (!method) { unexpected(); }
            a.push(method);
            if (is("punc", ";")) { next(); }
        }

        S.input.pop_directives_stack();

        next();

        return new KindOfClass({
            start: start,
            name: class_name,
            extends: extends_,
            properties: a,
            end: prev(),
        });
    }

    function concise_method_or_getset(name, start, is_class) {
        var get_ast = function(name, token) {
            if (typeof name === "string" || typeof name === "number") {
                return new AST_SymbolMethod({
                    start: token,
                    name: "" + name,
                    end: prev()
                });
            } else if (name === null) {
                unexpected();
            }
            return name;
        }
        var is_async = false;
        var is_static = false;
        var is_generator = false;
        var property_token = start;
        if (is_class && name === "static" && !is("punc", "(")) {
            is_static = true;
            property_token = S.token;
            name = as_property_name();
        }
        if (name === "async" && !is("punc", "(") && !is("punc", ",") && !is("punc", "}")) {
            is_async = true;
            property_token = S.token;
            name = as_property_name();
        }
        if (name === null) {
            is_generator = true;
            property_token = S.token;
            name = as_property_name();
            if (name === null) {
                unexpected();
            }
        }
        if (is("punc", "(")) {
            name = get_ast(name, start);
            var node = new AST_ConciseMethod({
                start       : start,
                static      : is_static,
                is_generator: is_generator,
                async       : is_async,
                key         : name,
                quote       : name instanceof AST_SymbolMethod ?
                              property_token.quote : undefined,
                value       : create_accessor(is_generator, is_async),
                end         : prev()
            });
            return node;
        }
        property_token = S.token;
        if (name == "get") {
            if (!is("punc") || is("punc", "[")) {
                name = get_ast(as_property_name(), start);
                return new AST_ObjectGetter({
                    start : start,
                    static: is_static,
                    key   : name,
                    quote : name instanceof AST_SymbolMethod ?
                            property_token.quote : undefined,
                    value : create_accessor(),
                    end   : prev()
                });
            }
        }
        else if (name == "set") {
            if (!is("punc") || is("punc", "[")) {
                name = get_ast(as_property_name(), start);
                return new AST_ObjectSetter({
                    start : start,
                    static: is_static,
                    key   : name,
                    quote : name instanceof AST_SymbolMethod ?
                            property_token.quote : undefined,
                    value : create_accessor(),
                    end   : prev()
                });
            }
        }
    }

    function import_() {
        var start = prev();
        var imported_name;
        var imported_names;
        if (is("name")) {
            imported_name = as_symbol(AST_SymbolImport);
        }

        if (is("punc", ",")) {
            next();
        }

        imported_names = map_names(true);

        if (imported_names || imported_name) {
            expect_token("name", "from");
        }
        var mod_str = S.token;
        if (mod_str.type !== 'string') {
            unexpected();
        }
        next();
        return new AST_Import({
            start: start,
            imported_name: imported_name,
            imported_names: imported_names,
            module_name: new AST_String({
                start: mod_str,
                value: mod_str.value,
                quote: mod_str.quote,
                end: mod_str,
            }),
            end: S.token,
        });
    }

    function map_name(is_import) {
        function make_symbol(type) {
            return new type({
                name: as_property_name(),
                start: prev(),
                end: prev()
            });
        }

        var foreign_type = is_import ? AST_SymbolImportForeign : AST_SymbolExportForeign;
        var type = is_import ? AST_SymbolImport : AST_SymbolExport;
        var start = S.token;
        var foreign_name;
        var name;

        if (is_import) {
            foreign_name = make_symbol(foreign_type);
        } else {
            name = make_symbol(type);
        }
        if (is("name", "as")) {
            next();  // The "as" word
            if (is_import) {
                name = make_symbol(type);
            } else {
                foreign_name = make_symbol(foreign_type);
            }
        } else if (is_import) {
            name = new type(foreign_name);
        } else {
            foreign_name = new foreign_type(name);
        }

        return new AST_NameMapping({
            start: start,
            foreign_name: foreign_name,
            name: name,
            end: prev(),
        })
    }

    function map_nameAsterisk(is_import, name) {
        var foreign_type = is_import ? AST_SymbolImportForeign : AST_SymbolExportForeign;
        var type = is_import ? AST_SymbolImport : AST_SymbolExport;
        var start = S.token;
        var foreign_name;
        var end = prev();

        name = name || new type({
            name: '*',
            start: start,
            end: end,
        });

        foreign_name = new foreign_type({
            name: '*',
            start: start,
            end: end,
        });

        return new AST_NameMapping({
            start: start,
            foreign_name: foreign_name,
            name: name,
            end: end,
        })
    }

    function map_names(is_import) {
        var names;
        if (is("punc", "{")) {
            next();
            names = [];
            while (!is("punc", "}")) {
                names.push(map_name(is_import));
                if (is("punc", ",")) {
                    next();
                }
            }
            next();
        } else if (is("operator", "*")) {
            var name;
            next();
            if (is_import && is("name", "as")) {
                next();  // The "as" word
                name = as_symbol(AST_SymbolImportForeign);
            }
            names = [map_nameAsterisk(is_import, name)];
        }
        return names;
    }

    function export_() {
        var start = S.token;
        var is_default;
        var exported_names;

        if (is("keyword", "default")) {
            is_default = true;
            next();
        } else if (exported_names = map_names(false)) {
            if (is("name", "from")) {
                next();

                var mod_str = S.token;
                if (mod_str.type !== 'string') {
                    unexpected();
                }
                next();

                return new AST_Export({
                    start: start,
                    is_default: is_default,
                    exported_names: exported_names,
                    module_name: new AST_String({
                        start: mod_str,
                        value: mod_str.value,
                        quote: mod_str.quote,
                        end: mod_str,
                    }),
                    end: prev(),
                });
            } else {
                return new AST_Export({
                    start: start,
                    is_default: is_default,
                    exported_names: exported_names,
                    end: prev(),
                });
            }
        }

        var node;
        var exported_value;
        var exported_definition;
        if (is("punc", "{")
            || is_default
                && (is("keyword", "class") || is("keyword", "function"))
                && is_token(peek(), "punc")) {
            exported_value = expression(false);
            semicolon();
        } else if ((node = statement(is_default)) instanceof AST_Definitions && is_default) {
            unexpected(node.start);
        } else if (node instanceof AST_Definitions || node instanceof AST_Lambda || node instanceof AST_DefClass) {
            exported_definition = node;
        } else if (node instanceof AST_SimpleStatement) {
            exported_value = node.body;
        } else {
            unexpected(node.start);
        }

        return new AST_Export({
            start: start,
            is_default: is_default,
            exported_value: exported_value,
            exported_definition: exported_definition,
            end: prev(),
        });
    }

    function as_property_name() {
        var tmp = S.token;
        switch (tmp.type) {
          case "punc":
            if (tmp.value === "[") {
                next();
                var ex = expression(false);
                expect("]");
                return ex;
            } else unexpected(tmp);
          case "operator":
            if (tmp.value === "*") {
                next();
                return null;
            }
            if (["delete", "in", "instanceof", "new", "typeof", "void"].indexOf(tmp.value) === -1) {
                unexpected(tmp);
            }
          case "name":
            if (tmp.value == "yield") {
                if (is_in_generator()) {
                    token_error(tmp, "Yield cannot be used as identifier inside generators");
                } else if (!is_token(peek(), "punc", ":")
                    && !is_token(peek(), "punc", "(")
                    && S.input.has_directive("use strict")) {
                    token_error(tmp, "Unexpected yield identifier inside strict mode");
                }
            }
          case "string":
          case "num":
          case "keyword":
          case "atom":
            next();
            return tmp.value;
          default:
            unexpected(tmp);
        }
    };

    function as_name() {
        var tmp = S.token;
        if (tmp.type != "name") unexpected();
        next();
        return tmp.value;
    };

    function _make_symbol(type) {
        var name = S.token.value;
        return new (name == "this" ? AST_This :
                    name == "super" ? AST_Super :
                    type)({
            name  : String(name),
            start : S.token,
            end   : S.token
        });
    };

    function _verify_symbol(sym) {
        var name = sym.name;
        if (is_in_generator() && name == "yield") {
            token_error(sym.start, "Yield cannot be used as identifier inside generators");
        }
        if (S.input.has_directive("use strict")) {
            if (name == "yield") {
                token_error(sym.start, "Unexpected yield identifier inside strict mode");
            }
            if (sym instanceof AST_SymbolDeclaration && (name == "arguments" || name == "eval")) {
                token_error(sym.start, "Unexpected " + name + " in strict mode");
            }
        }
    }

    function as_symbol(type, noerror) {
        if (!is("name")) {
            if (!noerror) croak("Name expected");
            return null;
        }
        var sym = _make_symbol(type);
        _verify_symbol(sym);
        next();
        return sym;
    };

    function mark_pure(call) {
        var start = call.start;
        var comments = start.comments_before;
        var i = HOP(start, "comments_before_length") ? start.comments_before_length : comments.length;
        while (--i >= 0) {
            var comment = comments[i];
            if (/[@#]__PURE__/.test(comment.value)) {
                call.pure = comment;
                break;
            }
        }
    }

    var subscripts = function(expr, allow_calls) {
        var start = expr.start;
        if (is("punc", ".")) {
            next();
            return subscripts(new AST_Dot({
                start      : start,
                expression : expr,
                property   : as_name(),
                end        : prev()
            }), allow_calls);
        }
        if (is("punc", "[")) {
            next();
            var prop = expression(true);
            expect("]");
            return subscripts(new AST_Sub({
                start      : start,
                expression : expr,
                property   : prop,
                end        : prev()
            }), allow_calls);
        }
        if (allow_calls && is("punc", "(")) {
            next();
            var call = new AST_Call({
                start      : start,
                expression : expr,
                args       : call_args(),
                end        : prev()
            });
            mark_pure(call);
            return subscripts(call, true);
        }
        if (is("template_head")) {
            return subscripts(new AST_PrefixedTemplateString({
                start: start,
                prefix: expr,
                template_string: template_string()
            }), allow_calls);
        }
        return expr;
    };

    var call_args = embed_tokens(function _call_args() {
        var args = [];
        while (!is("punc", ")")) {
            if (is("expand", "...")) {
                next();
                args.push(new AST_Expansion({
                    start: prev(),
                    expression: expression(false)
                }));
            } else {
                args.push(expression(false));
            }
            if (!is("punc", ")")) {
                expect(",");
                if (is("punc", ")") && options.ecma < 8) unexpected();
            }
        }
        next();
        return args;
    });

    var maybe_unary = function(allow_calls, allow_arrows) {
        var start = S.token;
        if (start.type == "name" && start.value == "await") {
            if (is_in_async()) {
                next();
                return _await_expression();
            } else if (S.input.has_directive("use strict")) {
                token_error(S.token, "Unexpected await identifier inside strict mode")
            }
        }
        if (is("operator") && UNARY_PREFIX(start.value)) {
            next();
            handle_regexp();
            var ex = make_unary(AST_UnaryPrefix, start, maybe_unary(allow_calls));
            ex.start = start;
            ex.end = prev();
            return ex;
        }
        var val = expr_atom(allow_calls, allow_arrows);
        while (is("operator") && UNARY_POSTFIX(S.token.value) && !has_newline_before(S.token)) {
            if (val instanceof AST_Arrow) unexpected();
            val = make_unary(AST_UnaryPostfix, S.token, val);
            val.start = start;
            val.end = S.token;
            next();
        }
        return val;
    };

    function make_unary(ctor, token, expr) {
        var op = token.value;
        switch (op) {
          case "++":
          case "--":
            if (!is_assignable(expr))
                croak("Invalid use of " + op + " operator", token.line, token.col, token.pos);
            break;
          case "delete":
            if (expr instanceof AST_SymbolRef && S.input.has_directive("use strict"))
                croak("Calling delete on expression not allowed in strict mode", expr.start.line, expr.start.col, expr.start.pos);
            break;
        }
        return new ctor({ operator: op, expression: expr });
    };

    var expr_op = function(left, min_prec, no_in) {
        var op = is("operator") ? S.token.value : null;
        if (op == "in" && no_in) op = null;
        if (op == "**" && left instanceof AST_UnaryPrefix
            /* unary token in front not allowed - parenthesis required */
            && !is_token(left.start, "punc", "(")
            && left.operator !== "--" && left.operator !== "++")
                unexpected(left.start);
        var prec = op != null ? PRECEDENCE[op] : null;
        if (prec != null && (prec > min_prec || (op === "**" && min_prec === prec))) {
            next();
            var right = expr_op(maybe_unary(true), prec, no_in);
            return expr_op(new AST_Binary({
                start    : left.start,
                left     : left,
                operator : op,
                right    : right,
                end      : right.end
            }), min_prec, no_in);
        }
        return left;
    };

    function expr_ops(no_in) {
        return expr_op(maybe_unary(true, true), 0, no_in);
    };

    var maybe_conditional = function(no_in) {
        var start = S.token;
        var expr = expr_ops(no_in);
        if (is("operator", "?")) {
            next();
            var yes = expression(false);
            expect(":");
            return new AST_Conditional({
                start       : start,
                condition   : expr,
                consequent  : yes,
                alternative : expression(false, no_in),
                end         : prev()
            });
        }
        return expr;
    };

    function is_assignable(expr) {
        return expr instanceof AST_PropAccess || expr instanceof AST_SymbolRef;
    };

    function to_destructuring(node) {
        if (node instanceof AST_Object) {
            node = new AST_Destructuring({
                start: node.start,
                names: node.properties.map(to_destructuring),
                is_array: false,
                end: node.end
            });
        } else if (node instanceof AST_Array) {
            var names = [];

            for (var i = 0; i < node.elements.length; i++) {
                // Only allow expansion as last element
                if (node.elements[i] instanceof AST_Expansion) {
                    if (i + 1 !== node.elements.length) {
                        token_error(node.elements[i].start, "Spread must the be last element in destructuring array");
                    }
                    node.elements[i].expression = to_destructuring(node.elements[i].expression);
                }

                names.push(to_destructuring(node.elements[i]));
            }

            node = new AST_Destructuring({
                start: node.start,
                names: names,
                is_array: true,
                end: node.end
            });
        } else if (node instanceof AST_ObjectProperty) {
            node.value = to_destructuring(node.value);
        } else if (node instanceof AST_Assign) {
            node = new AST_DefaultAssign({
                start: node.start,
                left: node.left,
                operator: "=",
                right: node.right,
                end: node.end
            });
        }
        return node;
    }

    // In ES6, AssignmentExpression can also be an ArrowFunction
    var maybe_assign = function(no_in) {
        var start = S.token;

        if (start.type == "name" && start.value == "yield") {
            if (is_in_generator()) {
                next();
                return _yield_expression();
            } else if (S.input.has_directive("use strict")) {
                token_error(S.token, "Unexpected yield identifier inside strict mode");
            }
        }

        var left = maybe_conditional(no_in);
        var val = S.token.value;

        if (is("operator") && ASSIGNMENT(val)) {
            if (is_assignable(left) || (left = to_destructuring(left)) instanceof AST_Destructuring) {
                next();
                return new AST_Assign({
                    start    : start,
                    left     : left,
                    operator : val,
                    right    : maybe_assign(no_in),
                    end      : prev()
                });
            }
            croak("Invalid assignment");
        }
        return left;
    };

    var expression = function(commas, no_in) {
        var start = S.token;
        var exprs = [];
        while (true) {
            exprs.push(maybe_assign(no_in));
            if (!commas || !is("punc", ",")) break;
            next();
            commas = true;
        }
        return exprs.length == 1 ? exprs[0] : new AST_Sequence({
            start       : start,
            expressions : exprs,
            end         : peek()
        });
    };

    function in_loop(cont) {
        ++S.in_loop;
        var ret = cont();
        --S.in_loop;
        return ret;
    };

    if (options.expression) {
        return expression(true);
    }

    return (function(){
        var start = S.token;
        var body = [];
        S.input.push_directives_stack();
        while (!is("eof"))
            body.push(statement());
        S.input.pop_directives_stack();
        var end = prev();
        var toplevel = options.toplevel;
        if (toplevel) {
            toplevel.body = toplevel.body.concat(body);
            toplevel.end = end;
        } else {
            toplevel = new AST_Toplevel({ start: start, body: body, end: end });
        }
        return toplevel;
    })();

};

/***********************************************************************

  A JavaScript tokenizer / parser / beautifier / compressor.
  https://github.com/mishoo/UglifyJS2

  -------------------------------- (C) ---------------------------------

                           Author: Mihai Bazon
                         <mihai.bazon@gmail.com>
                       http://mihai.bazon.net/blog

  Distributed under the BSD license:

    Copyright 2012 (c) Mihai Bazon <mihai.bazon@gmail.com>

    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions
    are met:

        * Redistributions of source code must retain the above
          copyright notice, this list of conditions and the following
          disclaimer.

        * Redistributions in binary form must reproduce the above
          copyright notice, this list of conditions and the following
          disclaimer in the documentation and/or other materials
          provided with the distribution.

    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER “AS IS” AND ANY
    EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
    IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
    PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER BE
    LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY,
    OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
    PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
    PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
    THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR
    TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
    THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
    SUCH DAMAGE.

 ***********************************************************************/

"use strict";

// Tree transformer helpers.

function TreeTransformer(before, after) {
    TreeWalker.call(this);
    this.before = before;
    this.after = after;
}
TreeTransformer.prototype = new TreeWalker;

(function(undefined){

    function _(node, descend) {
        node.DEFMETHOD("transform", function(tw, in_list){
            var x, y;
            tw.push(this);
            if (tw.before) x = tw.before(this, descend, in_list);
            if (x === undefined) {
                x = this;
                descend(x, tw);
                if (tw.after) {
                    y = tw.after(x, in_list);
                    if (y !== undefined) x = y;
                }
            }
            tw.pop();
            return x;
        });
    };

    function do_list(list, tw) {
        return MAP(list, function(node){
            return node.transform(tw, true);
        });
    };

    _(AST_Node, noop);

    _(AST_LabeledStatement, function(self, tw){
        self.label = self.label.transform(tw);
        self.body = self.body.transform(tw);
    });

    _(AST_SimpleStatement, function(self, tw){
        self.body = self.body.transform(tw);
    });

    _(AST_Block, function(self, tw){
        self.body = do_list(self.body, tw);
    });

    _(AST_DWLoop, function(self, tw){
        self.condition = self.condition.transform(tw);
        self.body = self.body.transform(tw);
    });

    _(AST_For, function(self, tw){
        if (self.init) self.init = self.init.transform(tw);
        if (self.condition) self.condition = self.condition.transform(tw);
        if (self.step) self.step = self.step.transform(tw);
        self.body = self.body.transform(tw);
    });

    _(AST_ForIn, function(self, tw){
        self.init = self.init.transform(tw);
        self.object = self.object.transform(tw);
        self.body = self.body.transform(tw);
    });

    _(AST_With, function(self, tw){
        self.expression = self.expression.transform(tw);
        self.body = self.body.transform(tw);
    });

    _(AST_Exit, function(self, tw){
        if (self.value) self.value = self.value.transform(tw);
    });

    _(AST_LoopControl, function(self, tw){
        if (self.label) self.label = self.label.transform(tw);
    });

    _(AST_If, function(self, tw){
        self.condition = self.condition.transform(tw);
        self.body = self.body.transform(tw);
        if (self.alternative) self.alternative = self.alternative.transform(tw);
    });

    _(AST_Switch, function(self, tw){
        self.expression = self.expression.transform(tw);
        self.body = do_list(self.body, tw);
    });

    _(AST_Case, function(self, tw){
        self.expression = self.expression.transform(tw);
        self.body = do_list(self.body, tw);
    });

    _(AST_Try, function(self, tw){
        self.body = do_list(self.body, tw);
        if (self.bcatch) self.bcatch = self.bcatch.transform(tw);
        if (self.bfinally) self.bfinally = self.bfinally.transform(tw);
    });

    _(AST_Catch, function(self, tw){
        self.argname = self.argname.transform(tw);
        self.body = do_list(self.body, tw);
    });

    _(AST_Definitions, function(self, tw){
        self.definitions = do_list(self.definitions, tw);
    });

    _(AST_VarDef, function(self, tw){
        self.name = self.name.transform(tw);
        if (self.value) self.value = self.value.transform(tw);
    });

    _(AST_Destructuring, function(self, tw) {
        self.names = do_list(self.names, tw);
    });

    _(AST_Lambda, function(self, tw){
        if (self.name) self.name = self.name.transform(tw);
        self.argnames = do_list(self.argnames, tw);
        if (self.body instanceof AST_Node) {
            self.body = self.body.transform(tw);
        } else {
            self.body = do_list(self.body, tw);
        }
    });

    _(AST_Call, function(self, tw){
        self.expression = self.expression.transform(tw);
        self.args = do_list(self.args, tw);
    });

    _(AST_Sequence, function(self, tw){
        self.expressions = do_list(self.expressions, tw);
    });

    _(AST_Dot, function(self, tw){
        self.expression = self.expression.transform(tw);
    });

    _(AST_Sub, function(self, tw){
        self.expression = self.expression.transform(tw);
        self.property = self.property.transform(tw);
    });

    _(AST_Yield, function(self, tw){
        if (self.expression) self.expression = self.expression.transform(tw);
    });

    _(AST_Await, function(self, tw){
        self.expression = self.expression.transform(tw);
    });

    _(AST_Unary, function(self, tw){
        self.expression = self.expression.transform(tw);
    });

    _(AST_Binary, function(self, tw){
        self.left = self.left.transform(tw);
        self.right = self.right.transform(tw);
    });

    _(AST_Conditional, function(self, tw){
        self.condition = self.condition.transform(tw);
        self.consequent = self.consequent.transform(tw);
        self.alternative = self.alternative.transform(tw);
    });

    _(AST_Array, function(self, tw){
        self.elements = do_list(self.elements, tw);
    });

    _(AST_Object, function(self, tw){
        self.properties = do_list(self.properties, tw);
    });

    _(AST_ObjectProperty, function(self, tw){
        if (self.key instanceof AST_Node) {
            self.key = self.key.transform(tw);
        }
        self.value = self.value.transform(tw);
    });

    _(AST_Class, function(self, tw){
        if (self.name) self.name = self.name.transform(tw);
        if (self.extends) self.extends = self.extends.transform(tw);
        self.properties = do_list(self.properties, tw);
    });

    _(AST_Expansion, function(self, tw){
        self.expression = self.expression.transform(tw);
    });

    _(AST_NameMapping, function(self, tw) {
        self.foreign_name = self.foreign_name.transform(tw);
        self.name = self.name.transform(tw);
    });

    _(AST_Import, function(self, tw) {
        if (self.imported_name) self.imported_name = self.imported_name.transform(tw);
        if (self.imported_names) do_list(self.imported_names, tw);
        self.module_name = self.module_name.transform(tw);
    });

    _(AST_Export, function(self, tw) {
        if (self.exported_definition) self.exported_definition = self.exported_definition.transform(tw);
        if (self.exported_value) self.exported_value = self.exported_value.transform(tw);
        if (self.exported_names) do_list(self.exported_names, tw);
        if (self.module_name) self.module_name = self.module_name.transform(tw);
    });

    _(AST_TemplateString, function(self, tw) {
        self.segments = do_list(self.segments, tw);
    });

    _(AST_PrefixedTemplateString, function(self, tw) {
        self.template_string = self.template_string.transform(tw);
    });

})();

/***********************************************************************

  A JavaScript tokenizer / parser / beautifier / compressor.
  https://github.com/mishoo/UglifyJS2

  -------------------------------- (C) ---------------------------------

                           Author: Mihai Bazon
                         <mihai.bazon@gmail.com>
                       http://mihai.bazon.net/blog

  Distributed under the BSD license:

    Copyright 2012 (c) Mihai Bazon <mihai.bazon@gmail.com>

    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions
    are met:

        * Redistributions of source code must retain the above
          copyright notice, this list of conditions and the following
          disclaimer.

        * Redistributions in binary form must reproduce the above
          copyright notice, this list of conditions and the following
          disclaimer in the documentation and/or other materials
          provided with the distribution.

    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER “AS IS” AND ANY
    EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
    IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
    PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER BE
    LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY,
    OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
    PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
    PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
    THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR
    TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
    THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
    SUCH DAMAGE.

 ***********************************************************************/

"use strict";

function SymbolDef(scope, orig, init) {
    this.name = orig.name;
    this.orig = [ orig ];
    this.init = init;
    this.eliminated = 0;
    this.scope = scope;
    this.references = [];
    this.replaced = 0;
    this.global = false;
    this.export = false;
    this.mangled_name = null;
    this.undeclared = false;
    this.id = SymbolDef.next_id++;
};

SymbolDef.next_id = 1;

SymbolDef.prototype = {
    unmangleable: function(options) {
        if (!options) options = {};

        return (this.global && !options.toplevel)
            || this.export
            || this.undeclared
            || (!options.eval && (this.scope.uses_eval || this.scope.uses_with))
            || (options.keep_fnames
                && (this.orig[0] instanceof AST_SymbolLambda
                    || this.orig[0] instanceof AST_SymbolDefun))
            || this.orig[0] instanceof AST_SymbolMethod
            || (options.keep_classnames
                && (this.orig[0] instanceof AST_SymbolClass
                    || this.orig[0] instanceof AST_SymbolDefClass));
    },
    mangle: function(options) {
        var cache = options.cache && options.cache.props;
        if (this.global && cache && cache.has(this.name)) {
            this.mangled_name = cache.get(this.name);
        }
        else if (!this.mangled_name && !this.unmangleable(options)) {
            var s = this.scope;
            var sym = this.orig[0];
            if (options.ie8 && sym instanceof AST_SymbolLambda)
                s = s.parent_scope;
            var def;
            if (def = this.redefined()) {
                this.mangled_name = def.mangled_name || def.name;
            } else
                this.mangled_name = s.next_mangled(options, this);
            if (this.global && cache) {
                cache.set(this.name, this.mangled_name);
            }
        }
    },
    redefined: function() {
        return this.defun && this.defun.variables.get(this.name);
    }
};

AST_Toplevel.DEFMETHOD("figure_out_scope", function(options){
    options = defaults(options, {
        cache: null,
        ie8: false,
        safari10: false,
    });

    // pass 1: setup scope chaining and handle definitions
    var self = this;
    var scope = self.parent_scope = null;
    var labels = new Dictionary();
    var defun = null;
    var in_destructuring = null;
    var for_scopes = [];
    var tw = new TreeWalker(function(node, descend){
        if (node.is_block_scope()) {
            var save_scope = scope;
            node.block_scope = scope = new AST_Scope(node);
            scope.init_scope_vars(save_scope);
            if (!(node instanceof AST_Scope)) {
                scope.uses_with = save_scope.uses_with;
                scope.uses_eval = save_scope.uses_eval;
                scope.directives = save_scope.directives;
            }
            if (options.safari10) {
                if (node instanceof AST_For || node instanceof AST_ForIn) {
                    for_scopes.push(scope);
                }
            }
            descend();
            scope = save_scope;
            return true;
        }
        if (node instanceof AST_Destructuring) {
            in_destructuring = node;  // These don't nest
            descend();
            in_destructuring = null;
            return true;
        }
        if (node instanceof AST_Scope) {
            node.init_scope_vars(scope);
            var save_scope = scope;
            var save_defun = defun;
            var save_labels = labels;
            defun = scope = node;
            labels = new Dictionary();
            descend();
            scope = save_scope;
            defun = save_defun;
            labels = save_labels;
            return true;        // don't descend again in TreeWalker
        }
        if (node instanceof AST_LabeledStatement) {
            var l = node.label;
            if (labels.has(l.name)) {
                throw new Error(string_template("Label {name} defined twice", l));
            }
            labels.set(l.name, l);
            descend();
            labels.del(l.name);
            return true;        // no descend again
        }
        if (node instanceof AST_With) {
            for (var s = scope; s; s = s.parent_scope)
                s.uses_with = true;
            return;
        }
        if (node instanceof AST_Symbol) {
            node.scope = scope;
        }
        if (node instanceof AST_Label) {
            node.thedef = node;
            node.references = [];
        }
        if (node instanceof AST_SymbolLambda) {
            defun.def_function(node, node.name == "arguments" ? undefined : defun);
        }
        else if (node instanceof AST_SymbolDefun) {
            // Careful here, the scope where this should be defined is
            // the parent scope.  The reason is that we enter a new
            // scope when we encounter the AST_Defun node (which is
            // instanceof AST_Scope) but we get to the symbol a bit
            // later.
            mark_export((node.scope = defun.parent_scope.get_defun_scope()).def_function(node, defun), 1);
        }
        else if (node instanceof AST_SymbolClass) {
            mark_export(defun.def_variable(node, defun), 1);
        }
        else if (node instanceof AST_SymbolImport) {
            scope.def_variable(node);
        }
        else if (node instanceof AST_SymbolDefClass) {
            // This deals with the name of the class being available
            // inside the class.
            mark_export((node.scope = defun.parent_scope).def_function(node, defun), 1);
        }
        else if (node instanceof AST_SymbolVar
            || node instanceof AST_SymbolLet
            || node instanceof AST_SymbolConst) {
            var def;
            if (node instanceof AST_SymbolBlockDeclaration) {
                def = scope.def_variable(node, null);
            } else {
                def = defun.def_variable(node, node.TYPE == "SymbolVar" ? null : undefined);
            }
            if (!all(def.orig, function(sym) {
                if (sym === node) return true;
                if (node instanceof AST_SymbolBlockDeclaration) {
                    return sym instanceof AST_SymbolLambda;
                }
                return !(sym instanceof AST_SymbolLet || sym instanceof AST_SymbolConst);
            })) {
                js_error(
                    node.name + " redeclared",
                    node.start.file,
                    node.start.line,
                    node.start.col,
                    node.start.pos
                );
            }
            if (!(node instanceof AST_SymbolFunarg)) mark_export(def, 2);
            def.destructuring = in_destructuring;
            if (defun !== scope) {
                node.mark_enclosed(options);
                var def = scope.find_variable(node);
                if (node.thedef !== def) {
                    node.thedef = def;
                    node.reference(options);
                }
            }
        }
        else if (node instanceof AST_SymbolCatch) {
            scope.def_variable(node).defun = defun;
        }
        else if (node instanceof AST_LabelRef) {
            var sym = labels.get(node.name);
            if (!sym) throw new Error(string_template("Undefined label {name} [{line},{col}]", {
                name: node.name,
                line: node.start.line,
                col: node.start.col
            }));
            node.thedef = sym;
        }
        if (!(scope instanceof AST_Toplevel) && (node instanceof AST_Export || node instanceof AST_Import)) {
            js_error(
                node.TYPE + " statement may only appear at top level",
                node.start.file,
                node.start.line,
                node.start.col,
                node.start.pos
            );
        }

        function mark_export(def, level) {
            if (in_destructuring) {
                var i = 0;
                do {
                    level++;
                } while (tw.parent(i++) !== in_destructuring);
            }
            var node = tw.parent(level);
            def.export = node instanceof AST_Export;
        }
    });
    self.walk(tw);

    // pass 2: find back references and eval
    self.globals = new Dictionary();
    var tw = new TreeWalker(function(node, descend){
        if (node instanceof AST_LoopControl && node.label) {
            node.label.thedef.references.push(node);
            return true;
        }
        if (node instanceof AST_SymbolRef) {
            var name = node.name;
            if (name == "eval" && tw.parent() instanceof AST_Call) {
                for (var s = node.scope; s && !s.uses_eval; s = s.parent_scope) {
                    s.uses_eval = true;
                }
            }
            var sym;
            if (tw.parent() instanceof AST_NameMapping && tw.parent(1).module_name
                || !(sym = node.scope.find_variable(name))) {
                sym = self.def_global(node);
            } else if (sym.scope instanceof AST_Lambda && name == "arguments") {
                sym.scope.uses_arguments = true;
            }
            node.thedef = sym;
            node.reference(options);
            if (node.scope.is_block_scope()
                && !(sym.orig[0] instanceof AST_SymbolBlockDeclaration)) {
                node.scope = node.scope.get_defun_scope();
            }
            return true;
        }
        // ensure mangling works if catch reuses a scope variable
        var def;
        if (node instanceof AST_SymbolCatch && (def = node.definition().redefined())) {
            var s = node.scope;
            while (s) {
                push_uniq(s.enclosed, def);
                if (s === def.scope) break;
                s = s.parent_scope;
            }
        }
    });
    self.walk(tw);

    // pass 3: fix up any scoping issue with IE8
    if (options.ie8) {
        self.walk(new TreeWalker(function(node, descend) {
            if (node instanceof AST_SymbolCatch) {
                var name = node.name;
                var refs = node.thedef.references;
                var scope = node.thedef.defun;
                var def = scope.find_variable(name) || self.globals.get(name) || scope.def_variable(node);
                refs.forEach(function(ref) {
                    ref.thedef = def;
                    ref.reference(options);
                });
                node.thedef = def;
                node.reference(options);
                return true;
            }
        }));
    }

    // pass 4: add symbol definitions to loop scopes
    // Safari/Webkit bug workaround - loop init let variable shadowing argument.
    // https://github.com/mishoo/UglifyJS2/issues/1753
    // https://bugs.webkit.org/show_bug.cgi?id=171041
    if (options.safari10) {
        for (var i = 0; i < for_scopes.length; i++) {
            var scope = for_scopes[i];
            scope.parent_scope.variables.each(function(def) {
                push_uniq(scope.enclosed, def);
            });
        }
    }
});

AST_Toplevel.DEFMETHOD("def_global", function(node){
    var globals = this.globals, name = node.name;
    if (globals.has(name)) {
        return globals.get(name);
    } else {
        var g = new SymbolDef(this, node);
        g.undeclared = true;
        g.global = true;
        globals.set(name, g);
        return g;
    }
});

AST_Scope.DEFMETHOD("init_scope_vars", function(parent_scope){
    this.variables = new Dictionary();  // map name to AST_SymbolVar (variables defined in this scope; includes functions)
    this.functions = new Dictionary();  // map name to AST_SymbolDefun (functions defined in this scope)
    this.uses_with = false;             // will be set to true if this or some nested scope uses the `with` statement
    this.uses_eval = false;             // will be set to true if this or nested scope uses the global `eval`
    this.parent_scope = parent_scope;   // the parent scope
    this.enclosed = [];                 // a list of variables from this or outer scope(s) that are referenced from this or inner scopes
    this.cname = -1;                    // the current index for mangling functions/variables
});

AST_Node.DEFMETHOD("is_block_scope", return_false);
AST_Class.DEFMETHOD("is_block_scope", return_false);
AST_Lambda.DEFMETHOD("is_block_scope", return_false);
AST_Toplevel.DEFMETHOD("is_block_scope", return_false);
AST_SwitchBranch.DEFMETHOD("is_block_scope", return_false);
AST_Block.DEFMETHOD("is_block_scope", return_true);
AST_IterationStatement.DEFMETHOD("is_block_scope", return_true);

AST_Lambda.DEFMETHOD("init_scope_vars", function(){
    AST_Scope.prototype.init_scope_vars.apply(this, arguments);
    this.uses_arguments = false;
    this.def_variable(new AST_SymbolFunarg({
        name: "arguments",
        start: this.start,
        end: this.end
    }));
});

AST_Arrow.DEFMETHOD("init_scope_vars", function(){
    AST_Scope.prototype.init_scope_vars.apply(this, arguments);
    this.uses_arguments = false;
});

AST_Symbol.DEFMETHOD("mark_enclosed", function(options) {
    var def = this.definition();
    var s = this.scope;
    while (s) {
        push_uniq(s.enclosed, def);
        if (options.keep_fnames) {
            s.functions.each(function(d) {
                push_uniq(def.scope.enclosed, d);
            });
        }
        if (s === def.scope) break;
        s = s.parent_scope;
    }
});

AST_Symbol.DEFMETHOD("reference", function(options) {
    this.definition().references.push(this);
    this.mark_enclosed(options);
});

AST_Scope.DEFMETHOD("find_variable", function(name){
    if (name instanceof AST_Symbol) name = name.name;
    return this.variables.get(name)
        || (this.parent_scope && this.parent_scope.find_variable(name));
});

AST_Scope.DEFMETHOD("def_function", function(symbol, init){
    var def = this.def_variable(symbol, init);
    if (!def.init || def.init instanceof AST_Defun) def.init = init;
    this.functions.set(symbol.name, def);
    return def;
});

AST_Scope.DEFMETHOD("def_variable", function(symbol, init){
    var def = this.variables.get(symbol.name);
    if (def) {
        def.orig.push(symbol);
        if (def.init && (def.scope !== symbol.scope || def.init instanceof AST_Function)) {
            def.init = init;
        }
    } else {
        def = new SymbolDef(this, symbol, init);
        this.variables.set(symbol.name, def);
        def.global = !this.parent_scope;
    }
    return symbol.thedef = def;
});

function next_mangled(scope, options) {
    var ext = scope.enclosed;
    out: while (true) {
        var m = base54(++scope.cname);
        if (!is_identifier(m)) continue; // skip over "do"

        // https://github.com/mishoo/UglifyJS2/issues/242 -- do not
        // shadow a name reserved from mangling.
        if (member(m, options.reserved)) continue;

        // we must ensure that the mangled name does not shadow a name
        // from some parent scope that is referenced in this or in
        // inner scopes.
        for (var i = ext.length; --i >= 0;) {
            var sym = ext[i];
            var name = sym.mangled_name || (sym.unmangleable(options) && sym.name);
            if (m == name) continue out;
        }
        return m;
    }
}

AST_Scope.DEFMETHOD("next_mangled", function(options){
    return next_mangled(this, options);
});

AST_Toplevel.DEFMETHOD("next_mangled", function(options){
    var name;
    do {
        name = next_mangled(this, options);
    } while (member(name, this.mangled_names));
    return name;
});

AST_Function.DEFMETHOD("next_mangled", function(options, def){
    // #179, #326
    // in Safari strict mode, something like (function x(x){...}) is a syntax error;
    // a function expression's argument cannot shadow the function expression's name

    var tricky_def = def.orig[0] instanceof AST_SymbolFunarg && this.name && this.name.definition();

    // the function's mangled_name is null when keep_fnames is true
    var tricky_name = tricky_def ? tricky_def.mangled_name || tricky_def.name : null;

    while (true) {
        var name = next_mangled(this, options);
        if (!tricky_name || tricky_name != name)
            return name;
    }
});

AST_Symbol.DEFMETHOD("unmangleable", function(options){
    var def = this.definition();
    return !def || def.unmangleable(options);
});

// labels are always mangleable
AST_Label.DEFMETHOD("unmangleable", return_false);

AST_Symbol.DEFMETHOD("unreferenced", function(){
    return this.definition().references.length == 0
        && !(this.scope.uses_eval || this.scope.uses_with);
});

AST_Symbol.DEFMETHOD("definition", function(){
    return this.thedef;
});

AST_Symbol.DEFMETHOD("global", function(){
    return this.definition().global;
});

AST_Toplevel.DEFMETHOD("_default_mangler_options", function(options) {
    options = defaults(options, {
        eval        : false,
        ie8         : false,
        keep_classnames: false,
        keep_fnames : false,
        reserved    : [],
        toplevel    : false,
    });
    if (!Array.isArray(options.reserved)) options.reserved = [];
    // Never mangle arguments
    push_uniq(options.reserved, "arguments");
    return options;
});

AST_Toplevel.DEFMETHOD("mangle_names", function(options){
    options = this._default_mangler_options(options);

    // We only need to mangle declaration nodes.  Special logic wired
    // into the code generator will display the mangled name if it's
    // present (and for AST_SymbolRef-s it'll use the mangled name of
    // the AST_SymbolDeclaration that it points to).
    var lname = -1;
    var to_mangle = [];

    var mangled_names = this.mangled_names = [];
    if (options.cache) {
        this.globals.each(collect);
        if (options.cache.props) {
            options.cache.props.each(function(mangled_name) {
                push_uniq(mangled_names, mangled_name);
            });
        }
    }

    var tw = new TreeWalker(function(node, descend){
        if (node instanceof AST_LabeledStatement) {
            // lname is incremented when we get to the AST_Label
            var save_nesting = lname;
            descend();
            lname = save_nesting;
            return true;        // don't descend again in TreeWalker
        }
        if (node instanceof AST_Scope) {
            node.variables.each(collect);
            return;
        }
        if (node.is_block_scope()) {
            node.block_scope.variables.each(collect);
            return;
        }
        if (node instanceof AST_Label) {
            var name;
            do name = base54(++lname); while (!is_identifier(name));
            node.mangled_name = name;
            return true;
        }
        if (!options.ie8 && node instanceof AST_SymbolCatch) {
            to_mangle.push(node.definition());
            return;
        }
    });
    this.walk(tw);
    to_mangle.forEach(function(def){ def.mangle(options) });

    function collect(symbol) {
        if (!member(symbol.name, options.reserved)) {
            to_mangle.push(symbol);
        }
    }
});

AST_Toplevel.DEFMETHOD("find_colliding_names", function(options) {
    var cache = options.cache && options.cache.props;
    var avoid = Object.create(null);
    options.reserved.forEach(to_avoid);
    this.globals.each(add_def);
    this.walk(new TreeWalker(function(node) {
        if (node instanceof AST_Scope) node.variables.each(add_def);
        if (node instanceof AST_SymbolCatch) add_def(node.definition());
    }));
    return avoid;

    function to_avoid(name) {
        avoid[name] = true;
    }

    function add_def(def) {
        var name = def.name;
        if (def.global && cache && cache.has(name)) name = cache.get(name);
        else if (!def.unmangleable(options)) return;
        to_avoid(name);
    }
});

AST_Toplevel.DEFMETHOD("expand_names", function(options) {
    base54.reset();
    base54.sort();
    options = this._default_mangler_options(options);
    var avoid = this.find_colliding_names(options);
    var cname = 0;
    this.globals.each(rename);
    this.walk(new TreeWalker(function(node) {
        if (node instanceof AST_Scope) node.variables.each(rename);
        if (node instanceof AST_SymbolCatch) rename(node.definition());
    }));

    function next_name() {
        var name;
        do {
            name = base54(cname++);
        } while (avoid[name] || !is_identifier(name));
        return name;
    }

    function rename(def) {
        if (def.global && options.cache) return;
        if (def.unmangleable(options)) return;
        if (member(def.name, options.reserved)) return;
        var d = def.redefined();
        def.name = d ? d.name : next_name();
        def.orig.forEach(function(sym) {
            sym.name = def.name;
        });
        def.references.forEach(function(sym) {
            sym.name = def.name;
        });
    }
});

AST_Node.DEFMETHOD("tail_node", return_this);
AST_Sequence.DEFMETHOD("tail_node", function() {
    return this.expressions[this.expressions.length - 1];
});

AST_Toplevel.DEFMETHOD("compute_char_frequency", function(options){
    options = this._default_mangler_options(options);
    try {
        AST_Node.prototype.print = function(stream, force_parens) {
            this._print(stream, force_parens);
            if (this instanceof AST_Symbol && !this.unmangleable(options)) {
                base54.consider(this.name, -1);
            } else if (options.properties) {
                if (this instanceof AST_Dot) {
                    base54.consider(this.property, -1);
                } else if (this instanceof AST_Sub) {
                    skip_string(this.property);
                }
            }
        };
        base54.consider(this.print_to_string(), 1);
    } finally {
        AST_Node.prototype.print = AST_Node.prototype._print;
    }
    base54.sort();

    function skip_string(node) {
        if (node instanceof AST_String) {
            base54.consider(node.value, -1);
        } else if (node instanceof AST_Conditional) {
            skip_string(node.consequent);
            skip_string(node.alternative);
        } else if (node instanceof AST_Sequence) {
            skip_string(node.tail_node());
        }
    }
});

var base54 = (function() {
    var leading = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ$_".split("");
    var digits = "0123456789".split("");
    var chars, frequency;
    function reset() {
        frequency = Object.create(null);
        leading.forEach(function(ch) {
            frequency[ch] = 0;
        });
        digits.forEach(function(ch) {
            frequency[ch] = 0;
        });
    }
    base54.consider = function(str, delta) {
        for (var i = str.length; --i >= 0;) {
            frequency[str[i]] += delta;
        }
    };
    function compare(a, b) {
        return frequency[b] - frequency[a];
    }
    base54.sort = function() {
        chars = mergeSort(leading, compare).concat(mergeSort(digits, compare));
    };
    base54.reset = reset;
    reset();
    function base54(num) {
        var ret = "", base = 54;
        num++;
        do {
            num--;
            ret += chars[num % base];
            num = Math.floor(num / base);
            base = 64;
        } while (num > 0);
        return ret;
    };
    return base54;
})();

/***********************************************************************

  A JavaScript tokenizer / parser / beautifier / compressor.
  https://github.com/mishoo/UglifyJS2

  -------------------------------- (C) ---------------------------------

                           Author: Mihai Bazon
                         <mihai.bazon@gmail.com>
                       http://mihai.bazon.net/blog

  Distributed under the BSD license:

    Copyright 2012 (c) Mihai Bazon <mihai.bazon@gmail.com>

    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions
    are met:

        * Redistributions of source code must retain the above
          copyright notice, this list of conditions and the following
          disclaimer.

        * Redistributions in binary form must reproduce the above
          copyright notice, this list of conditions and the following
          disclaimer in the documentation and/or other materials
          provided with the distribution.

    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER “AS IS” AND ANY
    EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
    IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
    PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER BE
    LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY,
    OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
    PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
    PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
    THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR
    TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
    THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
    SUCH DAMAGE.

 ***********************************************************************/

"use strict";

var EXPECT_DIRECTIVE = /^$|[;{][\s\n]*$/;

function is_some_comments(comment) {
    // multiline comment
    return comment.type == "comment2" && /@preserve|@license|@cc_on/i.test(comment.value);
}

function OutputStream(options) {

    var readonly = !options;
    options = defaults(options, {
        ascii_only       : false,
        beautify         : false,
        bracketize       : false,
        comments         : false,
        ecma             : 5,
        ie8              : false,
        indent_level     : 4,
        indent_start     : 0,
        inline_script    : true,
        keep_quoted_props: false,
        max_line_len     : false,
        preamble         : null,
        preserve_line    : false,
        quote_keys       : false,
        quote_style      : 0,
        safari10         : false,
        semicolons       : true,
        shebang          : true,
        shorthand        : undefined,
        source_map       : null,
        webkit           : false,
        width            : 80,
        wrap_iife        : false,
    }, true);

    if (options.shorthand === undefined)
        options.shorthand = options.ecma > 5;

    // Convert comment option to RegExp if neccessary and set up comments filter
    var comment_filter = return_false; // Default case, throw all comments away
    if (options.comments) {
        var comments = options.comments;
        if (typeof options.comments === "string" && /^\/.*\/[a-zA-Z]*$/.test(options.comments)) {
            var regex_pos = options.comments.lastIndexOf("/");
            comments = new RegExp(
                options.comments.substr(1, regex_pos - 1),
                options.comments.substr(regex_pos + 1)
            );
        }
        if (comments instanceof RegExp) {
            comment_filter = function(comment) {
                return comment.type != "comment5" && comments.test(comment.value);
            };
        }
        else if (typeof comments === "function") {
            comment_filter = function(comment) {
                return comment.type != "comment5" && comments(this, comment);
            };
        }
        else if (comments === "some") {
            comment_filter = is_some_comments;
        } else { // NOTE includes "all" option
            comment_filter = return_true;
        }
    }

    var indentation = 0;
    var current_col = 0;
    var current_line = 1;
    var current_pos = 0;
    var OUTPUT = "";

    var to_utf8 = options.ascii_only ? function(str, identifier) {
        if (options.ecma >= 6) {
            str = str.replace(/[\ud800-\udbff][\udc00-\udfff]/g, function(ch) {
                var code = get_full_char_code(ch, 0).toString(16);
                return "\\u{" + code + "}";
            });
        }
        return str.replace(/[\u0000-\u001f\u007f-\uffff]/g, function(ch) {
            var code = ch.charCodeAt(0).toString(16);
            if (code.length <= 2 && !identifier) {
                while (code.length < 2) code = "0" + code;
                return "\\x" + code;
            } else {
                while (code.length < 4) code = "0" + code;
                return "\\u" + code;
            }
        });
    } : function(str) {
        var s = "";
        for (var i = 0, len = str.length; i < len; i++) {
            if (is_surrogate_pair_head(str[i]) && !is_surrogate_pair_tail(str[i + 1])
                || is_surrogate_pair_tail(str[i]) && !is_surrogate_pair_head(str[i - 1])) {
                s += "\\u" + str.charCodeAt(i).toString(16);
            } else {
                s += str[i];
            }
        }
        return s;
    };

    function make_string(str, quote) {
        var dq = 0, sq = 0;
        str = str.replace(/[\\\b\f\n\r\v\t\x22\x27\u2028\u2029\0\ufeff]/g,
          function(s, i){
            switch (s) {
              case '"': ++dq; return '"';
              case "'": ++sq; return "'";
              case "\\": return "\\\\";
              case "\n": return "\\n";
              case "\r": return "\\r";
              case "\t": return "\\t";
              case "\b": return "\\b";
              case "\f": return "\\f";
              case "\x0B": return options.ie8 ? "\\x0B" : "\\v";
              case "\u2028": return "\\u2028";
              case "\u2029": return "\\u2029";
              case "\ufeff": return "\\ufeff";
              case "\0":
                  return /[0-9]/.test(get_full_char(str, i+1)) ? "\\x00" : "\\0";
            }
            return s;
        });
        function quote_single() {
            return "'" + str.replace(/\x27/g, "\\'") + "'";
        }
        function quote_double() {
            return '"' + str.replace(/\x22/g, '\\"') + '"';
        }
        function quote_template() {
            return '`' + str.replace(/`/g, '\\`') + '`';
        }
        str = to_utf8(str);
        if (quote === "`") return quote_template();
        switch (options.quote_style) {
          case 1:
            return quote_single();
          case 2:
            return quote_double();
          case 3:
            return quote == "'" ? quote_single() : quote_double();
          default:
            return dq > sq ? quote_single() : quote_double();
        }
    };

    function encode_string(str, quote) {
        var ret = make_string(str, quote);
        if (options.inline_script) {
            ret = ret.replace(/<\x2fscript([>\/\t\n\f\r ])/gi, "<\\/script$1");
            ret = ret.replace(/\x3c!--/g, "\\x3c!--");
            ret = ret.replace(/--\x3e/g, "--\\x3e");
        }
        return ret;
    };

    function make_name(name) {
        name = name.toString();
        name = to_utf8(name, true);
        return name;
    };

    function make_indent(back) {
        return repeat_string(" ", options.indent_start + indentation - back * options.indent_level);
    };

    /* -----[ beautification/minification ]----- */

    var might_need_space = false;
    var might_need_semicolon = false;
    var might_add_newline = 0;
    var need_newline_indented = false;
    var need_space = false;
    var newline_insert = -1;
    var last = "";
    var mapping_token, mapping_name, mappings = options.source_map && [];

    var do_add_mapping = mappings ? function() {
        mappings.forEach(function(mapping) {
            try {
                options.source_map.add(
                    mapping.token.file,
                    mapping.line, mapping.col,
                    mapping.token.line, mapping.token.col,
                    !mapping.name && mapping.token.type == "name" ? mapping.token.value : mapping.name
                );
            } catch(ex) {
                AST_Node.warn("Couldn't figure out mapping for {file}:{line},{col} ? {cline},{ccol} [{name}]", {
                    file: mapping.token.file,
                    line: mapping.token.line,
                    col: mapping.token.col,
                    cline: mapping.line,
                    ccol: mapping.col,
                    name: mapping.name || ""
                })
            }
        });
        mappings = [];
    } : noop;

    var ensure_line_len = options.max_line_len ? function() {
        if (current_col > options.max_line_len) {
            if (might_add_newline) {
                var left = OUTPUT.slice(0, might_add_newline);
                var right = OUTPUT.slice(might_add_newline);
                if (mappings) {
                    var delta = right.length - current_col;
                    mappings.forEach(function(mapping) {
                        mapping.line++;
                        mapping.col += delta;
                    });
                }
                OUTPUT = left + "\n" + right;
                current_line++;
                current_pos++;
                current_col = right.length;
            }
            if (current_col > options.max_line_len) {
                AST_Node.warn("Output exceeds {max_line_len} characters", options);
            }
        }
        if (might_add_newline) {
            might_add_newline = 0;
            do_add_mapping();
        }
    } : noop;

    var requireSemicolonChars = makePredicate("( [ + * / - , . `");

    function print(str) {
        str = String(str);
        var ch = get_full_char(str, 0);
        var prev = get_full_char(last, last.length - 1);
        if (need_newline_indented && ch) {
            need_newline_indented = false;
            if (ch != "\n") {
                print("\n");
                indent();
            }
        }
        if (need_space && ch) {
            need_space = false;
            if (!/[\s;})]/.test(ch)) {
                space();
            }
        }
        newline_insert = -1;
        var prev = last.charAt(last.length - 1);
        if (might_need_semicolon) {
            might_need_semicolon = false;

            if (prev == ":" && ch == "}" || (!ch || ";}".indexOf(ch) < 0) && prev != ";") {
                if (options.semicolons || requireSemicolonChars(ch)) {
                    OUTPUT += ";";
                    current_col++;
                    current_pos++;
                } else {
                    ensure_line_len();
                    OUTPUT += "\n";
                    current_pos++;
                    current_line++;
                    current_col = 0;

                    if (/^\s+$/.test(str)) {
                        // reset the semicolon flag, since we didn't print one
                        // now and might still have to later
                        might_need_semicolon = true;
                    }
                }

                if (!options.beautify)
                    might_need_space = false;
            }
        }

        if (!options.beautify && options.preserve_line && stack[stack.length - 1]) {
            var target_line = stack[stack.length - 1].start.line;
            while (current_line < target_line) {
                ensure_line_len();
                OUTPUT += "\n";
                current_pos++;
                current_line++;
                current_col = 0;
                might_need_space = false;
            }
        }

        if (might_need_space) {
            if ((is_identifier_char(prev)
                    && (is_identifier_char(ch) || ch == "\\"))
                || (ch == "/" && ch == prev)
                || ((ch == "+" || ch == "-") && ch == last))
            {
                OUTPUT += " ";
                current_col++;
                current_pos++;
            }
            might_need_space = false;
        }

        if (mapping_token) {
            mappings.push({
                token: mapping_token,
                name: mapping_name,
                line: current_line,
                col: current_col
            });
            mapping_token = false;
            if (!might_add_newline) do_add_mapping();
        }

        OUTPUT += str;
        current_pos += str.length;
        var a = str.split(/\r?\n/), n = a.length - 1;
        current_line += n;
        current_col += a[0].length;
        if (n > 0) {
            ensure_line_len();
            current_col = a[n].length;
        }
        last = str;
    };

    var star = function(){
        print("*");
    }

    var space = options.beautify ? function() {
        print(" ");
    } : function() {
        might_need_space = true;
    };

    var indent = options.beautify ? function(half) {
        if (options.beautify) {
            print(make_indent(half ? 0.5 : 0));
        }
    } : noop;

    var with_indent = options.beautify ? function(col, cont) {
        if (col === true) col = next_indent();
        var save_indentation = indentation;
        indentation = col;
        var ret = cont();
        indentation = save_indentation;
        return ret;
    } : function(col, cont) { return cont() };

    var newline = options.beautify ? function() {
        if (newline_insert < 0) return print("\n");
        if (OUTPUT[newline_insert] != "\n") {
            OUTPUT = OUTPUT.slice(0, newline_insert) + "\n" + OUTPUT.slice(newline_insert);
            current_pos++;
            current_line++;
        }
        newline_insert++;
    } : options.max_line_len ? function() {
        ensure_line_len();
        might_add_newline = OUTPUT.length;
    } : noop;

    var semicolon = options.beautify ? function() {
        print(";");
    } : function() {
        might_need_semicolon = true;
    };

    function force_semicolon() {
        might_need_semicolon = false;
        print(";");
    };

    function next_indent() {
        return indentation + options.indent_level;
    };

    function with_block(cont) {
        var ret;
        print("{");
        newline();
        with_indent(next_indent(), function(){
            ret = cont();
        });
        indent();
        print("}");
        return ret;
    };

    function with_parens(cont) {
        print("(");
        //XXX: still nice to have that for argument lists
        //var ret = with_indent(current_col, cont);
        var ret = cont();
        print(")");
        return ret;
    };

    function with_square(cont) {
        print("[");
        //var ret = with_indent(current_col, cont);
        var ret = cont();
        print("]");
        return ret;
    };

    function comma() {
        print(",");
        space();
    };

    function colon() {
        print(":");
        space();
    };

    var add_mapping = mappings ? function(token, name) {
        mapping_token = token;
        mapping_name = name;
    } : noop;

    function get() {
        if (might_add_newline) {
            ensure_line_len();
        }
        return OUTPUT;
    };

    function has_nlb() {
        var index = OUTPUT.lastIndexOf("\n");
        return /^ *$/.test(OUTPUT.slice(index + 1));
    }

    function prepend_comments(node) {
        var self = this;
        var start = node.start;
        if (!start) return;
        if (start.comments_before && start.comments_before._dumped === self) return;
        var comments = start.comments_before;
        if (!comments) {
            comments = start.comments_before = [];
        }
        comments._dumped = self;

        if (node instanceof AST_Exit && node.value) {
            var tw = new TreeWalker(function(node) {
                var parent = tw.parent();
                if (parent instanceof AST_Exit
                    || parent instanceof AST_Binary && parent.left === node
                    || parent.TYPE == "Call" && parent.expression === node
                    || parent instanceof AST_Conditional && parent.condition === node
                    || parent instanceof AST_Dot && parent.expression === node
                    || parent instanceof AST_Sequence && parent.expressions[0] === node
                    || parent instanceof AST_Sub && parent.expression === node
                    || parent instanceof AST_UnaryPostfix) {
                    if (!node.start) return;
                    var text = node.start.comments_before;
                    if (text && text._dumped !== self) {
                        text._dumped = self;
                        comments = comments.concat(text);
                    }
                } else {
                    return true;
                }
            });
            tw.push(node);
            node.value.walk(tw);
        }

        if (current_pos == 0) {
            if (comments.length > 0 && options.shebang && comments[0].type == "comment5") {
                print("#!" + comments.shift().value + "\n");
                indent();
            }
            var preamble = options.preamble;
            if (preamble) {
                print(preamble.replace(/\r\n?|[\n\u2028\u2029]|\s*$/g, "\n"));
            }
        }

        comments = comments.filter(comment_filter, node);
        if (comments.length == 0) return;
        var last_nlb = has_nlb();
        comments.forEach(function(c, i) {
            if (!last_nlb) {
                if (c.nlb) {
                    print("\n");
                    indent();
                    last_nlb = true;
                } else if (i > 0) {
                    space();
                }
            }
            if (/comment[134]/.test(c.type)) {
                print("//" + c.value.replace(/[@#]__PURE__/g, ' ') + "\n");
                indent();
                last_nlb = true;
            } else if (c.type == "comment2") {
                print("/*" + c.value.replace(/[@#]__PURE__/g, ' ') + "*/");
                last_nlb = false;
            }
        });
        if (!last_nlb) {
            if (start.nlb) {
                print("\n");
                indent();
            } else {
                space();
            }
        }
    }

    function append_comments(node, tail) {
        var self = this;
        var token = node.end;
        if (!token) return;
        var comments = token[tail ? "comments_before" : "comments_after"];
        if (!comments || comments._dumped === self) return;
        if (!(node instanceof AST_Statement || all(comments, function(c) {
            return !/comment[134]/.test(c.type);
        }))) return;
        comments._dumped = self;
        var insert = OUTPUT.length;
        comments.filter(comment_filter, node).forEach(function(c, i) {
            need_space = false;
            if (need_newline_indented) {
                print("\n");
                indent();
                need_newline_indented = false;
            } else if (c.nlb && (i > 0 || !has_nlb())) {
                print("\n");
                indent();
            } else if (i > 0 || !tail) {
                space();
            }
            if (/comment[134]/.test(c.type)) {
                print("//" + c.value.replace(/[@#]__PURE__/g, ' '));
                need_newline_indented = true;
            } else if (c.type == "comment2") {
                print("/*" + c.value.replace(/[@#]__PURE__/g, ' ') + "*/");
                need_space = true;
            }
        });
        if (OUTPUT.length > insert) newline_insert = insert;
    }

    var stack = [];
    return {
        get             : get,
        toString        : get,
        indent          : indent,
        indentation     : function() { return indentation },
        current_width   : function() { return current_col - indentation },
        should_break    : function() { return options.width && this.current_width() >= options.width },
        newline         : newline,
        print           : print,
        star            : star,
        space           : space,
        comma           : comma,
        colon           : colon,
        last            : function() { return last },
        semicolon       : semicolon,
        force_semicolon : force_semicolon,
        to_utf8         : to_utf8,
        print_name      : function(name) { print(make_name(name)) },
        print_string    : function(str, quote, escape_directive) {
            var encoded = encode_string(str, quote);
            if (escape_directive === true && encoded.indexOf("\\") === -1) {
                // Insert semicolons to break directive prologue
                if (!EXPECT_DIRECTIVE.test(OUTPUT)) {
                    force_semicolon();
                }
                force_semicolon();
            }
            print(encoded);
        },
        print_template_string_chars: function(str) {
            var encoded = encode_string(str, '`').replace(/\${/g, "\\${");
            return print(encoded.substr(1, encoded.length - 2));
        },
        encode_string   : encode_string,
        next_indent     : next_indent,
        with_indent     : with_indent,
        with_block      : with_block,
        with_parens     : with_parens,
        with_square     : with_square,
        add_mapping     : add_mapping,
        option          : function(opt) { return options[opt] },
        prepend_comments: readonly ? noop : prepend_comments,
        append_comments : readonly || comment_filter === return_false ? noop : append_comments,
        line            : function() { return current_line },
        col             : function() { return current_col },
        pos             : function() { return current_pos },
        push_node       : function(node) { stack.push(node) },
        pop_node        : function() { return stack.pop() },
        parent          : function(n) {
            return stack[stack.length - 2 - (n || 0)];
        }
    };

};

/* -----[ code generators ]----- */

(function(){

    /* -----[ utils ]----- */

    function DEFPRINT(nodetype, generator) {
        nodetype.DEFMETHOD("_codegen", generator);
    };

    var in_directive = false;
    var active_scope = null;
    var use_asm = null;

    AST_Node.DEFMETHOD("print", function(stream, force_parens){
        var self = this, generator = self._codegen;
        if (self instanceof AST_Scope) {
            active_scope = self;
        }
        else if (!use_asm && self instanceof AST_Directive && self.value == "use asm") {
            use_asm = active_scope;
        }
        function doit() {
            stream.prepend_comments(self);
            self.add_source_map(stream);
            generator(self, stream);
            stream.append_comments(self);
        }
        stream.push_node(self);
        if (force_parens || self.needs_parens(stream)) {
            stream.with_parens(doit);
        } else {
            doit();
        }
        stream.pop_node();
        if (self === use_asm) {
            use_asm = null;
        }
    });
    AST_Node.DEFMETHOD("_print", AST_Node.prototype.print);

    AST_Node.DEFMETHOD("print_to_string", function(options){
        var s = OutputStream(options);
        this.print(s);
        return s.get();
    });

    /* -----[ PARENTHESES ]----- */

    function PARENS(nodetype, func) {
        if (Array.isArray(nodetype)) {
            nodetype.forEach(function(nodetype){
                PARENS(nodetype, func);
            });
        } else {
            nodetype.DEFMETHOD("needs_parens", func);
        }
    };

    PARENS(AST_Node, return_false);

    // a function expression needs parens around it when it's provably
    // the first token to appear in a statement.
    PARENS(AST_Function, function(output){
        if (first_in_statement(output)) {
            return true;
        }

        if (output.option('webkit')) {
            var p = output.parent();
            if (p instanceof AST_PropAccess && p.expression === this) {
                return true;
            }
        }

        if (output.option('wrap_iife')) {
            var p = output.parent();
            return p instanceof AST_Call && p.expression === this;
        }

        return false;
    });

    PARENS(AST_Arrow, function(output){
        var p = output.parent();
        return p instanceof AST_PropAccess && p.expression === this;
    });

    // same goes for an object literal, because otherwise it would be
    // interpreted as a block of code.
    PARENS([ AST_ClassExpression, AST_Object ], first_in_statement);

    PARENS(AST_Unary, function(output){
        var p = output.parent();
        return p instanceof AST_PropAccess && p.expression === this
            || p instanceof AST_Call && p.expression === this
            || p instanceof AST_Binary
                && p.operator === "**"
                && this instanceof AST_UnaryPrefix
                && p.left === this
                && this.operator !== "++"
                && this.operator !== "--";
    });

    PARENS(AST_Await, function(output){
        var p = output.parent();
        return p instanceof AST_PropAccess && p.expression === this
            || p instanceof AST_Call && p.expression === this
            || output.option("safari10") && p instanceof AST_UnaryPrefix;
    });

    PARENS(AST_Sequence, function(output){
        var p = output.parent();
        return p instanceof AST_Call                          // (foo, bar)() or foo(1, (2, 3), 4)
            || p instanceof AST_Unary                         // !(foo, bar, baz)
            || p instanceof AST_Binary                        // 1 + (2, 3) + 4 ==> 8
            || p instanceof AST_VarDef                        // var a = (1, 2), b = a + a; ==> b == 4
            || p instanceof AST_PropAccess                    // (1, {foo:2}).foo or (1, {foo:2})["foo"] ==> 2
            || p instanceof AST_Array                         // [ 1, (2, 3), 4 ] ==> [ 1, 3, 4 ]
            || p instanceof AST_ObjectProperty                // { foo: (1, 2) }.foo ==> 2
            || p instanceof AST_Conditional                   /* (false, true) ? (a = 10, b = 20) : (c = 30)
                                                               * ==> 20 (side effect, set a := 10 and b := 20) */
            || p instanceof AST_Arrow                         // x => (x, x)
            || p instanceof AST_DefaultAssign                 // x => (x = (0, function(){}))
            || p instanceof AST_Expansion                     // [...(a, b)]
            || p instanceof AST_ForOf && this === p.object    // for (e of (foo, bar)) {}
            || p instanceof AST_Yield                         // yield (foo, bar)
        ;
    });

    PARENS(AST_Binary, function(output){
        var p = output.parent();
        // (foo && bar)()
        if (p instanceof AST_Call && p.expression === this)
            return true;
        // typeof (foo && bar)
        if (p instanceof AST_Unary)
            return true;
        // (foo && bar)["prop"], (foo && bar).prop
        if (p instanceof AST_PropAccess && p.expression === this)
            return true;
        // this deals with precedence: 3 * (2 + 1)
        if (p instanceof AST_Binary) {
            var po = p.operator, pp = PRECEDENCE[po];
            var so = this.operator, sp = PRECEDENCE[so];
            if (pp > sp
                || (pp == sp
                    && this === p.right)) {
                return true;
            }
        }
    });

    PARENS(AST_Yield, function(output){
        var p = output.parent();
        // (yield 1) + (yield 2)
        // a = yield 3
        if (p instanceof AST_Binary && p.operator !== "=")
            return true;
        // (yield 1)()
        // new (yield 1)()
        if (p instanceof AST_Call && p.expression === this)
            return true;
        // (yield 1) ? yield 2 : yield 3
        if (p instanceof AST_Conditional && p.condition === this)
            return true;
        // -(yield 4)
        if (p instanceof AST_Unary)
            return true;
        // (yield x).foo
        // (yield x)['foo']
        if (p instanceof AST_PropAccess && p.expression === this)
            return true;
    });

    PARENS(AST_PropAccess, function(output){
        var p = output.parent();
        if (p instanceof AST_New && p.expression === this) {
            // i.e. new (foo.bar().baz)
            //
            // if there's one call into this subtree, then we need
            // parens around it too, otherwise the call will be
            // interpreted as passing the arguments to the upper New
            // expression.
            var parens = false;
            this.walk(new TreeWalker(function(node) {
                if (parens || node instanceof AST_Scope) return true;
                if (node instanceof AST_Call) {
                    parens = true;
                    return true;
                }
            }));
            return parens;
        }
    });

    PARENS(AST_Call, function(output){
        var p = output.parent(), p1;
        if (p instanceof AST_New && p.expression === this)
            return true;

        // workaround for Safari bug.
        // https://bugs.webkit.org/show_bug.cgi?id=123506
        return this.expression instanceof AST_Function
            && p instanceof AST_PropAccess
            && p.expression === this
            && (p1 = output.parent(1)) instanceof AST_Assign
            && p1.left === p;
    });

    PARENS(AST_New, function(output){
        var p = output.parent();
        if (!need_constructor_parens(this, output)
            && (p instanceof AST_PropAccess // (new Date).getTime(), (new Date)["getTime"]()
                || p instanceof AST_Call && p.expression === this)) // (new foo)(bar)
            return true;
    });

    PARENS(AST_Number, function(output){
        var p = output.parent();
        if (p instanceof AST_PropAccess && p.expression === this) {
            var value = this.getValue();
            if (value < 0 || /^0/.test(make_num(value))) {
                return true;
            }
        }
    });

    PARENS([ AST_Assign, AST_Conditional ], function(output){
        var p = output.parent();
        // !(a = false) ? true
        if (p instanceof AST_Unary)
            return true;
        // 1 + (a = 2) + 3 ? 6, side effect setting a = 2
        if (p instanceof AST_Binary && !(p instanceof AST_Assign))
            return true;
        // (a = func)() —or— new (a = Object)()
        if (p instanceof AST_Call && p.expression === this)
            return true;
        // (a = foo) ? bar : baz
        if (p instanceof AST_Conditional && p.condition === this)
            return true;
        // (a = foo)["prop"] —or— (a = foo).prop
        if (p instanceof AST_PropAccess && p.expression === this)
            return true;
        // ({a, b} = {a: 1, b: 2}), a destructuring assignment
        if (this instanceof AST_Assign && this.left instanceof AST_Destructuring && this.left.is_array === false)
            return true;
    });

    /* -----[ PRINTERS ]----- */

    DEFPRINT(AST_Directive, function(self, output){
        output.print_string(self.value, self.quote);
        output.semicolon();
    });

    DEFPRINT(AST_Expansion, function (self, output) {
        output.print('...');
        self.expression.print(output);
    });

    DEFPRINT(AST_Destructuring, function (self, output) {
        output.print(self.is_array ? "[" : "{");
        var len = self.names.length;
        self.names.forEach(function (name, i) {
            if (i > 0) output.comma();
            name.print(output);
            // If the final element is a hole, we need to make sure it
            // doesn't look like a trailing comma, by inserting an actual
            // trailing comma.
            if (i == len - 1 && name instanceof AST_Hole) output.comma();
        });
        output.print(self.is_array ? "]" : "}");
    });

    DEFPRINT(AST_Debugger, function(self, output){
        output.print("debugger");
        output.semicolon();
    });

    /* -----[ statements ]----- */

    function display_body(body, is_toplevel, output, allow_directives) {
        var last = body.length - 1;
        in_directive = allow_directives;
        body.forEach(function(stmt, i){
            if (in_directive === true && !(stmt instanceof AST_Directive ||
                stmt instanceof AST_EmptyStatement ||
                (stmt instanceof AST_SimpleStatement && stmt.body instanceof AST_String)
            )) {
                in_directive = false;
            }
            if (!(stmt instanceof AST_EmptyStatement)) {
                output.indent();
                stmt.print(output);
                if (!(i == last && is_toplevel)) {
                    output.newline();
                    if (is_toplevel) output.newline();
                }
            }
            if (in_directive === true &&
                stmt instanceof AST_SimpleStatement &&
                stmt.body instanceof AST_String
            ) {
                in_directive = false;
            }
        });
        in_directive = false;
    };

    AST_StatementWithBody.DEFMETHOD("_do_print_body", function(output){
        force_statement(this.body, output);
    });

    DEFPRINT(AST_Statement, function(self, output){
        self.body.print(output);
        output.semicolon();
    });
    DEFPRINT(AST_Toplevel, function(self, output){
        display_body(self.body, true, output, true);
        output.print("");
    });
    DEFPRINT(AST_LabeledStatement, function(self, output){
        self.label.print(output);
        output.colon();
        self.body.print(output);
    });
    DEFPRINT(AST_SimpleStatement, function(self, output){
        self.body.print(output);
        output.semicolon();
    });
    function print_bracketed(self, output, allow_directives) {
        if (self.body.length > 0) {
            output.with_block(function() {
                display_body(self.body, false, output, allow_directives);
            });
        } else {
            output.print("{");
            output.with_indent(output.next_indent(), function() {
                output.append_comments(self, true);
            });
            output.print("}");
        }
    };
    DEFPRINT(AST_BlockStatement, function(self, output){
        print_bracketed(self, output);
    });
    DEFPRINT(AST_EmptyStatement, function(self, output){
        output.semicolon();
    });
    DEFPRINT(AST_Do, function(self, output){
        output.print("do");
        output.space();
        make_block(self.body, output);
        output.space();
        output.print("while");
        output.space();
        output.with_parens(function(){
            self.condition.print(output);
        });
        output.semicolon();
    });
    DEFPRINT(AST_While, function(self, output){
        output.print("while");
        output.space();
        output.with_parens(function(){
            self.condition.print(output);
        });
        output.space();
        self._do_print_body(output);
    });
    DEFPRINT(AST_For, function(self, output){
        output.print("for");
        output.space();
        output.with_parens(function(){
            if (self.init) {
                if (self.init instanceof AST_Definitions) {
                    self.init.print(output);
                } else {
                    parenthesize_for_noin(self.init, output, true);
                }
                output.print(";");
                output.space();
            } else {
                output.print(";");
            }
            if (self.condition) {
                self.condition.print(output);
                output.print(";");
                output.space();
            } else {
                output.print(";");
            }
            if (self.step) {
                self.step.print(output);
            }
        });
        output.space();
        self._do_print_body(output);
    });
    DEFPRINT(AST_ForIn, function(self, output){
        output.print("for");
        output.space();
        output.with_parens(function(){
            self.init.print(output);
            output.space();
            output.print(self instanceof AST_ForOf ? "of" : "in");
            output.space();
            self.object.print(output);
        });
        output.space();
        self._do_print_body(output);
    });
    DEFPRINT(AST_With, function(self, output){
        output.print("with");
        output.space();
        output.with_parens(function(){
            self.expression.print(output);
        });
        output.space();
        self._do_print_body(output);
    });

    /* -----[ functions ]----- */
    AST_Lambda.DEFMETHOD("_do_print", function(output, nokeyword){
        var self = this;
        if (!nokeyword) {
            if (self.async) {
                output.print("async");
                output.space();
            }
            output.print("function");
            if (self.is_generator) {
                output.star();
            }
            if (self.name) {
                output.space();
            }
        }
        if (self.name instanceof AST_Symbol) {
            self.name.print(output);
        } else if (nokeyword && self.name instanceof AST_Node) {
            output.with_square(function() {
                self.name.print(output); // Computed method name
            });
        }
        output.with_parens(function(){
            self.argnames.forEach(function(arg, i){
                if (i) output.comma();
                arg.print(output);
            });
        });
        output.space();
        print_bracketed(self, output, true);
    });
    DEFPRINT(AST_Lambda, function(self, output){
        self._do_print(output);
    });

    DEFPRINT(AST_PrefixedTemplateString, function(self, output) {
        self.prefix.print(output);
        self.template_string.print(output);
    });
    DEFPRINT(AST_TemplateString, function(self, output) {
        var is_tagged = output.parent() instanceof AST_PrefixedTemplateString;

        output.print("`");
        for (var i = 0; i < self.segments.length; i++) {
            if (!(self.segments[i] instanceof AST_TemplateSegment)) {
                output.print("${");
                self.segments[i].print(output);
                output.print("}");
            } else if (is_tagged) {
                output.print(self.segments[i].raw);
            } else {
                output.print_template_string_chars(self.segments[i].value);
            }
        }
        output.print("`");
    });

    AST_Arrow.DEFMETHOD("_do_print", function(output){
        var self = this;
        var parent = output.parent();
        var needs_parens = parent instanceof AST_Binary ||
            parent instanceof AST_Unary ||
            (parent instanceof AST_Call && self === parent.expression);
        if (needs_parens) { output.print("(") }
        if (self.async) {
            output.print("async");
            output.space();
        }
        if (self.argnames.length === 1 && self.argnames[0] instanceof AST_Symbol) {
            self.argnames[0].print(output);
        } else {
            output.with_parens(function(){
                self.argnames.forEach(function(arg, i){
                    if (i) output.comma();
                    arg.print(output);
                });
            });
        }
        output.space();
        output.print('=>');
        output.space();
        if (self.body instanceof AST_Node) {
            self.body.print(output);
        } else {
            print_bracketed(self, output);
        }
        if (needs_parens) { output.print(")") }
    });

    /* -----[ exits ]----- */
    AST_Exit.DEFMETHOD("_do_print", function(output, kind){
        output.print(kind);
        if (this.value) {
            output.space();
            this.value.print(output);
        }
        output.semicolon();
    });
    DEFPRINT(AST_Return, function(self, output){
        self._do_print(output, "return");
    });
    DEFPRINT(AST_Throw, function(self, output){
        self._do_print(output, "throw");
    });

    /* -----[ yield ]----- */

    DEFPRINT(AST_Yield, function(self, output){
        var star = self.is_star ? "*" : "";
        output.print("yield" + star);
        if (self.expression) {
            output.space();
            self.expression.print(output);
        }
    });

    DEFPRINT(AST_Await, function(self, output){
        output.print("await");
        output.space();
        var e = self.expression;
        var parens = !(
               e instanceof AST_Call
            || e instanceof AST_SymbolRef
            || e instanceof AST_PropAccess
            || e instanceof AST_Unary
            || e instanceof AST_Constant
        );
        if (parens) output.print("(");
        self.expression.print(output);
        if (parens) output.print(")");
    });

    /* -----[ loop control ]----- */
    AST_LoopControl.DEFMETHOD("_do_print", function(output, kind){
        output.print(kind);
        if (this.label) {
            output.space();
            this.label.print(output);
        }
        output.semicolon();
    });
    DEFPRINT(AST_Break, function(self, output){
        self._do_print(output, "break");
    });
    DEFPRINT(AST_Continue, function(self, output){
        self._do_print(output, "continue");
    });

    /* -----[ if ]----- */
    function make_then(self, output) {
        var b = self.body;
        if (output.option("bracketize")
            || output.option("ie8") && b instanceof AST_Do)
            return make_block(b, output);
        // The squeezer replaces "block"-s that contain only a single
        // statement with the statement itself; technically, the AST
        // is correct, but this can create problems when we output an
        // IF having an ELSE clause where the THEN clause ends in an
        // IF *without* an ELSE block (then the outer ELSE would refer
        // to the inner IF).  This function checks for this case and
        // adds the block brackets if needed.
        if (!b) return output.force_semicolon();
        while (true) {
            if (b instanceof AST_If) {
                if (!b.alternative) {
                    make_block(self.body, output);
                    return;
                }
                b = b.alternative;
            }
            else if (b instanceof AST_StatementWithBody) {
                b = b.body;
            }
            else break;
        }
        force_statement(self.body, output);
    };
    DEFPRINT(AST_If, function(self, output){
        output.print("if");
        output.space();
        output.with_parens(function(){
            self.condition.print(output);
        });
        output.space();
        if (self.alternative) {
            make_then(self, output);
            output.space();
            output.print("else");
            output.space();
            if (self.alternative instanceof AST_If)
                self.alternative.print(output);
            else
                force_statement(self.alternative, output);
        } else {
            self._do_print_body(output);
        }
    });

    /* -----[ switch ]----- */
    DEFPRINT(AST_Switch, function(self, output){
        output.print("switch");
        output.space();
        output.with_parens(function(){
            self.expression.print(output);
        });
        output.space();
        var last = self.body.length - 1;
        if (last < 0) output.print("{}");
        else output.with_block(function(){
            self.body.forEach(function(branch, i){
                output.indent(true);
                branch.print(output);
                if (i < last && branch.body.length > 0)
                    output.newline();
            });
        });
    });
    AST_SwitchBranch.DEFMETHOD("_do_print_body", function(output){
        output.newline();
        this.body.forEach(function(stmt){
            output.indent();
            stmt.print(output);
            output.newline();
        });
    });
    DEFPRINT(AST_Default, function(self, output){
        output.print("default:");
        self._do_print_body(output);
    });
    DEFPRINT(AST_Case, function(self, output){
        output.print("case");
        output.space();
        self.expression.print(output);
        output.print(":");
        self._do_print_body(output);
    });

    /* -----[ exceptions ]----- */
    DEFPRINT(AST_Try, function(self, output){
        output.print("try");
        output.space();
        print_bracketed(self, output);
        if (self.bcatch) {
            output.space();
            self.bcatch.print(output);
        }
        if (self.bfinally) {
            output.space();
            self.bfinally.print(output);
        }
    });
    DEFPRINT(AST_Catch, function(self, output){
        output.print("catch");
        output.space();
        output.with_parens(function(){
            self.argname.print(output);
        });
        output.space();
        print_bracketed(self, output);
    });
    DEFPRINT(AST_Finally, function(self, output){
        output.print("finally");
        output.space();
        print_bracketed(self, output);
    });

    /* -----[ var/const ]----- */
    AST_Definitions.DEFMETHOD("_do_print", function(output, kind){
        output.print(kind);
        output.space();
        this.definitions.forEach(function(def, i){
            if (i) output.comma();
            def.print(output);
        });
        var p = output.parent();
        var in_for = p instanceof AST_For || p instanceof AST_ForIn;
        var avoid_semicolon = in_for && p.init === this;
        if (!avoid_semicolon)
            output.semicolon();
    });
    DEFPRINT(AST_Let, function(self, output){
        self._do_print(output, "let");
    });
    DEFPRINT(AST_Var, function(self, output){
        self._do_print(output, "var");
    });
    DEFPRINT(AST_Const, function(self, output){
        self._do_print(output, "const");
    });
    DEFPRINT(AST_Import, function(self, output) {
        output.print("import");
        output.space();
        if (self.imported_name) {
            self.imported_name.print(output);
        }
        if (self.imported_name && self.imported_names) {
            output.print(",");
            output.space();
        }
        if (self.imported_names) {
            if (self.imported_names.length === 1 && self.imported_names[0].foreign_name.name === "*") {
                self.imported_names[0].print(output);
            } else {
                output.print("{");
                self.imported_names.forEach(function (name_import, i) {
                    output.space();
                    name_import.print(output);
                    if (i < self.imported_names.length - 1) {
                        output.print(",");
                    }
                });
                output.space();
                output.print("}");
            }
        }
        if (self.imported_name || self.imported_names) {
            output.space();
            output.print("from")
            output.space();
        }
        self.module_name.print(output);
        output.semicolon();
    });

    DEFPRINT(AST_NameMapping, function(self, output) {
        var is_import = output.parent() instanceof AST_Import;
        var definition = self.name.definition();
        var names_are_different =
            (definition && definition.mangled_name || self.name.name) !==
            self.foreign_name.name;
        if (names_are_different) {
            if (is_import) {
                output.print(self.foreign_name.name);
            } else {
                self.name.print(output);
            }
            output.space();
            output.print("as");
            output.space();
            if (is_import) {
                self.name.print(output);
            } else {
                output.print(self.foreign_name.name);
            }
        } else {
            self.name.print(output);
        }
    });

    DEFPRINT(AST_Export, function(self, output) {
        output.print("export");
        output.space();
        if (self.is_default) {
            output.print("default");
            output.space();
        }
        if (self.exported_names) {
            if (self.exported_names.length === 1 && self.exported_names[0].name.name === "*") {
                self.exported_names[0].print(output);
            } else {
                output.print("{");
                self.exported_names.forEach(function(name_export, i) {
                    output.space();
                    name_export.print(output);
                    if (i < self.exported_names.length - 1) {
                        output.print(",");
                    }
                });
                output.space();
                output.print("}");
            }
        }
        else if (self.exported_value) {
            self.exported_value.print(output);
        } else if (self.exported_definition) {
            self.exported_definition.print(output);
            if (self.exported_definition instanceof AST_Definitions) return;
        }
        if (self.module_name) {
            output.space();
            output.print("from");
            output.space();
            self.module_name.print(output);
        }
        output.semicolon();
    });

    function parenthesize_for_noin(node, output, noin) {
        var parens = false;
        // need to take some precautions here:
        //    https://github.com/mishoo/UglifyJS2/issues/60
        if (noin) node.walk(new TreeWalker(function(node) {
            if (parens || node instanceof AST_Scope) return true;
            if (node instanceof AST_Binary && node.operator == "in") {
                parens = true;
                return true;
            }
        }));
        node.print(output, parens);
    };

    DEFPRINT(AST_VarDef, function(self, output){
        self.name.print(output);
        if (self.value) {
            output.space();
            output.print("=");
            output.space();
            var p = output.parent(1);
            var noin = p instanceof AST_For || p instanceof AST_ForIn;
            parenthesize_for_noin(self.value, output, noin);
        }
    });

    /* -----[ other expressions ]----- */
    DEFPRINT(AST_Call, function(self, output){
        self.expression.print(output);
        if (self instanceof AST_New && !need_constructor_parens(self, output))
            return;
        if (self.expression instanceof AST_Call || self.expression instanceof AST_Lambda) {
            output.add_mapping(self.start);
        }
        output.with_parens(function(){
            self.args.forEach(function(expr, i){
                if (i) output.comma();
                expr.print(output);
            });
        });
    });
    DEFPRINT(AST_New, function(self, output){
        output.print("new");
        output.space();
        AST_Call.prototype._codegen(self, output);
    });

    AST_Sequence.DEFMETHOD("_do_print", function(output){
        this.expressions.forEach(function(node, index) {
            if (index > 0) {
                output.comma();
                if (output.should_break()) {
                    output.newline();
                    output.indent();
                }
            }
            node.print(output);
        });
    });
    DEFPRINT(AST_Sequence, function(self, output){
        self._do_print(output);
        // var p = output.parent();
        // if (p instanceof AST_Statement) {
        //     output.with_indent(output.next_indent(), function(){
        //         self._do_print(output);
        //     });
        // } else {
        //     self._do_print(output);
        // }
    });
    DEFPRINT(AST_Dot, function(self, output){
        var expr = self.expression;
        expr.print(output);
        var prop = self.property;
        if (output.option("ie8") && RESERVED_WORDS(prop)) {
            output.print("[");
            output.add_mapping(self.end);
            output.print_string(prop);
            output.print("]");
        } else {
            if (expr instanceof AST_Number && expr.getValue() >= 0) {
                if (!/[xa-f.)]/i.test(output.last())) {
                    output.print(".");
                }
            }
            output.print(".");
            // the name after dot would be mapped about here.
            output.add_mapping(self.end);
            output.print_name(prop);
        }
    });
    DEFPRINT(AST_Sub, function(self, output){
        self.expression.print(output);
        output.print("[");
        self.property.print(output);
        output.print("]");
    });
    DEFPRINT(AST_UnaryPrefix, function(self, output){
        var op = self.operator;
        output.print(op);
        if (/^[a-z]/i.test(op)
            || (/[+-]$/.test(op)
                && self.expression instanceof AST_UnaryPrefix
                && /^[+-]/.test(self.expression.operator))) {
            output.space();
        }
        self.expression.print(output);
    });
    DEFPRINT(AST_UnaryPostfix, function(self, output){
        self.expression.print(output);
        output.print(self.operator);
    });
    DEFPRINT(AST_Binary, function(self, output){
        var op = self.operator;
        self.left.print(output);
        if (op[0] == ">" /* ">>" ">>>" ">" ">=" */
            && self.left instanceof AST_UnaryPostfix
            && self.left.operator == "--") {
            // space is mandatory to avoid outputting -->
            output.print(" ");
        } else {
            // the space is optional depending on "beautify"
            output.space();
        }
        output.print(op);
        if ((op == "<" || op == "<<")
            && self.right instanceof AST_UnaryPrefix
            && self.right.operator == "!"
            && self.right.expression instanceof AST_UnaryPrefix
            && self.right.expression.operator == "--") {
            // space is mandatory to avoid outputting <!--
            output.print(" ");
        } else {
            // the space is optional depending on "beautify"
            output.space();
        }
        self.right.print(output);
    });
    DEFPRINT(AST_Conditional, function(self, output){
        self.condition.print(output);
        output.space();
        output.print("?");
        output.space();
        self.consequent.print(output);
        output.space();
        output.colon();
        self.alternative.print(output);
    });

    /* -----[ literals ]----- */
    DEFPRINT(AST_Array, function(self, output){
        output.with_square(function(){
            var a = self.elements, len = a.length;
            if (len > 0) output.space();
            a.forEach(function(exp, i){
                if (i) output.comma();
                exp.print(output);
                // If the final element is a hole, we need to make sure it
                // doesn't look like a trailing comma, by inserting an actual
                // trailing comma.
                if (i === len - 1 && exp instanceof AST_Hole)
                  output.comma();
            });
            if (len > 0) output.space();
        });
    });
    DEFPRINT(AST_Object, function(self, output){
        if (self.properties.length > 0) output.with_block(function(){
            self.properties.forEach(function(prop, i){
                if (i) {
                    output.print(",");
                    output.newline();
                }
                output.indent();
                prop.print(output);
            });
            output.newline();
        });
        else output.print("{}");
    });
    DEFPRINT(AST_Class, function(self, output){
        output.print("class");
        output.space();
        if (self.name) {
            self.name.print(output);
            output.space();
        }
        if (self.extends) {
            var parens = (
                   !(self.extends instanceof AST_SymbolRef)
                && !(self.extends instanceof AST_PropAccess)
                && !(self.extends instanceof AST_ClassExpression)
                && !(self.extends instanceof AST_Function)
            );
            output.print("extends");
            if (parens) {
                output.print("(");
            } else {
                output.space();
            }
            self.extends.print(output);
            if (parens) {
                output.print(")");
            } else {
                output.space();
            }
        }
        if (self.properties.length > 0) output.with_block(function(){
            self.properties.forEach(function(prop, i){
                if (i) {
                    output.newline();
                }
                output.indent();
                prop.print(output);
            });
            output.newline();
        });
        else output.print("{}");
    });
    DEFPRINT(AST_NewTarget, function(self, output) {
        output.print("new.target");
    });

    function print_property_name(key, quote, output) {
        if (output.option("quote_keys")) {
            output.print_string(key);
        } else if ("" + +key == key && key >= 0) {
            output.print(make_num(key));
        } else if (RESERVED_WORDS(key) ? !output.option("ie8") : is_identifier_string(key)) {
            if (quote && output.option("keep_quoted_props")) {
                output.print_string(key, quote);
            } else {
                output.print_name(key);
            }
        } else {
            output.print_string(key, quote);
        }
    }

    DEFPRINT(AST_ObjectKeyVal, function(self, output){
        function get_name(self) {
            var def = self.definition();
            return def ? def.mangled_name || def.name : self.name;
        }

        var allowShortHand = output.option("shorthand");
        if (allowShortHand &&
            self.value instanceof AST_Symbol &&
            is_identifier_string(self.key) &&
            get_name(self.value) === self.key &&
            is_identifier(self.key)
        ) {
            print_property_name(self.key, self.quote, output);

        } else if (allowShortHand &&
            self.value instanceof AST_DefaultAssign &&
            self.value.left instanceof AST_Symbol &&
            is_identifier_string(self.key) &&
            get_name(self.value.left) === self.key
        ) {
            print_property_name(self.key, self.quote, output);
            output.space();
            output.print("=");
            output.space();
            self.value.right.print(output);
        } else {
            if (!(self.key instanceof AST_Node)) {
                print_property_name(self.key, self.quote, output);
            } else {
                output.with_square(function() {
                    self.key.print(output);
                });
            }
            output.colon();
            self.value.print(output);
        }
    });
    AST_ObjectProperty.DEFMETHOD("_print_getter_setter", function(type, output) {
        var self = this;
        if (self.static) {
            output.print("static");
            output.space();
        }
        if (type) {
            output.print(type);
            output.space();
        }
        if (self.key instanceof AST_SymbolMethod) {
            print_property_name(self.key.name, self.quote, output);
        } else {
            output.with_square(function() {
                self.key.print(output);
            });
        }
        self.value._do_print(output, true);
    });
    DEFPRINT(AST_ObjectSetter, function(self, output){
        self._print_getter_setter("set", output);
    });
    DEFPRINT(AST_ObjectGetter, function(self, output){
        self._print_getter_setter("get", output);
    });
    DEFPRINT(AST_ConciseMethod, function(self, output){
        self._print_getter_setter(self.is_generator && "*" || self.async && "async", output);
    });
    AST_Symbol.DEFMETHOD("_do_print", function(output){
        var def = this.definition();
        output.print_name(def ? def.mangled_name || def.name : this.name);
    });
    DEFPRINT(AST_Symbol, function (self, output) {
        self._do_print(output);
    });
    DEFPRINT(AST_Hole, noop);
    DEFPRINT(AST_This, function(self, output){
        output.print("this");
    });
    DEFPRINT(AST_Super, function(self, output){
        output.print("super");
    });
    DEFPRINT(AST_Constant, function(self, output){
        output.print(self.getValue());
    });
    DEFPRINT(AST_String, function(self, output){
        output.print_string(self.getValue(), self.quote, in_directive);
    });
    DEFPRINT(AST_Number, function(self, output){
        if (use_asm && self.start && self.start.raw != null) {
            output.print(self.start.raw);
        } else {
            output.print(make_num(self.getValue()));
        }
    });

    DEFPRINT(AST_RegExp, function(self, output){
        var regexp = self.getValue();
        var str = regexp.toString();
        if (regexp.raw_source) {
            str = "/" + regexp.raw_source + str.slice(str.lastIndexOf("/"));
        }
        str = output.to_utf8(str);
        output.print(str);
        var p = output.parent();
        if (p instanceof AST_Binary && /^in/.test(p.operator) && p.left === self)
            output.print(" ");
    });

    function force_statement(stat, output) {
        if (output.option("bracketize")) {
            make_block(stat, output);
        } else {
            if (!stat || stat instanceof AST_EmptyStatement)
                output.force_semicolon();
            else
                stat.print(output);
        }
    };

    // self should be AST_New.  decide if we want to show parens or not.
    function need_constructor_parens(self, output) {
        // Always print parentheses with arguments
        if (self.args.length > 0) return true;

        return output.option("beautify");
    };

    function best_of(a) {
        var best = a[0], len = best.length;
        for (var i = 1; i < a.length; ++i) {
            if (a[i].length < len) {
                best = a[i];
                len = best.length;
            }
        }
        return best;
    };

    function make_num(num) {
        var str = num.toString(10), a = [ str.replace(/^0\./, ".").replace('e+', 'e') ], m;
        if (Math.floor(num) === num) {
            if (num >= 0) {
                a.push("0x" + num.toString(16).toLowerCase(), // probably pointless
                       "0" + num.toString(8)); // same.
            } else {
                a.push("-0x" + (-num).toString(16).toLowerCase(), // probably pointless
                       "-0" + (-num).toString(8)); // same.
            }
            if ((m = /^(.*?)(0+)$/.exec(num))) {
                a.push(m[1] + "e" + m[2].length);
            }
        } else if ((m = /^0?\.(0+)(.*)$/.exec(num))) {
            a.push(m[2] + "e-" + (m[1].length + m[2].length),
                   str.substr(str.indexOf(".")));
        }
        return best_of(a);
    };

    function make_block(stmt, output) {
        if (!stmt || stmt instanceof AST_EmptyStatement)
            output.print("{}");
        else if (stmt instanceof AST_BlockStatement)
            stmt.print(output);
        else output.with_block(function(){
            output.indent();
            stmt.print(output);
            output.newline();
        });
    };

    /* -----[ source map generators ]----- */

    function DEFMAP(nodetype, generator) {
        nodetype.DEFMETHOD("add_source_map", function(stream){
            generator(this, stream);
        });
    };

    // We could easily add info for ALL nodes, but it seems to me that
    // would be quite wasteful, hence this noop in the base class.
    DEFMAP(AST_Node, noop);

    function basic_sourcemap_gen(self, output) {
        output.add_mapping(self.start);
    };

    // XXX: I'm not exactly sure if we need it for all of these nodes,
    // or if we should add even more.

    DEFMAP(AST_Directive, basic_sourcemap_gen);
    DEFMAP(AST_Debugger, basic_sourcemap_gen);
    DEFMAP(AST_Symbol, basic_sourcemap_gen);
    DEFMAP(AST_Jump, basic_sourcemap_gen);
    DEFMAP(AST_StatementWithBody, basic_sourcemap_gen);
    DEFMAP(AST_LabeledStatement, noop); // since the label symbol will mark it
    DEFMAP(AST_Lambda, basic_sourcemap_gen);
    DEFMAP(AST_Switch, basic_sourcemap_gen);
    DEFMAP(AST_SwitchBranch, basic_sourcemap_gen);
    DEFMAP(AST_BlockStatement, basic_sourcemap_gen);
    DEFMAP(AST_Toplevel, noop);
    DEFMAP(AST_New, basic_sourcemap_gen);
    DEFMAP(AST_Try, basic_sourcemap_gen);
    DEFMAP(AST_Catch, basic_sourcemap_gen);
    DEFMAP(AST_Finally, basic_sourcemap_gen);
    DEFMAP(AST_Definitions, basic_sourcemap_gen);
    DEFMAP(AST_Constant, basic_sourcemap_gen);
    DEFMAP(AST_ObjectSetter, function(self, output){
        output.add_mapping(self.start, self.key.name);
    });
    DEFMAP(AST_ObjectGetter, function(self, output){
        output.add_mapping(self.start, self.key.name);
    });
    DEFMAP(AST_ObjectProperty, function(self, output){
        output.add_mapping(self.start, self.key);
    });

})();

/***********************************************************************

  A JavaScript tokenizer / parser / beautifier / compressor.
  https://github.com/mishoo/UglifyJS2

  -------------------------------- (C) ---------------------------------

                           Author: Mihai Bazon
                         <mihai.bazon@gmail.com>
                       http://mihai.bazon.net/blog

  Distributed under the BSD license:

    Copyright 2012 (c) Mihai Bazon <mihai.bazon@gmail.com>

    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions
    are met:

        * Redistributions of source code must retain the above
          copyright notice, this list of conditions and the following
          disclaimer.

        * Redistributions in binary form must reproduce the above
          copyright notice, this list of conditions and the following
          disclaimer in the documentation and/or other materials
          provided with the distribution.

    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER “AS IS” AND ANY
    EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
    IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
    PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER BE
    LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY,
    OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
    PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
    PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
    THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR
    TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
    THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
    SUCH DAMAGE.

 ***********************************************************************/

"use strict";

function Compressor(options, false_by_default) {
    if (!(this instanceof Compressor))
        return new Compressor(options, false_by_default);
    TreeTransformer.call(this, this.before, this.after);
    this.options = defaults(options, {
        arrows        : !false_by_default,
        booleans      : !false_by_default,
        collapse_vars : !false_by_default,
        comparisons   : !false_by_default,
        computed_props: !false_by_default,
        conditionals  : !false_by_default,
        dead_code     : !false_by_default,
        drop_console  : false,
        drop_debugger : !false_by_default,
        ecma          : 5,
        evaluate      : !false_by_default,
        expression    : false,
        global_defs   : {},
        hoist_funs    : false,
        hoist_props   : !false_by_default,
        hoist_vars    : false,
        ie8           : false,
        if_return     : !false_by_default,
        inline        : !false_by_default,
        join_vars     : !false_by_default,
        keep_classnames: false,
        keep_fargs    : true,
        keep_fnames   : false,
        keep_infinity : false,
        loops         : !false_by_default,
        negate_iife   : !false_by_default,
        passes        : 1,
        properties    : !false_by_default,
        pure_getters  : !false_by_default && "strict",
        pure_funcs    : null,
        reduce_funcs  : !false_by_default,
        reduce_vars   : !false_by_default,
        sequences     : !false_by_default,
        side_effects  : !false_by_default,
        switches      : !false_by_default,
        top_retain    : null,
        toplevel      : !!(options && options["top_retain"]),
        typeofs       : !false_by_default,
        unsafe        : false,
        unsafe_arrows : false,
        unsafe_comps  : false,
        unsafe_Function: false,
        unsafe_math   : false,
        unsafe_methods: false,
        unsafe_proto  : false,
        unsafe_regexp : false,
        unsafe_undefined: false,
        unused        : !false_by_default,
        warnings      : false,
    }, true);
    var global_defs = this.options["global_defs"];
    if (typeof global_defs == "object") for (var key in global_defs) {
        if (/^@/.test(key) && HOP(global_defs, key)) {
            global_defs[key.slice(1)] = parse(global_defs[key], {
                expression: true
            });
        }
    }
    if (this.options["inline"] === true) this.options["inline"] = 3;
    var pure_funcs = this.options["pure_funcs"];
    if (typeof pure_funcs == "function") {
        this.pure_funcs = pure_funcs;
    } else {
        this.pure_funcs = pure_funcs ? function(node) {
            return pure_funcs.indexOf(node.expression.print_to_string()) < 0;
        } : return_true;
    }
    var top_retain = this.options["top_retain"];
    if (top_retain instanceof RegExp) {
        this.top_retain = function(def) {
            return top_retain.test(def.name);
        };
    } else if (typeof top_retain == "function") {
        this.top_retain = top_retain;
    } else if (top_retain) {
        if (typeof top_retain == "string") {
            top_retain = top_retain.split(/,/);
        }
        this.top_retain = function(def) {
            return top_retain.indexOf(def.name) >= 0;
        };
    }
    var toplevel = this.options["toplevel"];
    this.toplevel = typeof toplevel == "string" ? {
        funcs: /funcs/.test(toplevel),
        vars: /vars/.test(toplevel)
    } : {
        funcs: toplevel,
        vars: toplevel
    };
    var sequences = this.options["sequences"];
    this.sequences_limit = sequences == 1 ? 800 : sequences | 0;
    this.warnings_produced = {};
};

Compressor.prototype = new TreeTransformer;
merge(Compressor.prototype, {
    option: function(key) { return this.options[key] },
    exposed: function(def) {
        if (def.export) return true;
        if (def.global) for (var i = 0, len = def.orig.length; i < len; i++)
            if (!this.toplevel[def.orig[i] instanceof AST_SymbolDefun ? "funcs" : "vars"])
                return true;
        return false;
    },
    in_boolean_context: function() {
        if (!this.option("booleans")) return false;
        var self = this.self();
        for (var i = 0, p; p = this.parent(i); i++) {
            if (p instanceof AST_SimpleStatement
                || p instanceof AST_Conditional && p.condition === self
                || p instanceof AST_DWLoop && p.condition === self
                || p instanceof AST_For && p.condition === self
                || p instanceof AST_If && p.condition === self
                || p instanceof AST_UnaryPrefix && p.operator == "!" && p.expression === self) {
                return true;
            }
            if (p instanceof AST_Binary && (p.operator == "&&" || p.operator == "||")
                || p instanceof AST_Conditional
                || p.tail_node() === self) {
                self = p;
            } else {
                return false;
            }
        }
    },
    compress: function(node) {
        if (this.option("expression")) {
            node.process_expression(true);
        }
        var passes = +this.options.passes || 1;
        var min_count = 1 / 0;
        var stopping = false;
        var mangle = { ie8: this.option("ie8") };
        for (var pass = 0; pass < passes; pass++) {
            node.figure_out_scope(mangle);
            if (pass > 0 || this.option("reduce_vars"))
                node.reset_opt_flags(this);
            node = node.transform(this);
            if (passes > 1) {
                var count = 0;
                node.walk(new TreeWalker(function() {
                    count++;
                }));
                this.info("pass " + pass + ": last_count: " + min_count + ", count: " + count);
                if (count < min_count) {
                    min_count = count;
                    stopping = false;
                } else if (stopping) {
                    break;
                } else {
                    stopping = true;
                }
            }
        }
        if (this.option("expression")) {
            node.process_expression(false);
        }
        return node;
    },
    info: function() {
        if (this.options.warnings == "verbose") {
            AST_Node.warn.apply(AST_Node, arguments);
        }
    },
    warn: function(text, props) {
        if (this.options.warnings) {
            // only emit unique warnings
            var message = string_template(text, props);
            if (!(message in this.warnings_produced)) {
                this.warnings_produced[message] = true;
                AST_Node.warn.apply(AST_Node, arguments);
            }
        }
    },
    clear_warnings: function() {
        this.warnings_produced = {};
    },
    before: function(node, descend, in_list) {
        if (node._squeezed) return node;
        var was_scope = false;
        if (node instanceof AST_Scope) {
            node = node.hoist_properties(this);
            node = node.hoist_declarations(this);
            was_scope = true;
        }
        // Before https://github.com/mishoo/UglifyJS2/pull/1602 AST_Node.optimize()
        // would call AST_Node.transform() if a different instance of AST_Node is
        // produced after OPT().
        // This corrupts TreeWalker.stack, which cause AST look-ups to malfunction.
        // Migrate and defer all children's AST_Node.transform() to below, which
        // will now happen after this parent AST_Node has been properly substituted
        // thus gives a consistent AST snapshot.
        descend(node, this);
        // Existing code relies on how AST_Node.optimize() worked, and omitting the
        // following replacement call would result in degraded efficiency of both
        // output and performance.
        descend(node, this);
        var opt = node.optimize(this);
        if (was_scope && opt instanceof AST_Scope) {
            opt.drop_unused(this);
            descend(opt, this);
        }
        if (opt === node) opt._squeezed = true;
        return opt;
    }
});

(function(){

    function OPT(node, optimizer) {
        node.DEFMETHOD("optimize", function(compressor){
            var self = this;
            if (self._optimized) return self;
            if (compressor.has_directive("use asm")) return self;
            var opt = optimizer(self, compressor);
            opt._optimized = true;
            return opt;
        });
    };

    OPT(AST_Node, function(self, compressor){
        return self;
    });

    AST_Node.DEFMETHOD("equivalent_to", function(node){
        return this.TYPE == node.TYPE && this.print_to_string() == node.print_to_string();
    });

    AST_Scope.DEFMETHOD("process_expression", function(insert, compressor) {
        var self = this;
        var tt = new TreeTransformer(function(node) {
            if (insert && node instanceof AST_SimpleStatement) {
                return make_node(AST_Return, node, {
                    value: node.body
                });
            }
            if (!insert && node instanceof AST_Return) {
                if (compressor) {
                    var value = node.value && node.value.drop_side_effect_free(compressor, true);
                    return value ? make_node(AST_SimpleStatement, node, {
                        body: value
                    }) : make_node(AST_EmptyStatement, node);
                }
                return make_node(AST_SimpleStatement, node, {
                    body: node.value || make_node(AST_UnaryPrefix, node, {
                        operator: "void",
                        expression: make_node(AST_Number, node, {
                            value: 0
                        })
                    })
                });
            }
            if (node instanceof AST_Class || node instanceof AST_Lambda && node !== self) {
                return node;
            }
            if (node instanceof AST_Block) {
                var index = node.body.length - 1;
                if (index >= 0) {
                    node.body[index] = node.body[index].transform(tt);
                }
            } else if (node instanceof AST_If) {
                node.body = node.body.transform(tt);
                if (node.alternative) {
                    node.alternative = node.alternative.transform(tt);
                }
            } else if (node instanceof AST_With) {
                node.body = node.body.transform(tt);
            }
            return node;
        });
        self.transform(tt);
    });

    (function(def){
        def(AST_Node, noop);

        function reset_def(compressor, def) {
            def.assignments = 0;
            def.chained = false;
            def.direct_access = false;
            def.escaped = false;
            if (def.scope.uses_eval || def.scope.uses_with) {
                def.fixed = false;
            } else if (def.orig[0] instanceof AST_SymbolConst || !compressor.exposed(def)) {
                def.fixed = def.init;
            } else {
                def.fixed = false;
            }
            def.recursive_refs = 0;
            def.references = [];
            def.should_replace = undefined;
            def.single_use = undefined;
        }

        function reset_variables(tw, compressor, node) {
            node.variables.each(function(def) {
                reset_def(compressor, def);
                if (def.fixed === null) {
                    def.safe_ids = tw.safe_ids;
                    mark(tw, def, true);
                } else if (def.fixed) {
                    tw.loop_ids[def.id] = tw.in_loop;
                    mark(tw, def, true);
                }
            });
        }

        function reset_block_variables(compressor, node) {
            if (node.block_scope) node.block_scope.variables.each(function(def) {
                reset_def(compressor, def);
            });
        }

        function push(tw) {
            tw.safe_ids = Object.create(tw.safe_ids);
        }

        function pop(tw) {
            tw.safe_ids = Object.getPrototypeOf(tw.safe_ids);
        }

        function mark(tw, def, safe) {
            tw.safe_ids[def.id] = safe;
        }

        function safe_to_read(tw, def) {
            if (tw.safe_ids[def.id]) {
                if (def.fixed == null) {
                    var orig = def.orig[0];
                    if (orig instanceof AST_SymbolFunarg || orig.name == "arguments") return false;
                    def.fixed = make_node(AST_Undefined, orig);
                }
                return true;
            }
            return def.fixed instanceof AST_Defun;
        }

        function safe_to_assign(tw, def, value) {
            if (def.fixed === undefined) return true;
            if (def.fixed === null && def.safe_ids) {
                def.safe_ids[def.id] = false;
                delete def.safe_ids;
                return true;
            }
            if (!HOP(tw.safe_ids, def.id)) return false;
            if (!safe_to_read(tw, def)) return false;
            if (def.fixed === false) return false;
            if (def.fixed != null && (!value || def.references.length > def.assignments)) return false;
            return all(def.orig, function(sym) {
                return !(sym instanceof AST_SymbolConst
                    || sym instanceof AST_SymbolDefun
                    || sym instanceof AST_SymbolLambda);
            });
        }

        function ref_once(tw, compressor, def) {
            return compressor.option("unused")
                && !def.scope.uses_eval
                && !def.scope.uses_with
                && def.references.length - def.recursive_refs == 1
                && tw.loop_ids[def.id] === tw.in_loop;
        }

        function is_immutable(value) {
            if (!value) return false;
            return value.is_constant()
                || value instanceof AST_Lambda
                || value instanceof AST_This;
        }

        function read_property(obj, key) {
            key = get_value(key);
            if (key instanceof AST_Node) return;
            var value;
            if (obj instanceof AST_Array) {
                var elements = obj.elements;
                if (key == "length") return make_node_from_constant(elements.length, obj);
                if (typeof key == "number" && key in elements) value = elements[key];
            } else if (obj instanceof AST_Object) {
                key = "" + key;
                var props = obj.properties;
                for (var i = props.length; --i >= 0;) {
                    var prop = props[i];
                    if (!(prop instanceof AST_ObjectKeyVal)) return;
                    if (!value && props[i].key === key) value = props[i].value;
                }
            }
            return value instanceof AST_SymbolRef && value.fixed_value() || value;
        }

        function is_modified(tw, node, value, level, immutable) {
            var parent = tw.parent(level);
            if (is_lhs(node, parent)
                || !immutable
                    && parent instanceof AST_Call
                    && parent.expression === node
                    && !(value instanceof AST_Arrow)
                    && !(value instanceof AST_Class)
                    && (!(value instanceof AST_Function)
                        || !(parent instanceof AST_New) && value.contains_this())) {
                return true;
            } else if (parent instanceof AST_Array) {
                return is_modified(tw, parent, parent, level + 1);
            } else if (parent instanceof AST_ObjectKeyVal && node === parent.value) {
                var obj = tw.parent(level + 1);
                return is_modified(tw, obj, obj, level + 2);
            } else if (parent instanceof AST_PropAccess && parent.expression === node) {
                return !immutable && is_modified(tw, parent, read_property(value, parent.property), level + 1);
            }
        }

        function mark_escaped(tw, d, scope, node, value, level, depth) {
            var parent = tw.parent(level);
            if (value) {
                if (value.is_constant()) return;
                if (value instanceof AST_ClassExpression) return;
            }
            if (parent instanceof AST_Assign && parent.operator == "=" && node === parent.right
                || parent instanceof AST_Call && node !== parent.expression
                || parent instanceof AST_Exit && node === parent.value && node.scope !== d.scope
                || parent instanceof AST_VarDef && node === parent.value
                || parent instanceof AST_Yield && node === parent.value && node.scope !== d.scope) {
                if (depth > 1 && !(value && value.is_constant_expression(scope))) depth = 1;
                if (!d.escaped || d.escaped > depth) d.escaped = depth;
                return;
            } else if (parent instanceof AST_Array
                || parent instanceof AST_Await
                || parent instanceof AST_Binary && lazy_op(parent.operator)
                || parent instanceof AST_Conditional && node !== parent.condition
                || parent instanceof AST_Expansion
                || parent instanceof AST_Sequence && node === parent.tail_node()) {
                mark_escaped(tw, d, scope, parent, parent, level + 1, depth);
            } else if (parent instanceof AST_ObjectKeyVal && node === parent.value) {
                var obj = tw.parent(level + 1);
                mark_escaped(tw, d, scope, obj, obj, level + 2, depth);
            } else if (parent instanceof AST_PropAccess && node === parent.expression) {
                value = read_property(value, parent.property);
                mark_escaped(tw, d, scope, parent, value, level + 1, depth + 1);
                if (value) return;
            }
            if (level == 0) d.direct_access = true;
        }

        var suppressor = new TreeWalker(function(node) {
            if (!(node instanceof AST_Symbol)) return;
            var d = node.definition();
            if (!d) return;
            if (node instanceof AST_SymbolRef) d.references.push(node);
            d.fixed = false;
        });
        def(AST_Accessor, function(tw, descend, compressor) {
            push(tw);
            reset_variables(tw, compressor, this);
            descend();
            pop(tw);
            return true;
        });
        def(AST_Arrow, mark_func_expr);
        def(AST_Assign, function(tw) {
            var node = this;
            if (node.left instanceof AST_Destructuring) {
                node.left.walk(suppressor);
                return;
            }
            if (!(node.left instanceof AST_SymbolRef)) return;
            var d = node.left.definition();
            var fixed = d.fixed;
            if (!fixed && node.operator != "=") return;
            if (!safe_to_assign(tw, d, node.right)) return;
            d.references.push(node.left);
            d.assignments++;
            if (node.operator != "=") d.chained = true;
            d.fixed = node.operator == "=" ? function() {
                return node.right;
            } : function() {
                return make_node(AST_Binary, node, {
                    operator: node.operator.slice(0, -1),
                    left: fixed instanceof AST_Node ? fixed : fixed(),
                    right: node.right
                });
            };
            mark(tw, d, false);
            node.right.walk(tw);
            mark(tw, d, true);
            return true;
        });
        def(AST_Binary, function(tw) {
            if (!lazy_op(this.operator)) return;
            this.left.walk(tw);
            push(tw);
            this.right.walk(tw);
            pop(tw);
            return true;
        });
        def(AST_Block, function(tw, descend, compressor) {
            reset_block_variables(compressor, this);
        });
        def(AST_ClassExpression, function(tw, descend) {
            this.inlined = false;
            push(tw);
            descend();
            pop(tw);
            return true;
        })
        def(AST_Conditional, function(tw) {
            this.condition.walk(tw);
            push(tw);
            this.consequent.walk(tw);
            pop(tw);
            push(tw);
            this.alternative.walk(tw);
            pop(tw);
            return true;
        });

        function mark_def_node(tw, descend, compressor) {
            this.inlined = false;
            var save_ids = tw.safe_ids;
            tw.safe_ids = Object.create(null);
            reset_variables(tw, compressor, this);
            descend();
            tw.safe_ids = save_ids;
            return true;
        }

        def(AST_DefClass, mark_def_node);
        def(AST_Defun, mark_def_node);
        def(AST_Do, function(tw, descend, compressor) {
            reset_block_variables(compressor, this);
            var saved_loop = tw.in_loop;
            tw.in_loop = this;
            push(tw);
            this.body.walk(tw);
            this.condition.walk(tw);
            pop(tw);
            tw.in_loop = saved_loop;
            return true;
        });
        def(AST_For, function(tw, descend, compressor) {
            reset_block_variables(compressor, this);
            if (this.init) this.init.walk(tw);
            var saved_loop = tw.in_loop;
            tw.in_loop = this;
            if (this.condition) {
                push(tw);
                this.condition.walk(tw);
                pop(tw);
            }
            push(tw);
            this.body.walk(tw);
            pop(tw);
            if (this.step) {
                push(tw);
                this.step.walk(tw);
                pop(tw);
            }
            tw.in_loop = saved_loop;
            return true;
        });
        def(AST_ForIn, function(tw, descend, compressor) {
            reset_block_variables(compressor, this);
            this.init.walk(suppressor);
            this.object.walk(tw);
            var saved_loop = tw.in_loop;
            tw.in_loop = this;
            push(tw);
            this.body.walk(tw);
            pop(tw);
            tw.in_loop = saved_loop;
            return true;
        });

        function mark_func_expr(tw, descend, compressor) {
            var node = this;
            node.inlined = false;
            push(tw);
            reset_variables(tw, compressor, node);
            var iife;
            if (!node.name
                && (iife = tw.parent()) instanceof AST_Call
                && iife.expression === node) {
                // Virtually turn IIFE parameters into variable definitions:
                //   (function(a,b) {...})(c,d) => (function() {var a=c,b=d; ...})()
                // So existing transformation rules can work on them.
                node.argnames.forEach(function(arg, i) {
                    if (!arg.definition) return;
                    var d = arg.definition();
                    if (!node.uses_arguments && d.fixed === undefined) {
                        d.fixed = function() {
                            return iife.args[i] || make_node(AST_Undefined, iife);
                        };
                        tw.loop_ids[d.id] = tw.in_loop;
                        mark(tw, d, true);
                    } else {
                        d.fixed = false;
                    }
                });
            }
            descend();
            pop(tw);
            return true;
        }

        def(AST_Function, mark_func_expr);
        def(AST_If, function(tw) {
            this.condition.walk(tw);
            push(tw);
            this.body.walk(tw);
            pop(tw);
            if (this.alternative) {
                push(tw);
                this.alternative.walk(tw);
                pop(tw);
            }
            return true;
        });
        def(AST_LabeledStatement, function(tw) {
            push(tw);
            this.body.walk(tw);
            pop(tw);
            return true;
        });
        def(AST_SwitchBranch, function(tw, descend) {
            push(tw);
            descend();
            pop(tw);
            return true;
        });
        def(AST_SymbolCatch, function() {
            this.definition().fixed = false;
        });
        def(AST_SymbolRef, function(tw, descend, compressor) {
            var d = this.definition();
            d.references.push(this);
            if (d.references.length == 1
                && !d.fixed
                && d.orig[0] instanceof AST_SymbolDefun) {
                tw.loop_ids[d.id] = tw.in_loop;
            }
            var value;
            if (d.fixed === undefined || !safe_to_read(tw, d) || d.single_use == "m") {
                d.fixed = false;
            } else if (d.fixed) {
                value = this.fixed_value();
                if (value instanceof AST_Lambda && recursive_ref(tw, d)) {
                    d.recursive_refs++;
                } else if (value && !compressor.exposed(d) && ref_once(tw, compressor, d)) {
                    d.single_use = value instanceof AST_Lambda
                        || value instanceof AST_Class
                        || d.scope === this.scope && value.is_constant_expression();
                } else {
                    d.single_use = false;
                }
                if (is_modified(tw, this, value, 0, is_immutable(value))) {
                    if (d.single_use) {
                        d.single_use = "m";
                    } else {
                        d.fixed = false;
                    }
                }
            }
            mark_escaped(tw, d, this.scope, this, value, 0, 1);
        });
        def(AST_Toplevel, function(tw, descend, compressor) {
            this.globals.each(function(def) {
                reset_def(compressor, def);
            });
            reset_variables(tw, compressor, this);
        });
        def(AST_Try, function(tw, descend, compressor) {
            reset_block_variables(compressor, this);
            push(tw);
            walk_body(this, tw);
            pop(tw);
            if (this.bcatch) {
                push(tw);
                this.bcatch.walk(tw);
                pop(tw);
            }
            if (this.bfinally) this.bfinally.walk(tw);
            return true;
        });
        def(AST_Unary, function(tw, descend) {
            var node = this;
            if (node.operator != "++" && node.operator != "--") return;
            if (!(node.expression instanceof AST_SymbolRef)) return;
            var d = node.expression.definition();
            var fixed = d.fixed;
            if (!fixed) return;
            if (!safe_to_assign(tw, d, true)) return;
            d.references.push(node.expression);
            d.assignments++;
            d.chained = true;
            d.fixed = function() {
                return make_node(AST_Binary, node, {
                    operator: node.operator.slice(0, -1),
                    left: make_node(AST_UnaryPrefix, node, {
                        operator: "+",
                        expression: fixed instanceof AST_Node ? fixed : fixed()
                    }),
                    right: make_node(AST_Number, node, {
                        value: 1
                    })
                });
            };
            mark(tw, d, true);
            return true;
        });
        def(AST_VarDef, function(tw, descend) {
            var node = this;
            if (node.name instanceof AST_Destructuring) {
                node.name.walk(suppressor);
                return;
            }
            var d = node.name.definition();
            if (node.value) {
                if (safe_to_assign(tw, d, node.value)) {
                    d.fixed = function() {
                        return node.value;
                    };
                    tw.loop_ids[d.id] = tw.in_loop;
                    mark(tw, d, false);
                    descend();
                    mark(tw, d, true);
                    return true;
                } else {
                    d.fixed = false;
                }
            }
        });
        def(AST_While, function(tw, descend, compressor) {
            reset_block_variables(compressor, this);
            var saved_loop = tw.in_loop;
            tw.in_loop = this;
            push(tw);
            this.condition.walk(tw);
            this.body.walk(tw);
            pop(tw);
            tw.in_loop = saved_loop;
            return true;
        });
    })(function(node, func){
        node.DEFMETHOD("reduce_vars", func);
    });

    AST_Toplevel.DEFMETHOD("reset_opt_flags", function(compressor) {
        var reduce_vars = compressor.option("reduce_vars");
        var tw = new TreeWalker(function(node, descend) {
            node._squeezed = false;
            node._optimized = false;
            if (reduce_vars) return node.reduce_vars(tw, descend, compressor);
        });
        // Stack of look-up tables to keep track of whether a `SymbolDef` has been
        // properly assigned before use:
        // - `push()` & `pop()` when visiting conditional branches
        // - backup & restore via `save_ids` when visiting out-of-order sections
        tw.safe_ids = Object.create(null);
        tw.in_loop = null;
        tw.loop_ids = Object.create(null);
        this.walk(tw);
    });

    AST_Symbol.DEFMETHOD("fixed_value", function() {
        var fixed = this.definition().fixed;
        if (!fixed || fixed instanceof AST_Node) return fixed;
        return fixed();
    });

    AST_SymbolRef.DEFMETHOD("is_immutable", function() {
        var orig = this.definition().orig;
        return orig.length == 1 && orig[0] instanceof AST_SymbolLambda;
    });

    function is_func_expr(node) {
        return node instanceof AST_Arrow || node instanceof AST_Function;
    }

    function is_lhs_read_only(lhs) {
        if (lhs instanceof AST_This) return true;
        if (lhs instanceof AST_SymbolRef) return lhs.definition().orig[0] instanceof AST_SymbolLambda;
        if (lhs instanceof AST_PropAccess) {
            lhs = lhs.expression;
            if (lhs instanceof AST_SymbolRef) {
                if (lhs.is_immutable()) return false;
                lhs = lhs.fixed_value();
            }
            if (!lhs) return true;
            if (lhs instanceof AST_RegExp) return false;
            if (lhs instanceof AST_Constant) return true;
            return is_lhs_read_only(lhs);
        }
        return false;
    }

    function is_ref_of(ref, type) {
        if (!(ref instanceof AST_SymbolRef)) return false;
        var orig = ref.definition().orig;
        for (var i = orig.length; --i >= 0;) {
            if (orig[i] instanceof type) return true;
        }
    }

    function find_variable(compressor, name) {
        var scope, i = 0;
        while (scope = compressor.parent(i++)) {
            if (scope instanceof AST_Scope) break;
            if (scope instanceof AST_Catch) {
                scope = scope.argname.definition().scope;
                break;
            }
        }
        return scope.find_variable(name);
    }

    function make_node(ctor, orig, props) {
        if (!props) props = {};
        if (orig) {
            if (!props.start) props.start = orig.start;
            if (!props.end) props.end = orig.end;
        }
        return new ctor(props);
    };

    function make_sequence(orig, expressions) {
        if (expressions.length == 1) return expressions[0];
        return make_node(AST_Sequence, orig, {
            expressions: expressions.reduce(merge_sequence, [])
        });
    }

    function make_node_from_constant(val, orig) {
        switch (typeof val) {
          case "string":
            return make_node(AST_String, orig, {
                value: val
            });
          case "number":
            if (isNaN(val)) return make_node(AST_NaN, orig);
            if (isFinite(val)) {
                return 1 / val < 0 ? make_node(AST_UnaryPrefix, orig, {
                    operator: "-",
                    expression: make_node(AST_Number, orig, { value: -val })
                }) : make_node(AST_Number, orig, { value: val });
            }
            return val < 0 ? make_node(AST_UnaryPrefix, orig, {
                operator: "-",
                expression: make_node(AST_Infinity, orig)
            }) : make_node(AST_Infinity, orig);
          case "boolean":
            return make_node(val ? AST_True : AST_False, orig);
          case "undefined":
            return make_node(AST_Undefined, orig);
          default:
            if (val === null) {
                return make_node(AST_Null, orig, { value: null });
            }
            if (val instanceof RegExp) {
                return make_node(AST_RegExp, orig, { value: val });
            }
            throw new Error(string_template("Can't handle constant of type: {type}", {
                type: typeof val
            }));
        }
    };

    // we shouldn't compress (1,func)(something) to
    // func(something) because that changes the meaning of
    // the func (becomes lexical instead of global).
    function maintain_this_binding(parent, orig, val) {
        if (parent instanceof AST_UnaryPrefix && parent.operator == "delete"
            || parent instanceof AST_Call && parent.expression === orig
                && (val instanceof AST_PropAccess || val instanceof AST_SymbolRef && val.name == "eval")) {
            return make_sequence(orig, [ make_node(AST_Number, orig, { value: 0 }), val ]);
        }
        return val;
    }

    function merge_sequence(array, node) {
        if (node instanceof AST_Sequence) {
            array.push.apply(array, node.expressions);
        } else {
            array.push(node);
        }
        return array;
    }

    function as_statement_array(thing) {
        if (thing === null) return [];
        if (thing instanceof AST_BlockStatement) return thing.body;
        if (thing instanceof AST_EmptyStatement) return [];
        if (thing instanceof AST_Statement) return [ thing ];
        throw new Error("Can't convert thing to statement array");
    };

    function is_empty(thing) {
        if (thing === null) return true;
        if (thing instanceof AST_EmptyStatement) return true;
        if (thing instanceof AST_BlockStatement) return thing.body.length == 0;
        return false;
    };

    function can_be_evicted_from_block(node) {
        return !(
            node instanceof AST_DefClass ||
            node instanceof AST_Defun ||
            node instanceof AST_Let ||
            node instanceof AST_Const ||
            node instanceof AST_Export ||
            node instanceof AST_Import
        );
    }

    function loop_body(x) {
        if (x instanceof AST_IterationStatement) {
            return x.body instanceof AST_BlockStatement ? x.body : x;
        }
        return x;
    };

    function is_iife_call(node) {
        if (node.TYPE != "Call") return false;
        return node.expression instanceof AST_Function || is_iife_call(node.expression);
    }

    function is_undeclared_ref(node) {
        return node instanceof AST_SymbolRef && node.definition().undeclared;
    }

    var global_names = makePredicate("Array Boolean clearInterval clearTimeout console Date decodeURI decodeURIComponent encodeURI encodeURIComponent Error escape eval EvalError Function isFinite isNaN JSON Math Number parseFloat parseInt RangeError ReferenceError RegExp Object setInterval setTimeout String SyntaxError TypeError unescape URIError");
    AST_SymbolRef.DEFMETHOD("is_declared", function(compressor) {
        return !this.definition().undeclared
            || compressor.option("unsafe") && global_names(this.name);
    });

    var identifier_atom = makePredicate("Infinity NaN undefined");
    function is_identifier_atom(node) {
        return node instanceof AST_Infinity
            || node instanceof AST_NaN
            || node instanceof AST_Undefined;
    }

    function tighten_body(statements, compressor) {
        var scope = compressor.find_parent(AST_Scope).get_defun_scope();
        var CHANGED, max_iter = 10;
        do {
            CHANGED = false;
            eliminate_spurious_blocks(statements);
            if (compressor.option("dead_code")) {
                eliminate_dead_code(statements, compressor);
            }
            if (compressor.option("if_return")) {
                handle_if_return(statements, compressor);
            }
            if (compressor.sequences_limit > 0) {
                sequencesize(statements, compressor);
                sequencesize_2(statements, compressor);
            }
            if (compressor.option("join_vars")) {
                join_consecutive_vars(statements);
            }
            if (compressor.option("collapse_vars")) {
                collapse(statements, compressor);
            }
        } while (CHANGED && max_iter-- > 0);

        // Search from right to left for assignment-like expressions:
        // - `var a = x;`
        // - `a = x;`
        // - `++a`
        // For each candidate, scan from left to right for first usage, then try
        // to fold assignment into the site for compression.
        // Will not attempt to collapse assignments into or past code blocks
        // which are not sequentially executed, e.g. loops and conditionals.
        function collapse(statements, compressor) {
            if (scope.uses_eval || scope.uses_with) return statements;
            var args;
            var candidates = [];
            var in_try = compressor.self() instanceof AST_Try;
            var stat_index = statements.length;
            var scanner = new TreeTransformer(function(node, descend) {
                if (abort) return node;
                // Skip nodes before `candidate` as quickly as possible
                if (!hit) {
                    if (node !== hit_stack[hit_index]) return node;
                    hit_index++;
                    if (hit_index < hit_stack.length) return handle_custom_scan_order(node);
                    hit = true;
                    stop_after = find_stop(node, 0);
                    if (stop_after === node) abort = true;
                    return node;
                }
                // Stop immediately if these node types are encountered
                var parent = scanner.parent();
                if (node instanceof AST_Assign && node.operator != "=" && lhs.equivalent_to(node.left)
                    || node instanceof AST_Await
                    || node instanceof AST_Call && lhs instanceof AST_PropAccess && lhs.equivalent_to(node.expression)
                    || node instanceof AST_Debugger
                    || node instanceof AST_Destructuring
                    || node instanceof AST_IterationStatement && !(node instanceof AST_For)
                    || node instanceof AST_LoopControl
                    || node instanceof AST_Try
                    || node instanceof AST_With
                    || parent instanceof AST_For && node !== parent.init
                    || (side_effects || !replace_all)
                        && (node instanceof AST_SymbolRef && !node.is_declared(compressor))) {
                    abort = true;
                    return node;
                }
                // Stop only if candidate is found within conditional branches
                if (!stop_if_hit && (side_effects || !replace_all)
                    && (parent instanceof AST_Binary && lazy_op(parent.operator) && parent.left !== node
                        || parent instanceof AST_Conditional && parent.condition !== node
                        || parent instanceof AST_If && parent.condition !== node)) {
                    stop_if_hit = parent;
                }
                // Replace variable with assignment when found
                if (can_replace
                    && !(node instanceof AST_SymbolDeclaration)
                    && lhs.equivalent_to(node)) {
                    if (stop_if_hit) {
                        abort = true;
                        return node;
                    }
                    if (is_lhs(node, parent)) {
                        if (value_def) replaced++;
                        return node;
                    }
                    CHANGED = abort = true;
                    replaced++;
                    compressor.info("Collapsing {name} [{file}:{line},{col}]", {
                        name: node.print_to_string(),
                        file: node.start.file,
                        line: node.start.line,
                        col: node.start.col
                    });
                    if (candidate instanceof AST_UnaryPostfix) {
                        return make_node(AST_UnaryPrefix, candidate, candidate);
                    }
                    if (candidate instanceof AST_VarDef) {
                        if (value_def) {
                            abort = false;
                            return node;
                        }
                        var def = candidate.name.definition();
                        var value = candidate.value;
                        if (def.references.length - def.replaced == 1 && !compressor.exposed(def)) {
                            def.replaced++;
                            if (funarg && is_identifier_atom(value)) {
                                return value.transform(compressor);
                            } else {
                                return maintain_this_binding(parent, node, value);
                            }
                        }
                        return make_node(AST_Assign, candidate, {
                            operator: "=",
                            left: make_node(AST_SymbolRef, candidate.name, candidate.name),
                            right: value
                        });
                    }
                    candidate.write_only = false;
                    return candidate;
                }
                // These node types have child nodes that execute sequentially,
                // but are otherwise not safe to scan into or beyond them.
                var sym;
                if (node instanceof AST_Call
                    || node instanceof AST_Exit
                        && (side_effects || lhs instanceof AST_PropAccess || may_modify(lhs))
                    || node instanceof AST_PropAccess
                        && (side_effects || node.expression.may_throw_on_access(compressor))
                    || node instanceof AST_SymbolRef
                        && (lvalues[node.name] || side_effects && may_modify(node))
                    || node instanceof AST_VarDef && node.value
                        && (node.name.name in lvalues || side_effects && may_modify(node.name))
                    || (sym = is_lhs(node.left, node))
                        && (sym instanceof AST_PropAccess || sym.name in lvalues)
                    || may_throw
                        && (in_try ? node.has_side_effects(compressor) : side_effects_external(node))) {
                    stop_after = node;
                    if (node instanceof AST_Scope) abort = true;
                }
                return handle_custom_scan_order(node);
            }, function(node) {
                if (abort) return;
                if (stop_after === node) abort = true;
                if (stop_if_hit === node) stop_if_hit = null;
            });
            var multi_replacer = new TreeTransformer(function(node) {
                if (abort) return node;
                // Skip nodes before `candidate` as quickly as possible
                if (!hit) {
                    if (node !== hit_stack[hit_index]) return node;
                    hit_index++;
                    if (hit_index < hit_stack.length) return;
                    hit = true;
                    return node;
                }
                // Replace variable when found
                if (node instanceof AST_SymbolRef
                    && node.name == def.name) {
                    if (!--replaced) abort = true;
                    if (is_lhs(node, multi_replacer.parent())) return node;
                    def.replaced++;
                    value_def.replaced--;
                    return candidate.value;
                }
                // Skip (non-executed) functions and (leading) default case in switch statements
                if (node instanceof AST_Default || node instanceof AST_Scope) return node;
            });
            while (--stat_index >= 0) {
                // Treat parameters as collapsible in IIFE, i.e.
                //   function(a, b){ ... }(x());
                // would be translated into equivalent assignments:
                //   var a = x(), b = undefined;
                if (stat_index == 0 && compressor.option("unused")) extract_args();
                // Find collapsible assignments
                var hit_stack = [];
                extract_candidates(statements[stat_index]);
                while (candidates.length > 0) {
                    hit_stack = candidates.pop();
                    var hit_index = 0;
                    var candidate = hit_stack[hit_stack.length - 1];
                    var value_def = null;
                    var stop_after = null;
                    var stop_if_hit = null;
                    var lhs = get_lhs(candidate);
                    if (!lhs || is_lhs_read_only(lhs) || lhs.has_side_effects(compressor)) continue;
                    // Locate symbols which may execute code outside of scanning range
                    var lvalues = get_lvalues(candidate);
                    if (lhs instanceof AST_SymbolRef) lvalues[lhs.name] = false;
                    var replace_all = value_def;
                    if (!replace_all && lhs instanceof AST_SymbolRef) {
                        var def = lhs.definition();
                        if (def.references.length - def.replaced == (candidate instanceof AST_VarDef ? 1 : 2)) {
                            replace_all = true;
                        }
                    }
                    var side_effects = value_has_side_effects(candidate);
                    var may_throw = candidate.may_throw(compressor);
                    var funarg = candidate.name instanceof AST_SymbolFunarg;
                    var hit = funarg;
                    var abort = false, replaced = 0, can_replace = !args || !hit;
                    if (!can_replace) {
                        for (var j = compressor.self().argnames.lastIndexOf(candidate.name) + 1; !abort && j < args.length; j++) {
                            args[j].transform(scanner);
                        }
                        can_replace = true;
                    }
                    for (var i = stat_index; !abort && i < statements.length; i++) {
                        statements[i].transform(scanner);
                    }
                    if (value_def) {
                        var def = candidate.name.definition();
                        if (abort && def.references.length - def.replaced > replaced) replaced = false;
                        else {
                            abort = false;
                            hit_index = 0;
                            hit = funarg;
                            for (var i = stat_index; !abort && i < statements.length; i++) {
                                statements[i].transform(multi_replacer);
                            }
                            value_def.single_use = false;
                        }
                    }
                    if (replaced && !remove_candidate(candidate)) statements.splice(stat_index, 1);
                }
            }

            function handle_custom_scan_order(node) {
                // Skip (non-executed) functions
                if (node instanceof AST_Scope) return node;
                // Scan case expressions first in a switch statement
                if (node instanceof AST_Switch) {
                    node.expression = node.expression.transform(scanner);
                    for (var i = 0, len = node.body.length; !abort && i < len; i++) {
                        var branch = node.body[i];
                        if (branch instanceof AST_Case) {
                            if (!hit) {
                                if (branch !== hit_stack[hit_index]) continue;
                                hit_index++;
                            }
                            branch.expression = branch.expression.transform(scanner);
                            if (side_effects || !replace_all) break;
                        }
                    }
                    abort = true;
                    return node;
                }
            }

            function has_overlapping_symbol(fn, arg, fn_strict) {
                var found = false, scan_this = !(fn instanceof AST_Arrow);
                arg.walk(new TreeWalker(function(node, descend) {
                    if (found) return true;
                    if (node instanceof AST_SymbolRef && fn.variables.has(node.name)) {
                        var s = node.definition().scope;
                        if (s !== scope) while (s = s.parent_scope) {
                            if (s === scope) return true;
                        }
                        return found = true;
                    }
                    if ((fn_strict || scan_this) && node instanceof AST_This) {
                        return found = true;
                    }
                    if (node instanceof AST_Scope && !(node instanceof AST_Arrow)) {
                        var prev = scan_this;
                        scan_this = false;
                        descend();
                        scan_this = prev;
                        return true;
                    }
                }));
                return found;
            }

            function extract_args() {
                var iife, fn = compressor.self();
                if (is_func_expr(fn)
                    && !fn.name
                    && !fn.uses_arguments
                    && !fn.uses_eval
                    && (iife = compressor.parent()) instanceof AST_Call
                    && iife.expression === fn
                    && all(iife.args, function(arg) {
                        return !(arg instanceof AST_Expansion);
                    })) {
                    var fn_strict = compressor.has_directive("use strict");
                    if (fn_strict && !member(fn_strict, fn.body)) fn_strict = false;
                    var len = fn.argnames.length;
                    args = iife.args.slice(len);
                    var names = Object.create(null);
                    for (var i = len; --i >= 0;) {
                        var sym = fn.argnames[i];
                        var arg = iife.args[i];
                        args.unshift(make_node(AST_VarDef, sym, {
                            name: sym,
                            value: arg
                        }));
                        if (sym.name in names) continue;
                        names[sym.name] = true;
                        if (sym instanceof AST_Expansion) {
                            var elements = iife.args.slice(i);
                            if (all(elements, function(arg) {
                                return !has_overlapping_symbol(fn, arg, fn_strict);
                            })) {
                                candidates.unshift([ make_node(AST_VarDef, sym, {
                                    name: sym.expression,
                                    value: make_node(AST_Array, iife, {
                                        elements: elements
                                    })
                                }) ]);
                            }
                        } else {
                            if (!arg) arg = make_node(AST_Undefined, sym).transform(compressor);
                            else if (has_overlapping_symbol(fn, arg, fn_strict)) arg = null;
                            if (arg) candidates.unshift([ make_node(AST_VarDef, sym, {
                                name: sym,
                                value: arg
                            }) ]);
                        }
                    }
                }
            }

            function extract_candidates(expr) {
                hit_stack.push(expr);
                if (expr instanceof AST_Assign) {
                    if (!expr.left.has_side_effects(compressor)) {
                        candidates.push(hit_stack.slice());
                    }
                    extract_candidates(expr.right);
                } else if (expr instanceof AST_Binary) {
                    extract_candidates(expr.left);
                    extract_candidates(expr.right);
                } else if (expr instanceof AST_Call) {
                    extract_candidates(expr.expression);
                    expr.args.forEach(extract_candidates);
                } else if (expr instanceof AST_Case) {
                    extract_candidates(expr.expression);
                } else if (expr instanceof AST_Conditional) {
                    extract_candidates(expr.condition);
                    extract_candidates(expr.consequent);
                    extract_candidates(expr.alternative);
                } else if (expr instanceof AST_Definitions
                    && (compressor.option("unused") || !(expr instanceof AST_Const))) {
                    expr.definitions.forEach(extract_candidates);
                } else if (expr instanceof AST_DWLoop) {
                    extract_candidates(expr.condition);
                    if (!(expr.body instanceof AST_Block)) {
                        extract_candidates(expr.body);
                    }
                } else if (expr instanceof AST_Exit) {
                    if (expr.value) extract_candidates(expr.value);
                } else if (expr instanceof AST_For) {
                    if (expr.init) extract_candidates(expr.init);
                    if (expr.condition) extract_candidates(expr.condition);
                    if (expr.step) extract_candidates(expr.step);
                    if (!(expr.body instanceof AST_Block)) {
                        extract_candidates(expr.body);
                    }
                } else if (expr instanceof AST_ForIn) {
                    extract_candidates(expr.object);
                    if (!(expr.body instanceof AST_Block)) {
                        extract_candidates(expr.body);
                    }
                } else if (expr instanceof AST_If) {
                    extract_candidates(expr.condition);
                    if (!(expr.body instanceof AST_Block)) {
                        extract_candidates(expr.body);
                    }
                    if (expr.alternative && !(expr.alternative instanceof AST_Block)) {
                        extract_candidates(expr.alternative);
                    }
                } else if (expr instanceof AST_Sequence) {
                    expr.expressions.forEach(extract_candidates);
                } else if (expr instanceof AST_SimpleStatement) {
                    extract_candidates(expr.body);
                } else if (expr instanceof AST_Switch) {
                    extract_candidates(expr.expression);
                    expr.body.forEach(extract_candidates);
                } else if (expr instanceof AST_Unary) {
                    if (expr.operator == "++" || expr.operator == "--") {
                        candidates.push(hit_stack.slice());
                    }
                } else if (expr instanceof AST_VarDef) {
                    if (expr.value) {
                        candidates.push(hit_stack.slice());
                        extract_candidates(expr.value);
                    }
                }
                hit_stack.pop();
            }

            function find_stop(node, level, write_only) {
                var parent = scanner.parent(level);
                if (parent instanceof AST_Assign) {
                    if (write_only
                        && !(parent.left instanceof AST_PropAccess
                            || parent.left.name in lvalues)) {
                        return find_stop(parent, level + 1, write_only);
                    }
                    return node;
                }
                if (parent instanceof AST_Binary) {
                    if (write_only && (!lazy_op(parent.operator) || parent.left === node)) {
                        return find_stop(parent, level + 1, write_only);
                    }
                    return node;
                }
                if (parent instanceof AST_Call) return node;
                if (parent instanceof AST_Case) return node;
                if (parent instanceof AST_Conditional) {
                    if (write_only && parent.condition === node) {
                        return find_stop(parent, level + 1, write_only);
                    }
                    return node;
                }
                if (parent instanceof AST_Definitions) {
                    return find_stop(parent, level + 1, true);
                }
                if (parent instanceof AST_Exit) {
                    return write_only ? find_stop(parent, level + 1, write_only) : node;
                }
                if (parent instanceof AST_If) {
                    if (write_only && parent.condition === node) {
                        return find_stop(parent, level + 1, write_only);
                    }
                    return node;
                }
                if (parent instanceof AST_IterationStatement) return node;
                if (parent instanceof AST_Sequence) {
                    return find_stop(parent, level + 1, parent.tail_node() !== node);
                }
                if (parent instanceof AST_SimpleStatement) {
                    return find_stop(parent, level + 1, true);
                }
                if (parent instanceof AST_Switch) return node;
                if (parent instanceof AST_VarDef) return node;
                return null;
            }

            function mangleable_var(var_def) {
                var value = var_def.value;
                if (!(value instanceof AST_SymbolRef)) return;
                if (value.name == "arguments") return;
                var def = value.definition();
                if (def.undeclared) return;
                return value_def = def;
            }

            function get_lhs(expr) {
                if (expr instanceof AST_VarDef && expr.name instanceof AST_SymbolDeclaration) {
                    var def = expr.name.definition();
                    if (!member(expr.name, def.orig)) return;
                    var declared = def.orig.length - def.eliminated;
                    var referenced = def.references.length - def.replaced;
                    if (declared > 1 && !(expr.name instanceof AST_SymbolFunarg)
                        || (referenced > 1 ? mangleable_var(expr) : !compressor.exposed(def))) {
                        return make_node(AST_SymbolRef, expr.name, expr.name);
                    }
                } else {
                    var lhs = expr[expr instanceof AST_Assign ? "left" : "expression"];
                    return !is_ref_of(lhs, AST_SymbolConst) && lhs;
                }
            }

            function get_rvalue(expr) {
                return expr[expr instanceof AST_Assign ? "right" : "value"];
            }

            function get_lvalues(expr) {
                var lvalues = Object.create(null);
                if (expr instanceof AST_Unary) return lvalues;
                var tw = new TreeWalker(function(node, descend) {
                    var sym = node;
                    while (sym instanceof AST_PropAccess) sym = sym.expression;
                    if (sym instanceof AST_SymbolRef || sym instanceof AST_This) {
                        lvalues[sym.name] = lvalues[sym.name] || is_lhs(node, tw.parent());
                    }
                });
                get_rvalue(expr).walk(tw);
                return lvalues;
            }

            function remove_candidate(expr) {
                if (expr.name instanceof AST_SymbolFunarg) {
                    var iife = compressor.parent(), argnames = compressor.self().argnames;
                    var index = argnames.indexOf(expr.name);
                    if (index < 0) {
                        iife.args.length = Math.min(iife.args.length, argnames.length - 1);
                    } else {
                        var args = iife.args;
                        if (args[index]) args[index] = make_node(AST_Number, args[index], {
                            value: 0
                        });
                    }
                    return true;
                }
                var found = false;
                return statements[stat_index].transform(new TreeTransformer(function(node, descend, in_list) {
                    if (found) return node;
                    if (node === expr || node.body === expr) {
                        found = true;
                        if (node instanceof AST_VarDef) {
                            node.value = null;
                            return node;
                        }
                        return in_list ? MAP.skip : null;
                    }
                }, function(node) {
                    if (node instanceof AST_Sequence) switch (node.expressions.length) {
                      case 0: return null;
                      case 1: return node.expressions[0];
                    }
                }));
            }

            function value_has_side_effects(expr) {
                if (expr instanceof AST_Unary) return false;
                return get_rvalue(expr).has_side_effects(compressor);
            }

            function may_modify(sym) {
                var def = sym.definition();
                if (def.orig.length == 1 && def.orig[0] instanceof AST_SymbolDefun) return false;
                if (def.scope.get_defun_scope() !== scope) return true;
                return !all(def.references, function(ref) {
                    return ref.scope.get_defun_scope() === scope;
                });
            }

            function side_effects_external(node, lhs) {
                if (node instanceof AST_Assign) return side_effects_external(node.left, true);
                if (node instanceof AST_Unary) return side_effects_external(node.expression, true);
                if (node instanceof AST_VarDef) return node.value && side_effects_external(node.value);
                if (lhs) {
                    if (node instanceof AST_Dot) return side_effects_external(node.expression, true);
                    if (node instanceof AST_Sub) return side_effects_external(node.expression, true);
                    if (node instanceof AST_SymbolRef) return node.definition().scope !== scope;
                }
                return false;
            }
        }

        function eliminate_spurious_blocks(statements) {
            var seen_dirs = [];
            for (var i = 0; i < statements.length;) {
                var stat = statements[i];
                if (stat instanceof AST_BlockStatement && all(stat.body, can_be_evicted_from_block)) {
                    CHANGED = true;
                    eliminate_spurious_blocks(stat.body);
                    [].splice.apply(statements, [i, 1].concat(stat.body));
                    i += stat.body.length;
                } else if (stat instanceof AST_EmptyStatement) {
                    CHANGED = true;
                    statements.splice(i, 1);
                } else if (stat instanceof AST_Directive) {
                    if (seen_dirs.indexOf(stat.value) < 0) {
                        i++;
                        seen_dirs.push(stat.value);
                    } else {
                        CHANGED = true;
                        statements.splice(i, 1);
                    }
                } else i++;
            }
        }

        function handle_if_return(statements, compressor) {
            var self = compressor.self();
            var multiple_if_returns = has_multiple_if_returns(statements);
            var in_lambda = self instanceof AST_Lambda;
            for (var i = statements.length; --i >= 0;) {
                var stat = statements[i];
                var j = next_index(i);
                var next = statements[j];

                if (in_lambda && !next && stat instanceof AST_Return) {
                    if (!stat.value) {
                        CHANGED = true;
                        statements.splice(i, 1);
                        continue;
                    }
                    if (stat.value instanceof AST_UnaryPrefix && stat.value.operator == "void") {
                        CHANGED = true;
                        statements[i] = make_node(AST_SimpleStatement, stat, {
                            body: stat.value.expression
                        });
                        continue;
                    }
                }

                if (stat instanceof AST_If) {
                    var ab = aborts(stat.body);
                    if (can_merge_flow(ab)) {
                        if (ab.label) {
                            remove(ab.label.thedef.references, ab);
                        }
                        CHANGED = true;
                        stat = stat.clone();
                        stat.condition = stat.condition.negate(compressor);
                        var body = as_statement_array_with_return(stat.body, ab);
                        stat.body = make_node(AST_BlockStatement, stat, {
                            body: as_statement_array(stat.alternative).concat(extract_functions())
                        });
                        stat.alternative = make_node(AST_BlockStatement, stat, {
                            body: body
                        });
                        statements[i] = stat.transform(compressor);
                        continue;
                    }

                    var ab = aborts(stat.alternative);
                    if (can_merge_flow(ab)) {
                        if (ab.label) {
                            remove(ab.label.thedef.references, ab);
                        }
                        CHANGED = true;
                        stat = stat.clone();
                        stat.body = make_node(AST_BlockStatement, stat.body, {
                            body: as_statement_array(stat.body).concat(extract_functions())
                        });
                        var body = as_statement_array_with_return(stat.alternative, ab);
                        stat.alternative = make_node(AST_BlockStatement, stat.alternative, {
                            body: body
                        });
                        statements[i] = stat.transform(compressor);
                        continue;
                    }
                }

                if (stat instanceof AST_If && stat.body instanceof AST_Return) {
                    var value = stat.body.value;
                    //---
                    // pretty silly case, but:
                    // if (foo()) return; return; ==> foo(); return;
                    if (!value && !stat.alternative
                        && (in_lambda && !next || next instanceof AST_Return && !next.value)) {
                        CHANGED = true;
                        statements[i] = make_node(AST_SimpleStatement, stat.condition, {
                            body: stat.condition
                        });
                        continue;
                    }
                    //---
                    // if (foo()) return x; return y; ==> return foo() ? x : y;
                    if (value && !stat.alternative && next instanceof AST_Return && next.value) {
                        CHANGED = true;
                        stat = stat.clone();
                        stat.alternative = next;
                        statements.splice(i, 1, stat.transform(compressor));
                        statements.splice(j, 1);
                        continue;
                    }
                    //---
                    // if (foo()) return x; [ return ; ] ==> return foo() ? x : undefined;
                    if (value && !stat.alternative
                        && (!next && in_lambda && multiple_if_returns
                            || next instanceof AST_Return)) {
                        CHANGED = true;
                        stat = stat.clone();
                        stat.alternative = next || make_node(AST_Return, stat, {
                            value: null
                        });
                        statements.splice(i, 1, stat.transform(compressor));
                        if (next) statements.splice(j, 1);
                        continue;
                    }
                    //---
                    // if (a) return b; if (c) return d; e; ==> return a ? b : c ? d : void e;
                    //
                    // if sequences is not enabled, this can lead to an endless loop (issue #866).
                    // however, with sequences on this helps producing slightly better output for
                    // the example code.
                    var prev = statements[prev_index(i)];
                    if (compressor.option("sequences") && in_lambda && !stat.alternative
                        && prev instanceof AST_If && prev.body instanceof AST_Return
                        && next_index(j) == statements.length && next instanceof AST_SimpleStatement) {
                        CHANGED = true;
                        stat = stat.clone();
                        stat.alternative = make_node(AST_BlockStatement, next, {
                            body: [
                                next,
                                make_node(AST_Return, next, {
                                    value: null
                                })
                            ]
                        });
                        statements.splice(i, 1, stat.transform(compressor));
                        statements.splice(j, 1);
                        continue;
                    }
                }
            }

            function has_multiple_if_returns(statements) {
                var n = 0;
                for (var i = statements.length; --i >= 0;) {
                    var stat = statements[i];
                    if (stat instanceof AST_If && stat.body instanceof AST_Return) {
                        if (++n > 1) return true;
                    }
                }
                return false;
            }

            function is_return_void(value) {
                return !value || value instanceof AST_UnaryPrefix && value.operator == "void";
            }

            function can_merge_flow(ab) {
                if (!ab) return false;
                for (var j = i + 1, len = statements.length; j < len; j++) {
                    var stat = statements[j];
                    if (stat instanceof AST_Const || stat instanceof AST_Let) return false;
                }
                var lct = ab instanceof AST_LoopControl ? compressor.loopcontrol_target(ab) : null;
                return ab instanceof AST_Return && in_lambda && is_return_void(ab.value)
                    || ab instanceof AST_Continue && self === loop_body(lct)
                    || ab instanceof AST_Break && lct instanceof AST_BlockStatement && self === lct;
            }

            function extract_functions() {
                var tail = statements.slice(i + 1);
                statements.length = i + 1;
                return tail.filter(function(stat) {
                    if (stat instanceof AST_Defun) {
                        statements.push(stat);
                        return false;
                    }
                    return true;
                });
            }

            function as_statement_array_with_return(node, ab) {
                var body = as_statement_array(node).slice(0, -1);
                if (ab.value) {
                    body.push(make_node(AST_SimpleStatement, ab.value, {
                        body: ab.value.expression
                    }));
                }
                return body;
            }

            function next_index(i) {
                for (var j = i + 1, len = statements.length; j < len; j++) {
                    var stat = statements[j];
                    if (!(stat instanceof AST_Var && declarations_only(stat))) {
                        break;
                    }
                }
                return j;
            }

            function prev_index(i) {
                for (var j = i; --j >= 0;) {
                    var stat = statements[j];
                    if (!(stat instanceof AST_Var && declarations_only(stat))) {
                        break;
                    }
                }
                return j;
            }
        }

        function eliminate_dead_code(statements, compressor) {
            var has_quit;
            var self = compressor.self();
            for (var i = 0, n = 0, len = statements.length; i < len; i++) {
                var stat = statements[i];
                if (stat instanceof AST_LoopControl) {
                    var lct = compressor.loopcontrol_target(stat);
                    if (stat instanceof AST_Break
                            && !(lct instanceof AST_IterationStatement)
                            && loop_body(lct) === self
                        || stat instanceof AST_Continue
                            && loop_body(lct) === self) {
                        if (stat.label) {
                            remove(stat.label.thedef.references, stat);
                        }
                    } else {
                        statements[n++] = stat;
                    }
                } else {
                    statements[n++] = stat;
                }
                if (aborts(stat)) {
                    has_quit = statements.slice(i + 1);
                    break;
                }
            }
            statements.length = n;
            CHANGED = n != len;
            if (has_quit) has_quit.forEach(function(stat) {
                extract_declarations_from_unreachable_code(compressor, stat, statements);
            });
        }

        function declarations_only(node) {
            return all(node.definitions, function(var_def) {
                return !var_def.value;
            });
        }

        function sequencesize(statements, compressor) {
            if (statements.length < 2) return;
            var seq = [], n = 0;
            function push_seq() {
                if (!seq.length) return;
                var body = make_sequence(seq[0], seq);
                statements[n++] = make_node(AST_SimpleStatement, body, { body: body });
                seq = [];
            }
            for (var i = 0, len = statements.length; i < len; i++) {
                var stat = statements[i];
                if (stat instanceof AST_SimpleStatement) {
                    if (seq.length >= compressor.sequences_limit) push_seq();
                    var body = stat.body;
                    if (seq.length > 0) body = body.drop_side_effect_free(compressor);
                    if (body) merge_sequence(seq, body);
                } else if (stat instanceof AST_Definitions && declarations_only(stat)
                    || stat instanceof AST_Defun) {
                    statements[n++] = stat;
                } else {
                    push_seq();
                    statements[n++] = stat;
                }
            }
            push_seq();
            statements.length = n;
            if (n != len) CHANGED = true;
        }

        function to_simple_statement(block, decls) {
            if (!(block instanceof AST_BlockStatement)) return block;
            var stat = null;
            for (var i = 0, len = block.body.length; i < len; i++) {
                var line = block.body[i];
                if (line instanceof AST_Var && declarations_only(line)) {
                    decls.push(line);
                } else if (stat) {
                    return false;
                } else {
                    stat = line;
                }
            }
            return stat;
        }

        function sequencesize_2(statements, compressor) {
            function cons_seq(right) {
                n--;
                CHANGED = true;
                var left = prev.body;
                return make_sequence(left, [ left, right ]).transform(compressor);
            };
            var n = 0, prev;
            for (var i = 0; i < statements.length; i++) {
                var stat = statements[i];
                if (prev) {
                    if (stat instanceof AST_Exit) {
                        stat.value = cons_seq(stat.value || make_node(AST_Undefined, stat).transform(compressor));
                    } else if (stat instanceof AST_For) {
                        if (!(stat.init instanceof AST_Definitions)) {
                            var abort = false;
                            prev.body.walk(new TreeWalker(function(node) {
                                if (abort || node instanceof AST_Scope) return true;
                                if (node instanceof AST_Binary && node.operator == "in") {
                                    abort = true;
                                    return true;
                                }
                            }));
                            if (!abort) {
                                if (stat.init) stat.init = cons_seq(stat.init);
                                else {
                                    stat.init = prev.body;
                                    n--;
                                    CHANGED = true;
                                }
                            }
                        }
                    } else if (stat instanceof AST_ForIn) {
                        if (!(stat.init instanceof AST_Const) && !(stat.init instanceof AST_Let)) {
                            stat.object = cons_seq(stat.object);
                        }
                    } else if (stat instanceof AST_If) {
                        stat.condition = cons_seq(stat.condition);
                    } else if (stat instanceof AST_Switch) {
                        stat.expression = cons_seq(stat.expression);
                    } else if (stat instanceof AST_With) {
                        stat.expression = cons_seq(stat.expression);
                    }
                }
                if (compressor.option("conditionals") && stat instanceof AST_If) {
                    var decls = [];
                    var body = to_simple_statement(stat.body, decls);
                    var alt = to_simple_statement(stat.alternative, decls);
                    if (body !== false && alt !== false && decls.length > 0) {
                        var len = decls.length;
                        decls.push(make_node(AST_If, stat, {
                            condition: stat.condition,
                            body: body || make_node(AST_EmptyStatement, stat.body),
                            alternative: alt
                        }));
                        decls.unshift(n, 1);
                        [].splice.apply(statements, decls);
                        i += len;
                        n += len + 1;
                        prev = null;
                        CHANGED = true;
                        continue;
                    }
                }
                statements[n++] = stat;
                prev = stat instanceof AST_SimpleStatement ? stat : null;
            }
            statements.length = n;
        }

        function join_object_assignments(defn, body) {
            if (!(defn instanceof AST_Definitions)) return;
            var def = defn.definitions[defn.definitions.length - 1];
            if (!(def.value instanceof AST_Object)) return;
            var exprs;
            if (body instanceof AST_Assign) {
                exprs = [ body ];
            } else if (body instanceof AST_Sequence) {
                exprs = body.expressions.slice();
            }
            if (!exprs) return;
            var trimmed = false;
            do {
                var node = exprs[0];
                if (!(node instanceof AST_Assign)) break;
                if (node.operator != "=") break;
                if (!(node.left instanceof AST_PropAccess)) break;
                var sym = node.left.expression;
                if (!(sym instanceof AST_SymbolRef)) break;
                if (def.name.name != sym.name) break;
                if (!node.right.is_constant_expression(scope)) break;
                var prop = node.left.property;
                if (prop instanceof AST_Node) {
                    prop = prop.evaluate(compressor);
                }
                if (prop instanceof AST_Node) break;
                prop = "" + prop;
                if (compressor.option("ecma") < 6 && compressor.has_directive("use strict")) {
                    if (!all(def.value.properties, function(node) {
                        return node.key != prop && node.key.name != prop;
                    })) break;
                }
                def.value.properties.push(make_node(AST_ObjectKeyVal, node, {
                    key: prop,
                    value: node.right
                }));
                exprs.shift();
                trimmed = true;
            } while (exprs.length);
            return trimmed && exprs;
        }

        function join_consecutive_vars(statements) {
            var defs;
            for (var i = 0, j = -1, len = statements.length; i < len; i++) {
                var stat = statements[i];
                var prev = statements[j];
                if (stat instanceof AST_Definitions) {
                    if (prev && prev.TYPE == stat.TYPE) {
                        prev.definitions = prev.definitions.concat(stat.definitions);
                        CHANGED = true;
                    } else if (defs && defs.TYPE == stat.TYPE && declarations_only(stat)) {
                        defs.definitions = defs.definitions.concat(stat.definitions);
                        CHANGED = true;
                    } else {
                        statements[++j] = stat;
                        defs = stat;
                    }
                } else if (stat instanceof AST_Exit) {
                    stat.value = extract_object_assignments(stat.value);
                } else if (stat instanceof AST_For) {
                    var exprs = join_object_assignments(prev, stat.init);
                    if (exprs) {
                        CHANGED = true;
                        stat.init = exprs.length ? make_sequence(stat.init, exprs) : null;
                        statements[++j] = stat;
                    } else if (prev instanceof AST_Var && (!stat.init || stat.init.TYPE == prev.TYPE)) {
                        if (stat.init) {
                            prev.definitions = prev.definitions.concat(stat.init.definitions);
                        }
                        stat.init = prev;
                        statements[j] = stat;
                        CHANGED = true;
                    } else if (defs && stat.init && defs.TYPE == stat.init.TYPE && declarations_only(stat.init)) {
                        defs.definitions = defs.definitions.concat(stat.init.definitions);
                        stat.init = null;
                        statements[++j] = stat;
                        CHANGED = true;
                    } else {
                        statements[++j] = stat;
                    }
                } else if (stat instanceof AST_ForIn) {
                    stat.object = extract_object_assignments(stat.object);
                } else if (stat instanceof AST_If) {
                    stat.condition = extract_object_assignments(stat.condition);
                } else if (stat instanceof AST_SimpleStatement) {
                    var exprs = join_object_assignments(prev, stat.body);
                    if (exprs) {
                        CHANGED = true;
                        if (!exprs.length) continue;
                        stat.body = make_sequence(stat.body, exprs);
                    }
                    statements[++j] = stat;
                } else if (stat instanceof AST_Switch) {
                    stat.expression = extract_object_assignments(stat.expression);
                } else if (stat instanceof AST_With) {
                    stat.expression = extract_object_assignments(stat.expression);
                } else {
                    statements[++j] = stat;
                }
            }
            statements.length = j + 1;

            function extract_object_assignments(value) {
                statements[++j] = stat;
                var exprs = join_object_assignments(prev, value);
                if (exprs) {
                    CHANGED = true;
                    if (exprs.length) {
                        return make_sequence(value, exprs);
                    } else if (value instanceof AST_Sequence) {
                        return value.tail_node().left;
                    } else {
                        return value.left;
                    }
                }
                return value;
            }
        }
    }

    function extract_declarations_from_unreachable_code(compressor, stat, target) {
        if (!(stat instanceof AST_Defun)) {
            compressor.warn("Dropping unreachable code [{file}:{line},{col}]", stat.start);
        }
        stat.walk(new TreeWalker(function(node){
            if (node instanceof AST_Var) {
                compressor.warn("Declarations in unreachable code! [{file}:{line},{col}]", node.start);
                node.remove_initializers();
                target.push(node);
                return true;
            }
            if (node instanceof AST_Defun && (node === stat || !compressor.has_directive("use strict"))) {
                target.push(node === stat ? node : make_node(AST_Var, node, {
                    definitions: [
                        make_node(AST_VarDef, node, {
                            name: make_node(AST_SymbolVar, node.name, node.name),
                            value: null
                        })
                    ]
                }));
                return true;
            }
            if (node instanceof AST_Scope) {
                return true;
            }
        }));
    };

    function get_value(key) {
        if (key instanceof AST_Constant) {
            return key.getValue();
        }
        if (key instanceof AST_UnaryPrefix
            && key.operator == "void"
            && key.expression instanceof AST_Constant) {
            return;
        }
        return key;
    }

    function is_undefined(node, compressor) {
        return node.is_undefined
            || node instanceof AST_Undefined
            || node instanceof AST_UnaryPrefix
                && node.operator == "void"
                && !node.expression.has_side_effects(compressor);
    }

    // may_throw_on_access()
    // returns true if this node may be null, undefined or contain `AST_Accessor`
    (function(def) {
        AST_Node.DEFMETHOD("may_throw_on_access", function(compressor) {
            return !compressor.option("pure_getters")
                || this._dot_throw(compressor);
        });

        function is_strict(compressor) {
            return /strict/.test(compressor.option("pure_getters"));
        }

        def(AST_Node, is_strict);
        def(AST_Null, return_true);
        def(AST_Undefined, return_true);
        def(AST_Constant, return_false);
        def(AST_Array, return_false);
        def(AST_Object, function(compressor) {
            if (!is_strict(compressor)) return false;
            for (var i = this.properties.length; --i >=0;)
                if (this.properties[i]._dot_throw(compressor)) return true;
            return false;
        });
        def(AST_ObjectProperty, return_false);
        def(AST_ObjectGetter, return_true);
        def(AST_Expansion, function(compressor) {
            return this.expression._dot_throw(compressor);
        });
        def(AST_Function, return_false);
        def(AST_Arrow, return_false);
        def(AST_UnaryPostfix, return_false);
        def(AST_UnaryPrefix, function() {
            return this.operator == "void";
        });
        def(AST_Binary, function(compressor) {
            return (this.operator == "&&" || this.operator == "||")
                && (this.left._dot_throw(compressor) || this.right._dot_throw(compressor));
        })
        def(AST_Assign, function(compressor) {
            return this.operator == "="
                && this.right._dot_throw(compressor);
        })
        def(AST_Conditional, function(compressor) {
            return this.consequent._dot_throw(compressor)
                || this.alternative._dot_throw(compressor);
        })
        def(AST_Dot, function(compressor) {
            if (!is_strict(compressor)) return false;
            if (this.expression instanceof AST_Function && this.property == "prototype") return false;
            return true;
        });
        def(AST_Sequence, function(compressor) {
            return this.tail_node()._dot_throw(compressor);
        });
        def(AST_SymbolRef, function(compressor) {
            if (this.is_undefined) return true;
            if (!is_strict(compressor)) return false;
            if (is_undeclared_ref(this) && this.is_declared(compressor)) return false;
            if (this.is_immutable()) return false;
            var fixed = this.fixed_value();
            return !fixed || fixed._dot_throw(compressor);
        });
    })(function(node, func) {
        node.DEFMETHOD("_dot_throw", func);
    });

    /* -----[ boolean/negation helpers ]----- */

    // methods to determine whether an expression has a boolean result type
    (function(def){
        var unary_bool = [ "!", "delete" ];
        var binary_bool = [ "in", "instanceof", "==", "!=", "===", "!==", "<", "<=", ">=", ">" ];
        def(AST_Node, return_false);
        def(AST_UnaryPrefix, function(){
            return member(this.operator, unary_bool);
        });
        def(AST_Binary, function(){
            return member(this.operator, binary_bool)
                || lazy_op(this.operator)
                    && this.left.is_boolean()
                    && this.right.is_boolean();
        });
        def(AST_Conditional, function(){
            return this.consequent.is_boolean() && this.alternative.is_boolean();
        });
        def(AST_Assign, function(){
            return this.operator == "=" && this.right.is_boolean();
        });
        def(AST_Sequence, function(){
            return this.tail_node().is_boolean();
        });
        def(AST_True, return_true);
        def(AST_False, return_true);
    })(function(node, func){
        node.DEFMETHOD("is_boolean", func);
    });

    // methods to determine if an expression has a numeric result type
    (function(def){
        def(AST_Node, return_false);
        def(AST_Number, return_true);
        var unary = makePredicate("+ - ~ ++ --");
        def(AST_Unary, function(){
            return unary(this.operator);
        });
        var binary = makePredicate("- * / % & | ^ << >> >>>");
        def(AST_Binary, function(compressor){
            return binary(this.operator) || this.operator == "+"
                && this.left.is_number(compressor)
                && this.right.is_number(compressor);
        });
        def(AST_Assign, function(compressor){
            return binary(this.operator.slice(0, -1))
                || this.operator == "=" && this.right.is_number(compressor);
        });
        def(AST_Sequence, function(compressor){
            return this.tail_node().is_number(compressor);
        });
        def(AST_Conditional, function(compressor){
            return this.consequent.is_number(compressor) && this.alternative.is_number(compressor);
        });
    })(function(node, func){
        node.DEFMETHOD("is_number", func);
    });

    // methods to determine if an expression has a string result type
    (function(def){
        def(AST_Node, return_false);
        def(AST_String, return_true);
        def(AST_TemplateString, function(){
            return this.segments.length === 1;
        });
        def(AST_UnaryPrefix, function(){
            return this.operator == "typeof";
        });
        def(AST_Binary, function(compressor){
            return this.operator == "+" &&
                (this.left.is_string(compressor) || this.right.is_string(compressor));
        });
        def(AST_Assign, function(compressor){
            return (this.operator == "=" || this.operator == "+=") && this.right.is_string(compressor);
        });
        def(AST_Sequence, function(compressor){
            return this.tail_node().is_string(compressor);
        });
        def(AST_Conditional, function(compressor){
            return this.consequent.is_string(compressor) && this.alternative.is_string(compressor);
        });
    })(function(node, func){
        node.DEFMETHOD("is_string", func);
    });

    var lazy_op = makePredicate("&& ||");
    var unary_side_effects = makePredicate("delete ++ --");

    function is_lhs(node, parent) {
        if (parent instanceof AST_Unary && unary_side_effects(parent.operator)) return parent.expression;
        if (parent instanceof AST_Assign && parent.left === node) return node;
    }

    (function(def){
        AST_Node.DEFMETHOD("resolve_defines", function(compressor) {
            if (!compressor.option("global_defs")) return;
            var def = this._find_defs(compressor, "");
            if (def) {
                var node, parent = this, level = 0;
                do {
                    node = parent;
                    parent = compressor.parent(level++);
                } while (parent instanceof AST_PropAccess && parent.expression === node);
                if (is_lhs(node, parent)) {
                    compressor.warn('global_defs ' + this.print_to_string() + ' redefined [{file}:{line},{col}]', this.start);
                } else {
                    return def;
                }
            }
        });
        function to_node(value, orig) {
            if (value instanceof AST_Node) return make_node(value.CTOR, orig, value);
            if (Array.isArray(value)) return make_node(AST_Array, orig, {
                elements: value.map(function(value) {
                    return to_node(value, orig);
                })
            });
            if (value && typeof value == "object") {
                var props = [];
                for (var key in value) if (HOP(value, key)) {
                    props.push(make_node(AST_ObjectKeyVal, orig, {
                        key: key,
                        value: to_node(value[key], orig)
                    }));
                }
                return make_node(AST_Object, orig, {
                    properties: props
                });
            }
            return make_node_from_constant(value, orig);
        }
        def(AST_Node, noop);
        def(AST_Dot, function(compressor, suffix){
            return this.expression._find_defs(compressor, "." + this.property + suffix);
        });
        def(AST_SymbolRef, function(compressor, suffix){
            if (!this.global()) return;
            var name;
            var defines = compressor.option("global_defs");
            if (defines && HOP(defines, (name = this.name + suffix))) {
                var node = to_node(defines[name], this);
                var top = compressor.find_parent(AST_Toplevel);
                node.walk(new TreeWalker(function(node) {
                    if (node instanceof AST_SymbolRef) {
                        node.scope = top;
                        node.thedef = top.def_global(node);
                    }
                }));
                return node;
            }
        });
    })(function(node, func){
        node.DEFMETHOD("_find_defs", func);
    });

    function best_of_expression(ast1, ast2) {
        return ast1.print_to_string().length >
            ast2.print_to_string().length
            ? ast2 : ast1;
    }

    function best_of_statement(ast1, ast2) {
        return best_of_expression(make_node(AST_SimpleStatement, ast1, {
            body: ast1
        }), make_node(AST_SimpleStatement, ast2, {
            body: ast2
        })).body;
    }

    function best_of(compressor, ast1, ast2) {
        return (first_in_statement(compressor) ? best_of_statement : best_of_expression)(ast1, ast2);
    }

    function convert_to_predicate(obj) {
        for (var key in obj) {
            obj[key] = makePredicate(obj[key]);
        }
    }

    var object_fns = [
        "constructor",
        "toString",
        "valueOf",
    ];
    var native_fns = {
        Array: [
            "indexOf",
            "join",
            "lastIndexOf",
            "slice",
        ].concat(object_fns),
        Boolean: object_fns,
        Number: [
            "toExponential",
            "toFixed",
            "toPrecision",
        ].concat(object_fns),
        Object: object_fns,
        RegExp: [
            "test",
        ].concat(object_fns),
        String: [
            "charAt",
            "charCodeAt",
            "concat",
            "indexOf",
            "italics",
            "lastIndexOf",
            "match",
            "replace",
            "search",
            "slice",
            "split",
            "substr",
            "substring",
            "toLowerCase",
            "toUpperCase",
            "trim",
        ].concat(object_fns),
    };
    convert_to_predicate(native_fns);
    var static_fns = {
        Array: [
            "isArray",
        ],
        Math: [
            "abs",
            "acos",
            "asin",
            "atan",
            "ceil",
            "cos",
            "exp",
            "floor",
            "log",
            "round",
            "sin",
            "sqrt",
            "tan",
            "atan2",
            "pow",
            "max",
            "min",
        ],
        Number: [
            "isFinite",
            "isNaN",
        ],
        Object: [
            "create",
            "getOwnPropertyDescriptor",
            "getOwnPropertyNames",
            "getPrototypeOf",
            "isExtensible",
            "isFrozen",
            "isSealed",
            "keys",
        ],
        String: [
            "fromCharCode",
        ],
    };
    convert_to_predicate(static_fns);

    // methods to evaluate a constant expression
    (function(def){
        // If the node has been successfully reduced to a constant,
        // then its value is returned; otherwise the element itself
        // is returned.
        // They can be distinguished as constant value is never a
        // descendant of AST_Node.
        AST_Node.DEFMETHOD("evaluate", function(compressor){
            if (!compressor.option("evaluate")) return this;
            var val = this._eval(compressor, 1);
            return !val || val instanceof RegExp || typeof val != "object" ? val : this;
        });
        var unaryPrefix = makePredicate("! ~ - + void");
        AST_Node.DEFMETHOD("is_constant", function(){
            // Accomodate when compress option evaluate=false
            // as well as the common constant expressions !0 and -1
            if (this instanceof AST_Constant) {
                return !(this instanceof AST_RegExp);
            } else {
                return this instanceof AST_UnaryPrefix
                    && this.expression instanceof AST_Constant
                    && unaryPrefix(this.operator);
            }
        });
        def(AST_Statement, function(){
            throw new Error(string_template("Cannot evaluate a statement [{file}:{line},{col}]", this.start));
        });
        def(AST_Lambda, return_this);
        def(AST_Class, return_this);
        def(AST_Node, return_this);
        def(AST_Constant, function(){
            return this.getValue();
        });
        def(AST_TemplateString, function() {
            if (this.segments.length !== 1) return this;
            return this.segments[0].value;
        });
        def(AST_Array, function(compressor, depth) {
            if (compressor.option("unsafe")) {
                var elements = [];
                for (var i = 0, len = this.elements.length; i < len; i++) {
                    var element = this.elements[i];
                    if (element instanceof AST_Function) {
                        elements.push(element);
                        continue;
                    }
                    var value = element._eval(compressor, depth);
                    if (element === value) return this;
                    elements.push(value);
                }
                return elements;
            }
            return this;
        });
        def(AST_Object, function(compressor, depth) {
            if (compressor.option("unsafe")) {
                var val = {};
                for (var i = 0, len = this.properties.length; i < len; i++) {
                    var prop = this.properties[i];
                    if (prop instanceof AST_Expansion) return this;
                    var key = prop.key;
                    if (key instanceof AST_Symbol) {
                        key = key.name;
                    } else if (key instanceof AST_Node) {
                        key = key._eval(compressor, depth);
                        if (key === prop.key) return this;
                    }
                    if (typeof Object.prototype[key] === 'function') {
                        return this;
                    }
                    if (prop.value instanceof AST_Function) continue;
                    val[key] = prop.value._eval(compressor, depth);
                    if (val[key] === prop.value) return this;
                }
                return val;
            }
            return this;
        });
        def(AST_UnaryPrefix, function(compressor, depth) {
            var e = this.expression;
            // Function would be evaluated to an array and so typeof would
            // incorrectly return 'object'. Hence making is a special case.
            if (compressor.option("typeofs")
                && this.operator == "typeof"
                && (e instanceof AST_Lambda
                    || e instanceof AST_SymbolRef
                        && e.fixed_value() instanceof AST_Lambda)) {
                return typeof function(){};
            }
            e = e._eval(compressor, depth);
            if (e === this.expression) return this;
            switch (this.operator) {
              case "!": return !e;
              case "typeof":
                // typeof <RegExp> returns "object" or "function" on different platforms
                // so cannot evaluate reliably
                if (e instanceof RegExp) return this;
                return typeof e;
              case "void": return void e;
              case "~": return ~e;
              case "-": return -e;
              case "+": return +e;
            }
            return this;
        });
        def(AST_Binary, function(compressor, depth) {
            var left = this.left._eval(compressor, depth);
            if (left === this.left) return this;
            var right = this.right._eval(compressor, depth);
            if (right === this.right) return this;
            var result;
            switch (this.operator) {
              case "&&"  : result = left &&  right; break;
              case "||"  : result = left ||  right; break;
              case "|"   : result = left |   right; break;
              case "&"   : result = left &   right; break;
              case "^"   : result = left ^   right; break;
              case "+"   : result = left +   right; break;
              case "*"   : result = left *   right; break;
              case "**"  : result = Math.pow(left, right); break;
              case "/"   : result = left /   right; break;
              case "%"   : result = left %   right; break;
              case "-"   : result = left -   right; break;
              case "<<"  : result = left <<  right; break;
              case ">>"  : result = left >>  right; break;
              case ">>>" : result = left >>> right; break;
              case "=="  : result = left ==  right; break;
              case "===" : result = left === right; break;
              case "!="  : result = left !=  right; break;
              case "!==" : result = left !== right; break;
              case "<"   : result = left <   right; break;
              case "<="  : result = left <=  right; break;
              case ">"   : result = left >   right; break;
              case ">="  : result = left >=  right; break;
              default:
                  return this;
            }
            if (isNaN(result) && compressor.find_parent(AST_With)) {
                // leave original expression as is
                return this;
            }
            return result;
        });
        def(AST_Conditional, function(compressor, depth) {
            var condition = this.condition._eval(compressor, depth);
            if (condition === this.condition) return this;
            var node = condition ? this.consequent : this.alternative;
            var value = node._eval(compressor, depth);
            return value === node ? this : value;
        });
        def(AST_SymbolRef, function(compressor, depth) {
            var fixed = this.fixed_value();
            if (!fixed) return this;
            var value;
            if (HOP(fixed, "_eval")) {
                value = fixed._eval();
            } else {
                this._eval = return_this;
                value = fixed._eval(compressor, depth);
                delete this._eval;
                if (value === fixed) return this;
                fixed._eval = function() {
                    return value;
                };
            }
            if (value && typeof value == "object") {
                var escaped = this.definition().escaped;
                if (escaped && depth > escaped) return this;
            }
            return value;
        });
        var global_objs = {
            Array: Array,
            Math: Math,
            Number: Number,
            Object: Object,
            String: String,
        };
        var static_values = {
            Math: [
                "E",
                "LN10",
                "LN2",
                "LOG2E",
                "LOG10E",
                "PI",
                "SQRT1_2",
                "SQRT2",
            ],
            Number: [
                "MAX_VALUE",
                "MIN_VALUE",
                "NaN",
                "NEGATIVE_INFINITY",
                "POSITIVE_INFINITY",
            ],
        };
        convert_to_predicate(static_values);
        def(AST_PropAccess, function(compressor, depth) {
            if (compressor.option("unsafe")) {
                var key = this.property;
                if (key instanceof AST_Node) {
                    key = key._eval(compressor, depth);
                    if (key === this.property) return this;
                }
                var exp = this.expression;
                var val;
                if (is_undeclared_ref(exp)) {
                    if (!(static_values[exp.name] || return_false)(key)) return this;
                    val = global_objs[exp.name];
                } else {
                    val = exp._eval(compressor, depth + 1);
                    if (!val || val === exp || !HOP(val, key)) return this;
                }
                return val[key];
            }
            return this;
        });
        def(AST_Call, function(compressor, depth) {
            var exp = this.expression;
            if (compressor.option("unsafe") && exp instanceof AST_PropAccess) {
                var key = exp.property;
                if (key instanceof AST_Node) {
                    key = key._eval(compressor, depth);
                    if (key === exp.property) return this;
                }
                var val;
                var e = exp.expression;
                if (is_undeclared_ref(e)) {
                    if (!(static_fns[e.name] || return_false)(key)) return this;
                    val = global_objs[e.name];
                } else {
                    val = e._eval(compressor, depth + 1);
                    if (val === e || !(val && native_fns[val.constructor.name] || return_false)(key)) return this;
                }
                var args = [];
                for (var i = 0, len = this.args.length; i < len; i++) {
                    var arg = this.args[i];
                    var value = arg._eval(compressor, depth);
                    if (arg === value) return this;
                    args.push(value);
                }
                try {
                    return val[key].apply(val, args);
                } catch (ex) {
                    compressor.warn("Error evaluating {code} [{file}:{line},{col}]", {
                        code: this.print_to_string(),
                        file: this.start.file,
                        line: this.start.line,
                        col: this.start.col
                    });
                }
            }
            return this;
        });
        def(AST_New, return_this);
    })(function(node, func){
        node.DEFMETHOD("_eval", func);
    });

    // method to negate an expression
    (function(def){
        function basic_negation(exp) {
            return make_node(AST_UnaryPrefix, exp, {
                operator: "!",
                expression: exp
            });
        }
        function best(orig, alt, first_in_statement) {
            var negated = basic_negation(orig);
            if (first_in_statement) {
                var stat = make_node(AST_SimpleStatement, alt, {
                    body: alt
                });
                return best_of_expression(negated, stat) === stat ? alt : negated;
            }
            return best_of_expression(negated, alt);
        }
        def(AST_Node, function(){
            return basic_negation(this);
        });
        def(AST_Statement, function(){
            throw new Error("Cannot negate a statement");
        });
        def(AST_Function, function(){
            return basic_negation(this);
        });
        def(AST_Arrow, function(){
            return basic_negation(this);
        });
        def(AST_UnaryPrefix, function(){
            if (this.operator == "!")
                return this.expression;
            return basic_negation(this);
        });
        def(AST_Sequence, function(compressor){
            var expressions = this.expressions.slice();
            expressions.push(expressions.pop().negate(compressor));
            return make_sequence(this, expressions);
        });
        def(AST_Conditional, function(compressor, first_in_statement){
            var self = this.clone();
            self.consequent = self.consequent.negate(compressor);
            self.alternative = self.alternative.negate(compressor);
            return best(this, self, first_in_statement);
        });
        def(AST_Binary, function(compressor, first_in_statement){
            var self = this.clone(), op = this.operator;
            if (compressor.option("unsafe_comps")) {
                switch (op) {
                  case "<=" : self.operator = ">"  ; return self;
                  case "<"  : self.operator = ">=" ; return self;
                  case ">=" : self.operator = "<"  ; return self;
                  case ">"  : self.operator = "<=" ; return self;
                }
            }
            switch (op) {
              case "==" : self.operator = "!="; return self;
              case "!=" : self.operator = "=="; return self;
              case "===": self.operator = "!=="; return self;
              case "!==": self.operator = "==="; return self;
              case "&&":
                self.operator = "||";
                self.left = self.left.negate(compressor, first_in_statement);
                self.right = self.right.negate(compressor);
                return best(this, self, first_in_statement);
              case "||":
                self.operator = "&&";
                self.left = self.left.negate(compressor, first_in_statement);
                self.right = self.right.negate(compressor);
                return best(this, self, first_in_statement);
            }
            return basic_negation(this);
        });
    })(function(node, func){
        node.DEFMETHOD("negate", function(compressor, first_in_statement){
            return func.call(this, compressor, first_in_statement);
        });
    });

    var global_pure_fns = makePredicate("Boolean decodeURI decodeURIComponent Date encodeURI encodeURIComponent Error escape EvalError isFinite isNaN Number Object parseFloat parseInt RangeError ReferenceError String SyntaxError TypeError unescape URIError");
    AST_Call.DEFMETHOD("is_expr_pure", function(compressor) {
        if (compressor.option("unsafe")) {
            var expr = this.expression;
            if (is_undeclared_ref(expr) && global_pure_fns(expr.name)) return true;
            if (expr instanceof AST_Dot
                && is_undeclared_ref(expr.expression)
                && (static_fns[expr.expression.name] || return_false)(expr.property)) {
                return true;
            }
        }
        return this.pure || !compressor.pure_funcs(this);
    });
    AST_Node.DEFMETHOD("is_call_pure", return_false);
    AST_Dot.DEFMETHOD("is_call_pure", function(compressor) {
        if (!compressor.option("unsafe")) return;
        var expr = this.expression;
        var fns = return_false;
        if (expr instanceof AST_Array) {
            fns = native_fns.Array;
        } else if (expr.is_boolean()) {
            fns = native_fns.Boolean;
        } else if (expr.is_number(compressor)) {
            fns = native_fns.Number;
        } else if (expr instanceof AST_RegExp) {
            fns = native_fns.RegExp;
        } else if (expr.is_string(compressor)) {
            fns = native_fns.String;
        } else if (!this.may_throw_on_access(compressor)) {
            fns = native_fns.Object;
        }
        return fns(this.property);
    });

    // determine if expression has side effects
    (function(def){
        def(AST_Node, return_true);

        def(AST_EmptyStatement, return_false);
        def(AST_Constant, return_false);
        def(AST_This, return_false);

        function any(list, compressor) {
            for (var i = list.length; --i >= 0;)
                if (list[i].has_side_effects(compressor))
                    return true;
            return false;
        }

        def(AST_Block, function(compressor){
            return any(this.body, compressor);
        });
        def(AST_Call, function(compressor){
            if (!this.is_expr_pure(compressor)
                && (!this.expression.is_call_pure(compressor)
                    || this.expression.has_side_effects(compressor))) {
                return true;
            }
            return any(this.args, compressor);
        });
        def(AST_Switch, function(compressor){
            return this.expression.has_side_effects(compressor)
                || any(this.body, compressor);
        });
        def(AST_Case, function(compressor){
            return this.expression.has_side_effects(compressor)
                || any(this.body, compressor);
        });
        def(AST_Try, function(compressor){
            return any(this.body, compressor)
                || this.bcatch && this.bcatch.has_side_effects(compressor)
                || this.bfinally && this.bfinally.has_side_effects(compressor);
        });
        def(AST_If, function(compressor){
            return this.condition.has_side_effects(compressor)
                || this.body && this.body.has_side_effects(compressor)
                || this.alternative && this.alternative.has_side_effects(compressor);
        });
        def(AST_LabeledStatement, function(compressor){
            return this.body.has_side_effects(compressor);
        });
        def(AST_SimpleStatement, function(compressor){
            return this.body.has_side_effects(compressor);
        });
        def(AST_Lambda, return_false);
        def(AST_Class, return_false);
        def(AST_DefClass, return_true);
        def(AST_Binary, function(compressor){
            return this.left.has_side_effects(compressor)
                || this.right.has_side_effects(compressor);
        });
        def(AST_Assign, return_true);
        def(AST_Conditional, function(compressor){
            return this.condition.has_side_effects(compressor)
                || this.consequent.has_side_effects(compressor)
                || this.alternative.has_side_effects(compressor);
        });
        def(AST_Unary, function(compressor){
            return unary_side_effects(this.operator)
                || this.expression.has_side_effects(compressor);
        });
        def(AST_SymbolRef, function(compressor){
            return !this.is_declared(compressor);
        });
        def(AST_SymbolDeclaration, return_false);
        def(AST_Object, function(compressor){
            return any(this.properties, compressor);
        });
        def(AST_ObjectProperty, function(compressor){
            if (this.key instanceof AST_ObjectKeyVal &&
                    this.key.has_side_effects(compressor))
                return true;
            return this.value.has_side_effects(compressor);
        });
        def(AST_Array, function(compressor){
            return any(this.elements, compressor);
        });
        def(AST_Dot, function(compressor){
            return this.expression.may_throw_on_access(compressor)
                || this.expression.has_side_effects(compressor);
        });
        def(AST_Sub, function(compressor){
            return this.expression.may_throw_on_access(compressor)
                || this.expression.has_side_effects(compressor)
                || this.property.has_side_effects(compressor);
        });
        def(AST_Sequence, function(compressor){
            return any(this.expressions, compressor);
        });
        def(AST_Definitions, function(compressor){
            return any(this.definitions, compressor);
        });
        def(AST_VarDef, function(compressor){
            return this.value;
        });
        def(AST_TemplateSegment, return_false);
        def(AST_TemplateString, function(compressor){
            return any(this.segments, compressor);
        });
    })(function(node, func){
        node.DEFMETHOD("has_side_effects", func);
    });

    // determine if expression may throw
    (function(def){
        def(AST_Node, return_true);

        def(AST_Class, return_false);
        def(AST_Constant, return_false);
        def(AST_EmptyStatement, return_false);
        def(AST_Lambda, return_false);
        def(AST_SymbolDeclaration, return_false);
        def(AST_This, return_false);

        function any(list, compressor) {
            for (var i = list.length; --i >= 0;)
                if (list[i].may_throw(compressor))
                    return true;
            return false;
        }

        def(AST_Array, function(compressor){
            return any(this.elements, compressor);
        });
        def(AST_Assign, function(compressor){
            if (this.right.may_throw(compressor)) return true;
            if (!compressor.has_directive("use strict")
                && this.operator == "="
                && this.left instanceof AST_SymbolRef) {
                return false;
            }
            return this.left.may_throw(compressor);
        });
        def(AST_Binary, function(compressor){
            return this.left.may_throw(compressor)
                || this.right.may_throw(compressor);
        });
        def(AST_Block, function(compressor){
            return any(this.body, compressor);
        });
        def(AST_Call, function(compressor){
            if (any(this.args, compressor)) return true;
            if (this.is_expr_pure(compressor)) return false;
            if (this.expression.may_throw(compressor)) return true;
            return !(this.expression instanceof AST_Lambda)
                || any(this.expression.body, compressor);
        });
        def(AST_Case, function(compressor){
            return this.expression.may_throw(compressor)
                || any(this.body, compressor);
        });
        def(AST_Conditional, function(compressor){
            return this.condition.may_throw(compressor)
                || this.consequent.may_throw(compressor)
                || this.alternative.may_throw(compressor);
        });
        def(AST_Definitions, function(compressor){
            return any(this.definitions, compressor);
        });
        def(AST_Dot, function(compressor){
            return this.expression.may_throw_on_access(compressor)
                || this.expression.may_throw(compressor);
        });
        def(AST_If, function(compressor){
            return this.condition.may_throw(compressor)
                || this.body && this.body.may_throw(compressor)
                || this.alternative && this.alternative.may_throw(compressor);
        });
        def(AST_LabeledStatement, function(compressor){
            return this.body.may_throw(compressor);
        });
        def(AST_Object, function(compressor){
            return any(this.properties, compressor);
        });
        def(AST_ObjectProperty, function(compressor){
            return this.value.may_throw(compressor);
        });
        def(AST_Sequence, function(compressor){
            return any(this.expressions, compressor);
        });
        def(AST_SimpleStatement, function(compressor){
            return this.body.may_throw(compressor);
        });
        def(AST_Sub, function(compressor){
            return this.expression.may_throw_on_access(compressor)
                || this.expression.may_throw(compressor)
                || this.property.may_throw(compressor);
        });
        def(AST_Switch, function(compressor){
            return this.expression.may_throw(compressor)
                || any(this.body, compressor);
        });
        def(AST_SymbolRef, function(compressor){
            return !this.is_declared(compressor);
        });
        def(AST_Try, function(compressor){
            return any(this.body, compressor)
                || this.bcatch && this.bcatch.may_throw(compressor)
                || this.bfinally && this.bfinally.may_throw(compressor);
        });
        def(AST_Unary, function(compressor){
            if (this.operator == "typeof" && this.expression instanceof AST_SymbolRef)
                return false;
            return this.expression.may_throw(compressor);
        });
        def(AST_VarDef, function(compressor){
            if (!this.value) return false;
            return this.value.may_throw(compressor);
        });
    })(function(node, func){
        node.DEFMETHOD("may_throw", func);
    });

    // determine if expression is constant
    (function(def){
        function all(list) {
            for (var i = list.length; --i >= 0;)
                if (!list[i].is_constant_expression())
                    return false;
            return true;
        }

        function all_refs_local(scope) {
            var self = this;
            var result = true;
            self.walk(new TreeWalker(function(node) {
                if (!result) return true;
                if (node instanceof AST_SymbolRef) {
                    if (self.inlined) {
                        result = false;
                        return true;
                    }
                    var def = node.definition();
                    if (member(def, self.enclosed)
                        && !self.variables.has(def.name)) {
                        if (scope) {
                            var scope_def = scope.find_variable(node);
                            if (def.undeclared ? !scope_def : scope_def === def) {
                                result = "f";
                                return true;
                            }
                        }
                        result = false;
                    }
                    return true;
                }
                if (node instanceof AST_This && self instanceof AST_Arrow) {
                    result = false;
                    return true;
                }
            }));
            return result;
        }

        def(AST_Node, return_false);
        def(AST_Constant, return_true);
        def(AST_Class, all_refs_local);
        def(AST_Lambda, all_refs_local);
        def(AST_Unary, function(){
            return this.expression.is_constant_expression();
        });
        def(AST_Binary, function(){
            return this.left.is_constant_expression() && this.right.is_constant_expression();
        });
        def(AST_Array, function(){
            return all(this.elements);
        });
        def(AST_Object, function(){
            return all(this.properties);
        });
        def(AST_ObjectProperty, function(){
            return !(this.key instanceof AST_Node) && this.value.is_constant_expression();
        });
    })(function(node, func){
        node.DEFMETHOD("is_constant_expression", func);
    });

    // tell me if a statement aborts
    function aborts(thing) {
        return thing && thing.aborts();
    };
    (function(def){
        def(AST_Statement, return_null);
        def(AST_Jump, return_this);
        function block_aborts(){
            var n = this.body.length;
            return n > 0 && aborts(this.body[n - 1]);
        };
        def(AST_Import, function(){ return null; });
        def(AST_BlockStatement, block_aborts);
        def(AST_SwitchBranch, block_aborts);
        def(AST_If, function(){
            return this.alternative && aborts(this.body) && aborts(this.alternative) && this;
        });
    })(function(node, func){
        node.DEFMETHOD("aborts", func);
    });

    /* -----[ optimizers ]----- */

    OPT(AST_Directive, function(self, compressor){
        if (compressor.has_directive(self.value) !== self) {
            return make_node(AST_EmptyStatement, self);
        }
        return self;
    });

    OPT(AST_Debugger, function(self, compressor){
        if (compressor.option("drop_debugger"))
            return make_node(AST_EmptyStatement, self);
        return self;
    });

    OPT(AST_LabeledStatement, function(self, compressor){
        if (self.body instanceof AST_Break
            && compressor.loopcontrol_target(self.body) === self.body) {
            return make_node(AST_EmptyStatement, self);
        }
        return self.label.references.length == 0 ? self.body : self;
    });

    OPT(AST_Block, function(self, compressor){
        tighten_body(self.body, compressor);
        return self;
    });

    OPT(AST_BlockStatement, function(self, compressor){
        tighten_body(self.body, compressor);
        switch (self.body.length) {
          case 1:
            if (!compressor.has_directive("use strict") && compressor.parent() instanceof AST_If
                || can_be_evicted_from_block(self.body[0])) {
                return self.body[0];
            }
            break;
          case 0: return make_node(AST_EmptyStatement, self);
        }
        return self;
    });

    AST_Scope.DEFMETHOD("drop_unused", function(compressor){
        if (!compressor.option("unused")) return;
        if (compressor.has_directive("use asm")) return;
        var self = this;
        if (self.uses_eval || self.uses_with) return;
        var drop_funcs = !(self instanceof AST_Toplevel) || compressor.toplevel.funcs;
        var drop_vars = !(self instanceof AST_Toplevel) || compressor.toplevel.vars;
        var assign_as_unused = /keep_assign/.test(compressor.option("unused")) ? return_false : function(node) {
            if (node instanceof AST_Assign && (node.write_only || node.operator == "=")) {
                return node.left;
            }
            if (node instanceof AST_Unary && node.write_only) return node.expression;
        };
        var in_use = [];
        var in_use_ids = Object.create(null); // avoid expensive linear scans of in_use
        var fixed_ids = Object.create(null);
        if (self instanceof AST_Toplevel && compressor.top_retain) {
            self.variables.each(function(def) {
                if (compressor.top_retain(def) && !(def.id in in_use_ids)) {
                    in_use_ids[def.id] = true;
                    in_use.push(def);
                }
            });
        }
        var var_defs_by_id = new Dictionary();
        var initializations = new Dictionary();
        var destructuring_value = null;
        // pass 1: find out which symbols are directly used in
        // this scope (not in nested scopes).
        var scope = this;
        var tw = new TreeWalker(function(node, descend){
            if (node === self) return;
            if (node instanceof AST_Defun || node instanceof AST_DefClass) {
                var node_def = node.name.definition();
                var in_export = tw.parent() instanceof AST_Export;
                if (in_export || !drop_funcs && scope === self) {
                    if (node_def.global && !(node_def.id in in_use_ids)) {
                        in_use_ids[node_def.id] = true;
                        in_use.push(node_def);
                    }
                }
                initializations.add(node_def.id, node);
                return true; // don't go in nested scopes
            }
            if (node instanceof AST_SymbolFunarg && scope === self) {
                var_defs_by_id.add(node.definition().id, node);
            }
            if (node instanceof AST_Definitions && scope === self) {
                var in_export = tw.parent() instanceof AST_Export;
                node.definitions.forEach(function(def){
                    if (def.name instanceof AST_SymbolVar) {
                        var_defs_by_id.add(def.name.definition().id, def);
                    }
                    if (in_export || !drop_vars) {
                        def.name.walk(new TreeWalker(function(node) {
                            if (node instanceof AST_SymbolDeclaration) {
                                var def = node.definition();
                                if ((in_export || def.global) && !(def.id in in_use_ids)) {
                                    in_use_ids[def.id] = true;
                                    in_use.push(def);
                                }
                            }
                        }));
                    }
                    if (def.value) {
                        if (def.name instanceof AST_Destructuring) {
                            var destructuring_cache = destructuring_value;
                            destructuring_value = def.value;
                            def.walk(tw);
                            destructuring_value = destructuring_cache;
                        } else {
                            var node_def = def.name.definition();;
                            initializations.add(node_def.id, def.value);
                            if (!node_def.chained && def.name.fixed_value() === def.value) {
                                fixed_ids[node_def.id] = def;
                            }
                        }
                        if (def.value.has_side_effects(compressor)) {
                            def.value.walk(tw);
                        }
                    }
                });
                return true;
            }
            if (node.destructuring && destructuring_value) {
                initializations.add(node.name, destructuring_value);
            }
            return scan_ref_scoped(node, descend);
        });
        self.walk(tw);
        // pass 2: for every used symbol we need to walk its
        // initialization code to figure out if it uses other
        // symbols (that may not be in_use).
        tw = new TreeWalker(scan_ref_scoped);
        for (var i = 0; i < in_use.length; i++) {
            var init = initializations.get(in_use[i].id);
            if (init) init.forEach(function(init) {
                init.walk(tw);
            });
        }
        // pass 3: we should drop declarations not in_use
        var tt = new TreeTransformer(
            function before(node, descend, in_list) {
                var parent = tt.parent();
                if (drop_vars) {
                    var sym = assign_as_unused(node);
                    if (sym instanceof AST_SymbolRef) {
                        var def = sym.definition();
                        var in_use = def.id in in_use_ids;
                        if (node instanceof AST_Assign) {
                            if (!in_use || def.id in fixed_ids && fixed_ids[def.id] !== node) {
                                return maintain_this_binding(parent, node, node.right.transform(tt));
                            }
                        } else if (!in_use) return make_node(AST_Number, node, {
                            value: 0
                        });
                    }
                }
                if (scope !== self) return;
                if (node.name
                    && (!compressor.option("keep_classnames") && node instanceof AST_ClassExpression
                        || !compressor.option("keep_fnames") && node instanceof AST_Function)) {
                    var def = node.name.definition();
                    // any declarations with same name will overshadow
                    // name of this anonymous function and can therefore
                    // never be used anywhere
                    if (!(def.id in in_use_ids) || def.orig.length > 1)
                        node.name = null;
                }
                if (node instanceof AST_Lambda && !(node instanceof AST_Accessor)) {
                    var trim = !compressor.option("keep_fargs");
                    for (var a = node.argnames, i = a.length; --i >= 0;) {
                        var sym = a[i];
                        if (sym instanceof AST_Expansion) {
                            sym = sym.expression;
                        }
                        if (sym instanceof AST_DefaultAssign) {
                            sym = sym.left;
                        }
                        // Do not drop destructuring arguments.
                        // They constitute a type assertion, so dropping
                        // them would stop that TypeError which would happen
                        // if someone called it with an incorrectly formatted
                        // parameter.
                        if (!(sym instanceof AST_Destructuring) && !(sym.definition().id in in_use_ids)) {
                            sym.__unused = true;
                            if (trim) {
                                a.pop();
                                compressor[sym.unreferenced() ? "warn" : "info"]("Dropping unused function argument {name} [{file}:{line},{col}]", template(sym));
                            }
                        }
                        else {
                            trim = false;
                        }
                    }
                }
                if ((node instanceof AST_Defun || node instanceof AST_DefClass) && node !== self) {
                    var def = node.name.definition();
                    var keep = (def.id in in_use_ids) || !drop_funcs && def.global;
                    if (!keep) {
                        compressor[node.name.unreferenced() ? "warn" : "info"]("Dropping unused function {name} [{file}:{line},{col}]", template(node.name));
                        def.eliminated++;
                        return make_node(AST_EmptyStatement, node);
                    }
                }
                if (node instanceof AST_Definitions && !(parent instanceof AST_ForIn && parent.init === node)) {
                    var drop_block = !(parent instanceof AST_Toplevel) && !(node instanceof AST_Var);
                    // place uninitialized names at the start
                    var body = [], head = [], tail = [];
                    // for unused names whose initialization has
                    // side effects, we can cascade the init. code
                    // into the next one, or next statement.
                    var side_effects = [];
                    node.definitions.forEach(function(def) {
                        if (def.value) def.value = def.value.transform(tt);
                        if (def.name instanceof AST_Destructuring) return tail.push(def);
                        var sym = def.name.definition();
                        if (drop_block && sym.global) return tail.push(def);
                        if (!(drop_vars || drop_block) || sym.id in in_use_ids) {
                            if (def.value && sym.id in fixed_ids && fixed_ids[sym.id] !== def) {
                                def.value = def.value.drop_side_effect_free(compressor);
                            }
                            if (def.name instanceof AST_SymbolVar) {
                                var var_defs = var_defs_by_id.get(sym.id);
                                if (var_defs.length > 1 && (!def.value || sym.orig.indexOf(def.name) > sym.eliminated)) {
                                    compressor.warn("Dropping duplicated definition of variable {name} [{file}:{line},{col}]", template(def.name));
                                    if (def.value) {
                                        var ref = make_node(AST_SymbolRef, def.name, def.name);
                                        sym.references.push(ref);
                                        var assign = make_node(AST_Assign, def, {
                                            operator: "=",
                                            left: ref,
                                            right: def.value
                                        });
                                        if (fixed_ids[sym.id] === def) {
                                            fixed_ids[sym.id] = assign;
                                        }
                                        side_effects.push(assign.transform(tt));
                                    }
                                    remove(var_defs, def);
                                    sym.eliminated++;
                                    return;
                                }
                            }
                            if (def.value) {
                                if (side_effects.length > 0) {
                                    if (tail.length > 0) {
                                        side_effects.push(def.value);
                                        def.value = make_sequence(def.value, side_effects);
                                    } else {
                                        body.push(make_node(AST_SimpleStatement, node, {
                                            body: make_sequence(node, side_effects)
                                        }));
                                    }
                                    side_effects = [];
                                }
                                tail.push(def);
                            } else {
                                head.push(def);
                            }
                        } else if (sym.orig[0] instanceof AST_SymbolCatch) {
                            var value = def.value && def.value.drop_side_effect_free(compressor);
                            if (value) side_effects.push(value);
                            def.value = null;
                            head.push(def);
                        } else {
                            var value = def.value && def.value.drop_side_effect_free(compressor);
                            if (value) {
                                compressor.warn("Side effects in initialization of unused variable {name} [{file}:{line},{col}]", template(def.name));
                                side_effects.push(value);
                            } else {
                                compressor[def.name.unreferenced() ? "warn" : "info"]("Dropping unused variable {name} [{file}:{line},{col}]", template(def.name));
                            }
                            sym.eliminated++;
                        }
                    });
                    if (head.length > 0 || tail.length > 0) {
                        node.definitions = head.concat(tail);
                        body.push(node);
                    }
                    if (side_effects.length > 0) {
                        body.push(make_node(AST_SimpleStatement, node, {
                            body: make_sequence(node, side_effects)
                        }));
                    }
                    switch (body.length) {
                      case 0:
                        return in_list ? MAP.skip : make_node(AST_EmptyStatement, node);
                      case 1:
                        return body[0];
                      default:
                        return in_list ? MAP.splice(body) : make_node(AST_BlockStatement, node, {
                            body: body
                        });
                    }
                }
                // certain combination of unused name + side effect leads to:
                //    https://github.com/mishoo/UglifyJS2/issues/44
                //    https://github.com/mishoo/UglifyJS2/issues/1830
                //    https://github.com/mishoo/UglifyJS2/issues/1838
                // that's an invalid AST.
                // We fix it at this stage by moving the `var` outside the `for`.
                if (node instanceof AST_For) {
                    descend(node, this);
                    var block;
                    if (node.init instanceof AST_BlockStatement) {
                        block = node.init;
                        node.init = block.body.pop();
                        block.body.push(node);
                    }
                    if (node.init instanceof AST_SimpleStatement) {
                        node.init = node.init.body;
                    } else if (is_empty(node.init)) {
                        node.init = null;
                    }
                    return !block ? node : in_list ? MAP.splice(block.body) : block;
                }
                if (node instanceof AST_LabeledStatement && node.body instanceof AST_For) {
                    descend(node, this);
                    if (node.body instanceof AST_BlockStatement) {
                        var block = node.body;
                        node.body = block.body.pop();
                        block.body.push(node);
                        return in_list ? MAP.splice(block.body) : block;
                    }
                    return node;
                }
                if (node instanceof AST_BlockStatement) {
                    descend(node, this);
                    if (in_list && all(node.body, can_be_evicted_from_block)) {
                        return MAP.splice(node.body);
                    }
                    return node;
                }
                if (node instanceof AST_Scope) {
                    var save_scope = scope;
                    scope = node;
                    descend(node, this);
                    scope = save_scope;
                    return node;
                }

                function template(sym) {
                    return {
                        name : sym.name,
                        file : sym.start.file,
                        line : sym.start.line,
                        col  : sym.start.col
                    };
                }
            }
        );
        self.transform(tt);

        function scan_ref_scoped(node, descend) {
            var node_def, sym = assign_as_unused(node);
            if (sym instanceof AST_SymbolRef
                && !is_ref_of(node.left, AST_SymbolBlockDeclaration)
                && self.variables.get(sym.name) === (node_def = sym.definition())) {
                if (node instanceof AST_Assign) {
                    node.right.walk(tw);
                    if (!node_def.chained && node.left.fixed_value() === node.right) {
                        fixed_ids[node_def.id] = node;
                    }
                }
                return true;
            }
            if (node instanceof AST_SymbolRef) {
                node_def = node.definition();
                if (!(node_def.id in in_use_ids)) {
                    in_use_ids[node_def.id] = true;
                    in_use.push(node_def);
                    if (node_def = node_def.redefined()) {
                        in_use_ids[node_def.id] = true;
                        in_use.push(node_def);
                    }
                }
                return true;
            }
            if (node instanceof AST_Scope) {
                var save_scope = scope;
                scope = node;
                descend();
                scope = save_scope;
                return true;
            }
        }
    });

    AST_Scope.DEFMETHOD("hoist_declarations", function(compressor){
        var self = this;
        if (compressor.has_directive("use asm")) return self;
        // Hoisting makes no sense in an arrow func
        if (!Array.isArray(self.body)) return self;

        var hoist_funs = compressor.option("hoist_funs");
        var hoist_vars = compressor.option("hoist_vars");

        if (hoist_funs || hoist_vars) {
            var dirs = [];
            var hoisted = [];
            var vars = new Dictionary(), vars_found = 0, var_decl = 0;
            // let's count var_decl first, we seem to waste a lot of
            // space if we hoist `var` when there's only one.
            self.walk(new TreeWalker(function(node){
                if (node instanceof AST_Scope && node !== self)
                    return true;
                if (node instanceof AST_Var) {
                    ++var_decl;
                    return true;
                }
            }));
            hoist_vars = hoist_vars && var_decl > 1;
            var tt = new TreeTransformer(
                function before(node) {
                    if (node !== self) {
                        if (node instanceof AST_Directive) {
                            dirs.push(node);
                            return make_node(AST_EmptyStatement, node);
                        }
                        if (hoist_funs && node instanceof AST_Defun
                            && !(tt.parent() instanceof AST_Export)
                            && tt.parent() === self) {
                            hoisted.push(node);
                            return make_node(AST_EmptyStatement, node);
                        }
                        if (hoist_vars && node instanceof AST_Var) {
                            node.definitions.forEach(function(def){
                                if (def.name instanceof AST_Destructuring) return;
                                vars.set(def.name.name, def);
                                ++vars_found;
                            });
                            var seq = node.to_assignments(compressor);
                            var p = tt.parent();
                            if (p instanceof AST_ForIn && p.init === node) {
                                if (seq == null) {
                                    var def = node.definitions[0].name;
                                    return make_node(AST_SymbolRef, def, def);
                                }
                                return seq;
                            }
                            if (p instanceof AST_For && p.init === node) {
                                return seq;
                            }
                            if (!seq) return make_node(AST_EmptyStatement, node);
                            return make_node(AST_SimpleStatement, node, {
                                body: seq
                            });
                        }
                        if (node instanceof AST_Scope)
                            return node; // to avoid descending in nested scopes
                    }
                }
            );
            self = self.transform(tt);
            if (vars_found > 0) {
                // collect only vars which don't show up in self's arguments list
                var defs = [];
                vars.each(function(def, name){
                    if (self instanceof AST_Lambda
                        && find_if(function(x){ return x.name == def.name.name },
                                   self.args_as_names())) {
                        vars.del(name);
                    } else {
                        def = def.clone();
                        def.value = null;
                        defs.push(def);
                        vars.set(name, def);
                    }
                });
                if (defs.length > 0) {
                    // try to merge in assignments
                    for (var i = 0; i < self.body.length;) {
                        if (self.body[i] instanceof AST_SimpleStatement) {
                            var expr = self.body[i].body, sym, assign;
                            if (expr instanceof AST_Assign
                                && expr.operator == "="
                                && (sym = expr.left) instanceof AST_Symbol
                                && vars.has(sym.name))
                            {
                                var def = vars.get(sym.name);
                                if (def.value) break;
                                def.value = expr.right;
                                remove(defs, def);
                                defs.push(def);
                                self.body.splice(i, 1);
                                continue;
                            }
                            if (expr instanceof AST_Sequence
                                && (assign = expr.expressions[0]) instanceof AST_Assign
                                && assign.operator == "="
                                && (sym = assign.left) instanceof AST_Symbol
                                && vars.has(sym.name))
                            {
                                var def = vars.get(sym.name);
                                if (def.value) break;
                                def.value = assign.right;
                                remove(defs, def);
                                defs.push(def);
                                self.body[i].body = make_sequence(expr, expr.expressions.slice(1));
                                continue;
                            }
                        }
                        if (self.body[i] instanceof AST_EmptyStatement) {
                            self.body.splice(i, 1);
                            continue;
                        }
                        if (self.body[i] instanceof AST_BlockStatement) {
                            var tmp = [ i, 1 ].concat(self.body[i].body);
                            self.body.splice.apply(self.body, tmp);
                            continue;
                        }
                        break;
                    }
                    defs = make_node(AST_Var, self, {
                        definitions: defs
                    });
                    hoisted.push(defs);
                };
            }
            self.body = dirs.concat(hoisted, self.body);
        }
        return self;
    });

    AST_Scope.DEFMETHOD("var_names", function() {
        var var_names = this._var_names;
        if (!var_names) {
            this._var_names = var_names = Object.create(null);
            this.enclosed.forEach(function(def) {
                var_names[def.name] = true;
            });
            this.variables.each(function(def, name) {
                var_names[name] = true;
            });
        }
        return var_names;
    });

    AST_Scope.DEFMETHOD("make_var_name", function(prefix) {
        var var_names = this.var_names();
        prefix = prefix.replace(/[^a-z_$]+/ig, "_");
        var name = prefix;
        for (var i = 0; var_names[name]; i++) name = prefix + "$" + i;
        var_names[name] = true;
        return name;
    });

    AST_Scope.DEFMETHOD("hoist_properties", function(compressor){
        var self = this;
        if (!compressor.option("hoist_props") || compressor.has_directive("use asm")) return self;
        var top_retain = self instanceof AST_Toplevel && compressor.top_retain || return_false;
        var defs_by_id = Object.create(null);
        var tt = new TreeTransformer(function(node, descend) {
            if (node instanceof AST_Definitions && tt.parent() instanceof AST_Export) return node;
            if (node instanceof AST_VarDef) {
                var sym = node.name, def, value;
                if (sym.scope === self
                    && (def = sym.definition()).escaped != 1
                    && !def.single_use
                    && !def.direct_access
                    && !compressor.exposed(def)
                    && !top_retain(def)
                    && (value = sym.fixed_value()) === node.value
                    && value instanceof AST_Object) {
                    descend(node, this);
                    var defs = new Dictionary();
                    var assignments = [];
                    value.properties.forEach(function(prop) {
                        assignments.push(make_node(AST_VarDef, node, {
                            name: make_sym(prop.key),
                            value: prop.value
                        }));
                    });
                    defs_by_id[def.id] = defs;
                    return MAP.splice(assignments);
                }
            }
            if (node instanceof AST_PropAccess && node.expression instanceof AST_SymbolRef) {
                var defs = defs_by_id[node.expression.definition().id];
                if (defs) {
                    var def = defs.get(get_value(node.property));
                    var sym = make_node(AST_SymbolRef, node, {
                        name: def.name,
                        scope: node.expression.scope,
                        thedef: def
                    });
                    sym.reference({});
                    return sym;
                }
            }

            function make_sym(key) {
                var new_var = make_node(sym.CTOR, sym, {
                    name: self.make_var_name(sym.name + "_" + key),
                    scope: self
                });
                var def = self.def_variable(new_var);
                defs.set(key, def);
                self.enclosed.push(def);
                return new_var;
            }
        });
        return self.transform(tt);
    });

    // drop_side_effect_free()
    // remove side-effect-free parts which only affects return value
    (function(def){
        // Drop side-effect-free elements from an array of expressions.
        // Returns an array of expressions with side-effects or null
        // if all elements were dropped. Note: original array may be
        // returned if nothing changed.
        function trim(nodes, compressor, first_in_statement) {
            var len = nodes.length;
            if (!len) return null;
            var ret = [], changed = false;
            for (var i = 0; i < len; i++) {
                var node = nodes[i].drop_side_effect_free(compressor, first_in_statement);
                changed |= node !== nodes[i];
                if (node) {
                    ret.push(node);
                    first_in_statement = false;
                }
            }
            return changed ? ret.length ? ret : null : nodes;
        }

        def(AST_Node, return_this);
        def(AST_Constant, return_null);
        def(AST_This, return_null);
        def(AST_Call, function(compressor, first_in_statement){
            if (!this.is_expr_pure(compressor)) {
                if (this.expression.is_call_pure(compressor)) {
                    var exprs = this.args.slice();
                    exprs.unshift(this.expression.expression);
                    exprs = trim(exprs, compressor, first_in_statement);
                    return exprs && make_sequence(this, exprs);
                }
                if (is_func_expr(this.expression)
                    && (!this.expression.name || !this.expression.name.definition().references.length)) {
                    var node = this.clone();
                    node.expression.process_expression(false, compressor);
                    return node;
                }
                return this;
            }
            if (this.pure) {
                compressor.warn("Dropping __PURE__ call [{file}:{line},{col}]", this.start);
            }
            var args = trim(this.args, compressor, first_in_statement);
            return args && make_sequence(this, args);
        });
        def(AST_Accessor, return_null);
        def(AST_Function, return_null);
        def(AST_Arrow, return_null);
        def(AST_ClassExpression, return_null);
        def(AST_Binary, function(compressor, first_in_statement){
            var right = this.right.drop_side_effect_free(compressor);
            if (!right) return this.left.drop_side_effect_free(compressor, first_in_statement);
            if (lazy_op(this.operator)) {
                if (right === this.right) return this;
                var node = this.clone();
                node.right = right;
                return node;
            } else {
                var left = this.left.drop_side_effect_free(compressor, first_in_statement);
                if (!left) return this.right.drop_side_effect_free(compressor, first_in_statement);
                return make_sequence(this, [ left, right ]);
            }
        });
        def(AST_Assign, function(compressor){
            var left = this.left;
            if (left.has_side_effects(compressor)
                || compressor.has_directive("use strict")
                    && left instanceof AST_PropAccess
                    && left.expression.is_constant()) {
                return this;
            }
            this.write_only = true;
            while (left instanceof AST_PropAccess) {
                left = left.expression;
            }
            if (left.is_constant_expression(compressor.find_parent(AST_Scope))) {
                return this.right.drop_side_effect_free(compressor);
            }
            return this;
        });
        def(AST_Conditional, function(compressor){
            var consequent = this.consequent.drop_side_effect_free(compressor);
            var alternative = this.alternative.drop_side_effect_free(compressor);
            if (consequent === this.consequent && alternative === this.alternative) return this;
            if (!consequent) return alternative ? make_node(AST_Binary, this, {
                operator: "||",
                left: this.condition,
                right: alternative
            }) : this.condition.drop_side_effect_free(compressor);
            if (!alternative) return make_node(AST_Binary, this, {
                operator: "&&",
                left: this.condition,
                right: consequent
            });
            var node = this.clone();
            node.consequent = consequent;
            node.alternative = alternative;
            return node;
        });
        def(AST_Unary, function(compressor, first_in_statement){
            if (unary_side_effects(this.operator)) {
                this.write_only = !this.expression.has_side_effects(compressor);
                return this;
            }
            if (this.operator == "typeof" && this.expression instanceof AST_SymbolRef) return null;
            var expression = this.expression.drop_side_effect_free(compressor, first_in_statement);
            if (first_in_statement && expression && is_iife_call(expression)) {
                if (expression === this.expression && this.operator == "!") return this;
                return expression.negate(compressor, first_in_statement);
            }
            return expression;
        });
        def(AST_SymbolRef, function(compressor) {
            return this.is_declared(compressor) ? null : this;
        });
        def(AST_Object, function(compressor, first_in_statement){
            var values = trim(this.properties, compressor, first_in_statement);
            return values && make_sequence(this, values);
        });
        def(AST_ObjectProperty, function(compressor, first_in_statement){
            return this.value.drop_side_effect_free(compressor, first_in_statement);
        });
        def(AST_Array, function(compressor, first_in_statement){
            var values = trim(this.elements, compressor, first_in_statement);
            return values && make_sequence(this, values);
        });
        def(AST_Dot, function(compressor, first_in_statement){
            if (this.expression.may_throw_on_access(compressor)) return this;
            return this.expression.drop_side_effect_free(compressor, first_in_statement);
        });
        def(AST_Sub, function(compressor, first_in_statement){
            if (this.expression.may_throw_on_access(compressor)) return this;
            var expression = this.expression.drop_side_effect_free(compressor, first_in_statement);
            if (!expression) return this.property.drop_side_effect_free(compressor, first_in_statement);
            var property = this.property.drop_side_effect_free(compressor);
            if (!property) return expression;
            return make_sequence(this, [ expression, property ]);
        });
        def(AST_Sequence, function(compressor){
            var last = this.tail_node();
            var expr = last.drop_side_effect_free(compressor);
            if (expr === last) return this;
            var expressions = this.expressions.slice(0, -1);
            if (expr) expressions.push(expr);
            return make_sequence(this, expressions);
        });
        def(AST_Expansion, function(compressor, first_in_statement){
            return this.expression.drop_side_effect_free(compressor, first_in_statement);
        });
        def(AST_TemplateSegment, return_null);
        def(AST_TemplateString, function(compressor){
            var values = trim(this.segments, compressor, first_in_statement);
            return values && make_sequence(this, values);
        });
    })(function(node, func){
        node.DEFMETHOD("drop_side_effect_free", func);
    });

    OPT(AST_SimpleStatement, function(self, compressor){
        if (compressor.option("side_effects")) {
            var body = self.body;
            var node = body.drop_side_effect_free(compressor, true);
            if (!node) {
                compressor.warn("Dropping side-effect-free statement [{file}:{line},{col}]", self.start);
                return make_node(AST_EmptyStatement, self);
            }
            if (node !== body) {
                return make_node(AST_SimpleStatement, self, { body: node });
            }
        }
        return self;
    });

    OPT(AST_While, function(self, compressor){
        return compressor.option("loops") ? make_node(AST_For, self, self).optimize(compressor) : self;
    });

    OPT(AST_Do, function(self, compressor){
        if (!compressor.option("loops")) return self;
        var cond = self.condition.tail_node().evaluate(compressor);
        if (!(cond instanceof AST_Node)) {
            if (cond) return make_node(AST_For, self, {
                body: make_node(AST_BlockStatement, self.body, {
                    body: [
                        self.body,
                        make_node(AST_SimpleStatement, self.condition, {
                            body: self.condition
                        })
                    ]
                })
            }).optimize(compressor);
            var has_loop_control = false;
            var tw = new TreeWalker(function(node) {
                if (node instanceof AST_Scope || has_loop_control) return true;
                if (node instanceof AST_LoopControl && tw.loopcontrol_target(node) === self)
                    return has_loop_control = true;
            });
            var parent = compressor.parent();
            (parent instanceof AST_LabeledStatement ? parent : self).walk(tw);
            if (!has_loop_control) return make_node(AST_BlockStatement, self.body, {
                body: [
                    self.body,
                    make_node(AST_SimpleStatement, self.condition, {
                        body: self.condition
                    })
                ]
            }).optimize(compressor);
        }
        return self;
    });

    function if_break_in_loop(self, compressor) {
        var first = self.body instanceof AST_BlockStatement ? self.body.body[0] : self.body;
        if (compressor.option("dead_code") && is_break(first)) {
            var body = [];
            if (self.init instanceof AST_Statement) {
                body.push(self.init);
            } else if (self.init) {
                body.push(make_node(AST_SimpleStatement, self.init, {
                    body: self.init
                }));
            }
            if (self.condition) {
                body.push(make_node(AST_SimpleStatement, self.condition, {
                    body: self.condition
                }));
            }
            extract_declarations_from_unreachable_code(compressor, self.body, body);
            return make_node(AST_BlockStatement, self, {
                body: body
            });
        }
        if (first instanceof AST_If) {
            if (is_break(first.body)) {
                if (self.condition) {
                    self.condition = make_node(AST_Binary, self.condition, {
                        left: self.condition,
                        operator: "&&",
                        right: first.condition.negate(compressor),
                    });
                } else {
                    self.condition = first.condition.negate(compressor);
                }
                drop_it(first.alternative);
            } else if (is_break(first.alternative)) {
                if (self.condition) {
                    self.condition = make_node(AST_Binary, self.condition, {
                        left: self.condition,
                        operator: "&&",
                        right: first.condition,
                    });
                } else {
                    self.condition = first.condition;
                }
                drop_it(first.body);
            }
        }
        return self;

        function is_break(node) {
            return node instanceof AST_Break
                && compressor.loopcontrol_target(node) === compressor.self();
        }

        function drop_it(rest) {
            rest = as_statement_array(rest);
            if (self.body instanceof AST_BlockStatement) {
                self.body = self.body.clone();
                self.body.body = rest.concat(self.body.body.slice(1));
                self.body = self.body.transform(compressor);
            } else {
                self.body = make_node(AST_BlockStatement, self.body, {
                    body: rest
                }).transform(compressor);
            }
            self = if_break_in_loop(self, compressor);
        }
    }

    OPT(AST_For, function(self, compressor){
        if (!compressor.option("loops")) return self;
        if (compressor.option("side_effects") && self.init) {
            self.init = self.init.drop_side_effect_free(compressor);
        }
        if (self.condition) {
            var cond = self.condition.evaluate(compressor);
            if (!(cond instanceof AST_Node)) {
                if (cond) self.condition = null;
                else if (!compressor.option("dead_code")) {
                    var orig = self.condition;
                    self.condition = make_node_from_constant(cond, self.condition);
                    self.condition = best_of_expression(self.condition.transform(compressor), orig);
                }
            }
            if (compressor.option("dead_code")) {
                if (cond instanceof AST_Node) cond = self.condition.tail_node().evaluate(compressor);
                if (!cond) {
                    var body = [];
                    extract_declarations_from_unreachable_code(compressor, self.body, body);
                    if (self.init instanceof AST_Statement) {
                        body.push(self.init);
                    } else if (self.init) {
                        body.push(make_node(AST_SimpleStatement, self.init, {
                            body: self.init
                        }));
                    }
                    body.push(make_node(AST_SimpleStatement, self.condition, {
                        body: self.condition
                    }));
                    return make_node(AST_BlockStatement, self, { body: body }).optimize(compressor);
                }
            }
        }
        return if_break_in_loop(self, compressor);
    });

    OPT(AST_If, function(self, compressor){
        if (is_empty(self.alternative)) self.alternative = null;

        if (!compressor.option("conditionals")) return self;
        // if condition can be statically determined, warn and drop
        // one of the blocks.  note, statically determined implies
        // “has no side effects”; also it doesn't work for cases like
        // `x && true`, though it probably should.
        var cond = self.condition.evaluate(compressor);
        if (!compressor.option("dead_code") && !(cond instanceof AST_Node)) {
            var orig = self.condition;
            self.condition = make_node_from_constant(cond, orig);
            self.condition = best_of_expression(self.condition.transform(compressor), orig);
        }
        if (compressor.option("dead_code")) {
            if (cond instanceof AST_Node) cond = self.condition.tail_node().evaluate(compressor);
            if (!cond) {
                compressor.warn("Condition always false [{file}:{line},{col}]", self.condition.start);
                var body = [];
                extract_declarations_from_unreachable_code(compressor, self.body, body);
                body.push(make_node(AST_SimpleStatement, self.condition, {
                    body: self.condition
                }));
                if (self.alternative) body.push(self.alternative);
                return make_node(AST_BlockStatement, self, { body: body }).optimize(compressor);
            } else if (!(cond instanceof AST_Node)) {
                compressor.warn("Condition always true [{file}:{line},{col}]", self.condition.start);
                var body = [];
                if (self.alternative) {
                    extract_declarations_from_unreachable_code(compressor, self.alternative, body);
                }
                body.push(make_node(AST_SimpleStatement, self.condition, {
                    body: self.condition
                }));
                body.push(self.body);
                return make_node(AST_BlockStatement, self, { body: body }).optimize(compressor);
            }
        }
        var negated = self.condition.negate(compressor);
        var self_condition_length = self.condition.print_to_string().length;
        var negated_length = negated.print_to_string().length;
        var negated_is_best = negated_length < self_condition_length;
        if (self.alternative && negated_is_best) {
            negated_is_best = false; // because we already do the switch here.
            // no need to swap values of self_condition_length and negated_length
            // here because they are only used in an equality comparison later on.
            self.condition = negated;
            var tmp = self.body;
            self.body = self.alternative || make_node(AST_EmptyStatement, self);
            self.alternative = tmp;
        }
        if (is_empty(self.body) && is_empty(self.alternative)) {
            return make_node(AST_SimpleStatement, self.condition, {
                body: self.condition.clone()
            }).optimize(compressor);
        }
        if (self.body instanceof AST_SimpleStatement
            && self.alternative instanceof AST_SimpleStatement) {
            return make_node(AST_SimpleStatement, self, {
                body: make_node(AST_Conditional, self, {
                    condition   : self.condition,
                    consequent  : self.body.body,
                    alternative : self.alternative.body
                })
            }).optimize(compressor);
        }
        if (is_empty(self.alternative) && self.body instanceof AST_SimpleStatement) {
            if (self_condition_length === negated_length && !negated_is_best
                && self.condition instanceof AST_Binary && self.condition.operator == "||") {
                // although the code length of self.condition and negated are the same,
                // negated does not require additional surrounding parentheses.
                // see https://github.com/mishoo/UglifyJS2/issues/979
                negated_is_best = true;
            }
            if (negated_is_best) return make_node(AST_SimpleStatement, self, {
                body: make_node(AST_Binary, self, {
                    operator : "||",
                    left     : negated,
                    right    : self.body.body
                })
            }).optimize(compressor);
            return make_node(AST_SimpleStatement, self, {
                body: make_node(AST_Binary, self, {
                    operator : "&&",
                    left     : self.condition,
                    right    : self.body.body
                })
            }).optimize(compressor);
        }
        if (self.body instanceof AST_EmptyStatement
            && self.alternative instanceof AST_SimpleStatement) {
            return make_node(AST_SimpleStatement, self, {
                body: make_node(AST_Binary, self, {
                    operator : "||",
                    left     : self.condition,
                    right    : self.alternative.body
                })
            }).optimize(compressor);
        }
        if (self.body instanceof AST_Exit
            && self.alternative instanceof AST_Exit
            && self.body.TYPE == self.alternative.TYPE) {
            return make_node(self.body.CTOR, self, {
                value: make_node(AST_Conditional, self, {
                    condition   : self.condition,
                    consequent  : self.body.value || make_node(AST_Undefined, self.body),
                    alternative : self.alternative.value || make_node(AST_Undefined, self.alternative)
                }).transform(compressor)
            }).optimize(compressor);
        }
        if (self.body instanceof AST_If
            && !self.body.alternative
            && !self.alternative) {
            self = make_node(AST_If, self, {
                condition: make_node(AST_Binary, self.condition, {
                    operator: "&&",
                    left: self.condition,
                    right: self.body.condition
                }),
                body: self.body.body,
                alternative: null
            });
        }
        if (aborts(self.body)) {
            if (self.alternative) {
                var alt = self.alternative;
                self.alternative = null;
                return make_node(AST_BlockStatement, self, {
                    body: [ self, alt ]
                }).optimize(compressor);
            }
        }
        if (aborts(self.alternative)) {
            var body = self.body;
            self.body = self.alternative;
            self.condition = negated_is_best ? negated : self.condition.negate(compressor);
            self.alternative = null;
            return make_node(AST_BlockStatement, self, {
                body: [ self, body ]
            }).optimize(compressor);
        }
        return self;
    });

    OPT(AST_Switch, function(self, compressor){
        if (!compressor.option("switches")) return self;
        var branch;
        var value = self.expression.evaluate(compressor);
        if (!(value instanceof AST_Node)) {
            var orig = self.expression;
            self.expression = make_node_from_constant(value, orig);
            self.expression = best_of_expression(self.expression.transform(compressor), orig);
        }
        if (!compressor.option("dead_code")) return self;
        if (value instanceof AST_Node) {
            value = self.expression.tail_node().evaluate(compressor);
        }
        var decl = [];
        var body = [];
        var default_branch;
        var exact_match;
        for (var i = 0, len = self.body.length; i < len && !exact_match; i++) {
            branch = self.body[i];
            if (branch instanceof AST_Default) {
                if (!default_branch) {
                    default_branch = branch;
                } else {
                    eliminate_branch(branch, body[body.length - 1]);
                }
            } else if (!(value instanceof AST_Node)) {
                var exp = branch.expression.evaluate(compressor);
                if (!(exp instanceof AST_Node) && exp !== value) {
                    eliminate_branch(branch, body[body.length - 1]);
                    continue;
                }
                if (exp instanceof AST_Node) exp = branch.expression.tail_node().evaluate(compressor);
                if (exp === value) {
                    exact_match = branch;
                    if (default_branch) {
                        var default_index = body.indexOf(default_branch);
                        body.splice(default_index, 1);
                        eliminate_branch(default_branch, body[default_index - 1]);
                        default_branch = null;
                    }
                }
            }
            if (aborts(branch)) {
                var prev = body[body.length - 1];
                if (aborts(prev) && prev.body.length == branch.body.length
                    && make_node(AST_BlockStatement, prev, prev).equivalent_to(make_node(AST_BlockStatement, branch, branch))) {
                    prev.body = [];
                }
            }
            body.push(branch);
        }
        while (i < len) eliminate_branch(self.body[i++], body[body.length - 1]);
        if (body.length > 0) {
            body[0].body = decl.concat(body[0].body);
        }
        self.body = body;
        while (branch = body[body.length - 1]) {
            var stat = branch.body[branch.body.length - 1];
            if (stat instanceof AST_Break && compressor.loopcontrol_target(stat) === self)
                branch.body.pop();
            if (branch.body.length || branch instanceof AST_Case
                && (default_branch || branch.expression.has_side_effects(compressor))) break;
            if (body.pop() === default_branch) default_branch = null;
        }
        if (body.length == 0) {
            return make_node(AST_BlockStatement, self, {
                body: decl.concat(make_node(AST_SimpleStatement, self.expression, {
                    body: self.expression
                }))
            }).optimize(compressor);
        }
        if (body.length == 1 && (body[0] === exact_match || body[0] === default_branch)) {
            var has_break = false;
            var tw = new TreeWalker(function(node) {
                if (has_break
                    || node instanceof AST_Lambda
                    || node instanceof AST_SimpleStatement) return true;
                if (node instanceof AST_Break && tw.loopcontrol_target(node) === self)
                    has_break = true;
            });
            self.walk(tw);
            if (!has_break) {
                var statements = body[0].body.slice();
                var exp = body[0].expression;
                if (exp) statements.unshift(make_node(AST_SimpleStatement, exp, {
                    body: exp
                }));
                statements.unshift(make_node(AST_SimpleStatement, self.expression, {
                    body:self.expression
                }));
                return make_node(AST_BlockStatement, self, {
                    body: statements
                }).optimize(compressor);
            }
        }
        return self;

        function eliminate_branch(branch, prev) {
            if (prev && !aborts(prev)) {
                prev.body = prev.body.concat(branch.body);
            } else {
                extract_declarations_from_unreachable_code(compressor, branch, decl);
            }
        }
    });

    OPT(AST_Try, function(self, compressor){
        tighten_body(self.body, compressor);
        if (self.bcatch && self.bfinally && all(self.bfinally.body, is_empty)) self.bfinally = null;
        if (compressor.option("dead_code") && all(self.body, is_empty)) {
            var body = [];
            if (self.bcatch) {
                extract_declarations_from_unreachable_code(compressor, self.bcatch, body);
                body.forEach(function(stat) {
                    if (!(stat instanceof AST_Definitions)) return;
                    stat.definitions.forEach(function(var_def) {
                        var def = var_def.name.definition().redefined();
                        if (!def) return;
                        var_def.name = var_def.name.clone();
                        var_def.name.thedef = def;
                    });
                });
            }
            if (self.bfinally) body = body.concat(self.bfinally.body);
            return make_node(AST_BlockStatement, self, {
                body: body
            }).optimize(compressor);
        }
        return self;
    });

    AST_Definitions.DEFMETHOD("remove_initializers", function(){
        var decls = [];
        this.definitions.forEach(function(def) {
            if (def.name instanceof AST_SymbolDeclaration) {
                def.value = null;
                decls.push(def);
            } else def.name.walk(new TreeWalker(function(node) {
                if (node instanceof AST_SymbolDeclaration) {
                    decls.push(make_node(AST_VarDef, def, {
                        name: node,
                        value: null
                    }));
                }
            }));
        });
        this.definitions = decls;
    });

    AST_Definitions.DEFMETHOD("to_assignments", function(compressor){
        var reduce_vars = compressor.option("reduce_vars");
        var assignments = this.definitions.reduce(function(a, def){
            if (def.value && !(def.name instanceof AST_Destructuring)) {
                var name = make_node(AST_SymbolRef, def.name, def.name);
                a.push(make_node(AST_Assign, def, {
                    operator : "=",
                    left     : name,
                    right    : def.value
                }));
                if (reduce_vars) name.definition().fixed = false;
            } else if (def.value) {
                // Because it's a destructuring, do not turn into an assignment.
                var varDef = make_node(AST_VarDef, def, {
                    name: def.name,
                    value: def.value
                });
                var var_ = make_node(AST_Var, def, {
                    definitions: [ varDef ]
                });
                a.push(var_);
            }
            def = def.name.definition();
            def.eliminated++;
            def.replaced--;
            return a;
        }, []);
        if (assignments.length == 0) return null;
        return make_sequence(this, assignments);
    });

    OPT(AST_Definitions, function(self, compressor){
        if (self.definitions.length == 0)
            return make_node(AST_EmptyStatement, self);
        return self;
    });

    OPT(AST_Import, function(self, compressor) {
        return self;
    });

    OPT(AST_Call, function(self, compressor){
        var exp = self.expression;
        var fn = exp;
        var simple_args = all(self.args, function(arg) {
            return !(arg instanceof AST_Expansion);
        });
        if (compressor.option("reduce_vars") && fn instanceof AST_SymbolRef) {
            fn = fn.fixed_value();
        }
        var is_func = fn instanceof AST_Lambda;
        if (compressor.option("unused")
            && simple_args
            && is_func
            && !fn.uses_arguments
            && !fn.uses_eval) {
            var pos = 0, last = 0;
            for (var i = 0, len = self.args.length; i < len; i++) {
                if (fn.argnames[i] instanceof AST_Expansion) {
                    if (fn.argnames[i].expression.__unused) while (i < len) {
                        var node = self.args[i++].drop_side_effect_free(compressor);
                        if (node) {
                            self.args[pos++] = node;
                        }
                    } else while (i < len) {
                        self.args[pos++] = self.args[i++];
                    }
                    last = pos;
                    break;
                }
                var trim = i >= fn.argnames.length;
                if (trim || fn.argnames[i].__unused) {
                    var node = self.args[i].drop_side_effect_free(compressor);
                    if (node) {
                        self.args[pos++] = node;
                    } else if (!trim) {
                        self.args[pos++] = make_node(AST_Number, self.args[i], {
                            value: 0
                        });
                        continue;
                    }
                } else {
                    self.args[pos++] = self.args[i];
                }
                last = pos;
            }
            self.args.length = last;
        }
        if (compressor.option("unsafe")) {
            if (is_undeclared_ref(exp)) switch (exp.name) {
              case "Array":
                if (self.args.length != 1) {
                    return make_node(AST_Array, self, {
                        elements: self.args
                    }).optimize(compressor);
                }
                break;
              case "Object":
                if (self.args.length == 0) {
                    return make_node(AST_Object, self, {
                        properties: []
                    });
                }
                break;
              case "String":
                if (self.args.length == 0) return make_node(AST_String, self, {
                    value: ""
                });
                if (self.args.length <= 1) return make_node(AST_Binary, self, {
                    left: self.args[0],
                    operator: "+",
                    right: make_node(AST_String, self, { value: "" })
                }).optimize(compressor);
                break;
              case "Number":
                if (self.args.length == 0) return make_node(AST_Number, self, {
                    value: 0
                });
                if (self.args.length == 1) return make_node(AST_UnaryPrefix, self, {
                    expression: self.args[0],
                    operator: "+"
                }).optimize(compressor);
              case "Boolean":
                if (self.args.length == 0) return make_node(AST_False, self);
                if (self.args.length == 1) return make_node(AST_UnaryPrefix, self, {
                    expression: make_node(AST_UnaryPrefix, self, {
                        expression: self.args[0],
                        operator: "!"
                    }),
                    operator: "!"
                }).optimize(compressor);
                break;
              case "RegExp":
                var params = [];
                if (all(self.args, function(arg) {
                    var value = arg.evaluate(compressor);
                    params.unshift(value);
                    return arg !== value;
                })) {
                    try {
                        return best_of(compressor, self, make_node(AST_RegExp, self, {
                            value: RegExp.apply(RegExp, params),
                        }));
                    } catch (ex) {
                        compressor.warn("Error converting {expr} [{file}:{line},{col}]", {
                            expr: self.print_to_string(),
                            file: self.start.file,
                            line: self.start.line,
                            col: self.start.col
                        });
                    }
                }
                break;
              case "Symbol":
                // Symbol's argument is only used for debugging.
                self.args = [];
                return self;
            } else if (exp instanceof AST_Dot) switch(exp.property) {
              case "toString":
                if (self.args.length == 0 && !exp.expression.may_throw_on_access(compressor)) {
                    return make_node(AST_Binary, self, {
                        left: make_node(AST_String, self, { value: "" }),
                        operator: "+",
                        right: exp.expression
                    }).optimize(compressor);
                }
                break;
              case "join":
                if (exp.expression instanceof AST_Array) EXIT: {
                    var separator;
                    if (self.args.length > 0) {
                        separator = self.args[0].evaluate(compressor);
                        if (separator === self.args[0]) break EXIT; // not a constant
                    }
                    var elements = [];
                    var consts = [];
                    for (var i = 0, len = exp.expression.elements.length; i < len; i++) {
                        var el = exp.expression.elements[i];
                        if (el instanceof AST_Expansion) break EXIT;
                        var value = el.evaluate(compressor);
                        if (value !== el) {
                            consts.push(value);
                        } else {
                            if (consts.length > 0) {
                                elements.push(make_node(AST_String, self, {
                                    value: consts.join(separator)
                                }));
                                consts.length = 0;
                            }
                            elements.push(el);
                        }
                    }
                    if (consts.length > 0) {
                        elements.push(make_node(AST_String, self, {
                            value: consts.join(separator)
                        }));
                    }
                    if (elements.length == 0) return make_node(AST_String, self, { value: "" });
                    if (elements.length == 1) {
                        if (elements[0].is_string(compressor)) {
                            return elements[0];
                        }
                        return make_node(AST_Binary, elements[0], {
                            operator : "+",
                            left     : make_node(AST_String, self, { value: "" }),
                            right    : elements[0]
                        });
                    }
                    if (separator == "") {
                        var first;
                        if (elements[0].is_string(compressor)
                            || elements[1].is_string(compressor)) {
                            first = elements.shift();
                        } else {
                            first = make_node(AST_String, self, { value: "" });
                        }
                        return elements.reduce(function(prev, el){
                            return make_node(AST_Binary, el, {
                                operator : "+",
                                left     : prev,
                                right    : el
                            });
                        }, first).optimize(compressor);
                    }
                    // need this awkward cloning to not affect original element
                    // best_of will decide which one to get through.
                    var node = self.clone();
                    node.expression = node.expression.clone();
                    node.expression.expression = node.expression.expression.clone();
                    node.expression.expression.elements = elements;
                    return best_of(compressor, self, node);
                }
                break;
              case "charAt":
                if (exp.expression.is_string(compressor)) {
                    var arg = self.args[0];
                    var index = arg ? arg.evaluate(compressor) : 0;
                    if (index !== arg) {
                        return make_node(AST_Sub, exp, {
                            expression: exp.expression,
                            property: make_node_from_constant(index | 0, arg || exp)
                        }).optimize(compressor);
                    }
                }
                break;
              case "apply":
                if (self.args.length == 2 && self.args[1] instanceof AST_Array) {
                    var args = self.args[1].elements.slice();
                    args.unshift(self.args[0]);
                    return make_node(AST_Call, self, {
                        expression: make_node(AST_Dot, exp, {
                            expression: exp.expression,
                            property: "call"
                        }),
                        args: args
                    }).optimize(compressor);
                }
                break;
              case "call":
                var func = exp.expression;
                if (func instanceof AST_SymbolRef) {
                    func = func.fixed_value();
                }
                if (func instanceof AST_Lambda && !func.contains_this()) {
                    return make_sequence(this, [
                        self.args[0],
                        make_node(AST_Call, self, {
                            expression: exp.expression,
                            args: self.args.slice(1)
                        })
                    ]).optimize(compressor);
                }
                break;
            }
        }
        if (compressor.option("unsafe_Function")
            && is_undeclared_ref(exp)
            && exp.name == "Function") {
            // new Function() => function(){}
            if (self.args.length == 0) return make_node(AST_Function, self, {
                argnames: [],
                body: []
            }).optimize(compressor);
            if (all(self.args, function(x) {
                return x instanceof AST_String;
            })) {
                // quite a corner-case, but we can handle it:
                //   https://github.com/mishoo/UglifyJS2/issues/203
                // if the code argument is a constant, then we can minify it.
                try {
                    var code = "n(function(" + self.args.slice(0, -1).map(function(arg) {
                        return arg.value;
                    }).join(",") + "){" + self.args[self.args.length - 1].value + "})";
                    var ast = parse(code);
                    var mangle = { ie8: compressor.option("ie8") };
                    ast.figure_out_scope(mangle);
                    var comp = new Compressor(compressor.options);
                    ast = ast.transform(comp);
                    ast.figure_out_scope(mangle);
                    base54.reset();
                    ast.compute_char_frequency(mangle);
                    ast.mangle_names(mangle);
                    var fun;
                    ast.walk(new TreeWalker(function(node) {
                        if (fun) return true;
                        if (is_func_expr(node)) {
                            fun = node;
                            return true;
                        }
                    }));
                    if (fun.body instanceof AST_Node) {
                        fun.body = [
                            make_node(AST_Return, fun.body, {
                                value: fun.body
                            })
                        ];
                    }
                    var code = OutputStream();
                    AST_BlockStatement.prototype._codegen.call(fun, fun, code);
                    self.args = [
                        make_node(AST_String, self, {
                            value: fun.argnames.map(function(arg) {
                                return arg.print_to_string();
                            }).join(",")
                        }),
                        make_node(AST_String, self.args[self.args.length - 1], {
                            value: code.get().replace(/^\{|\}$/g, "")
                        })
                    ];
                    return self;
                } catch (ex) {
                    if (ex instanceof JS_Parse_Error) {
                        compressor.warn("Error parsing code passed to new Function [{file}:{line},{col}]", self.args[self.args.length - 1].start);
                        compressor.warn(ex.toString());
                    } else {
                        throw ex;
                    }
                }
            }
        }
        var stat = is_func && fn.body;
        if (stat instanceof AST_Node) {
            stat = make_node(AST_Return, stat, {
                value: stat
            });
        } else if (stat) {
            stat = stat[0];
        }
        if (compressor.option("inline") && stat instanceof AST_Return) {
            var value = stat.value;
            if (!value || value.is_constant_expression()) {
                var args = self.args.concat(value || make_node(AST_Undefined, self));
                return make_sequence(self, args).optimize(compressor);
            }
        }
        if (is_func && !fn.is_generator && !fn.async) {
            var def, value, scope, in_loop, level = -1;
            if (compressor.option("inline")
                && simple_args
                && !fn.uses_arguments
                && !fn.uses_eval
                && !(fn.name && fn instanceof AST_Function)
                && (!(compressor.find_parent(AST_Lambda) instanceof AST_Arrow)
                    || fn.argnames.length == 0
                        && (fn.body instanceof AST_Node || fn.body.length == 1))
                && (value = can_flatten_body(stat))
                && (exp === fn
                    || compressor.option("unused")
                        && (def = exp.definition()).references.length == 1
                        && !recursive_ref(compressor, def)
                        && fn.is_constant_expression(exp.scope))
                && !self.pure
                && !fn.contains_this()
                && can_inject_symbols()) {
                return make_sequence(self, flatten_fn()).optimize(compressor);
            }
            if (compressor.option("side_effects") && !(fn.body instanceof AST_Node) && all(fn.body, is_empty)) {
                var args = self.args.concat(make_node(AST_Undefined, self));
                return make_sequence(self, args).optimize(compressor);
            }
        }
        if (compressor.option("drop_console")) {
            if (exp instanceof AST_PropAccess) {
                var name = exp.expression;
                while (name.expression) {
                    name = name.expression;
                }
                if (is_undeclared_ref(name) && name.name == "console") {
                    return make_node(AST_Undefined, self).optimize(compressor);
                }
            }
        }
        if (compressor.option("negate_iife")
            && compressor.parent() instanceof AST_SimpleStatement
            && is_iife_call(self)) {
            return self.negate(compressor, true);
        }
        var ev = self.evaluate(compressor);
        if (ev !== self) {
            ev = make_node_from_constant(ev, self).optimize(compressor);
            return best_of(compressor, ev, self);
        }
        return self;

        function return_value(stat) {
            if (!stat) return make_node(AST_Undefined, self);
            if (stat instanceof AST_Return) {
                if (!stat.value) return make_node(AST_Undefined, self);
                return stat.value.clone(true);
            }
            if (stat instanceof AST_SimpleStatement) {
                return make_node(AST_UnaryPrefix, stat, {
                    operator: "void",
                    expression: stat.body.clone(true)
                });
            }
        }

        function can_flatten_body(stat) {
            var body = fn.body instanceof AST_Node ? [ fn.body ] : fn.body;
            var len = body.length;
            if (compressor.option("inline") < 3) {
                return len == 1 && return_value(stat);
            }
            stat = null;
            for (var i = 0; i < len; i++) {
                var line = body[i];
                if (line instanceof AST_Var) {
                    if (stat && !all(line.definitions, function(var_def) {
                        return !var_def.value;
                    })) {
                        return false;
                    }
                } else if (stat) {
                    return false;
                } else {
                    stat = line;
                }
            }
            return return_value(stat);
        }

        function can_inject_args(catches, safe_to_inject) {
            for (var i = 0, len = fn.argnames.length; i < len; i++) {
                var arg = fn.argnames[i];
                if (arg instanceof AST_DefaultAssign) {
                    if (arg.left.__unused) continue;
                    return false;
                }
                if (arg instanceof AST_Destructuring) return false;
                if (arg instanceof AST_Expansion) {
                    if (arg.expression.__unused) continue;
                    return false;
                }
                if (arg.__unused) continue;
                if (!safe_to_inject
                    || catches[arg.name]
                    || identifier_atom(arg.name)
                    || scope.var_names()[arg.name]) {
                    return false;
                }
                if (in_loop) in_loop.push(arg.definition());
            }
            return true;
        }

        function can_inject_vars(catches, safe_to_inject) {
            var len = fn.body.length;
            for (var i = 0; i < len; i++) {
                var stat = fn.body[i];
                if (!(stat instanceof AST_Var)) continue;
                if (!safe_to_inject) return false;
                for (var j = stat.definitions.length; --j >= 0;) {
                    var name = stat.definitions[j].name;
                    if (catches[name.name]
                        || identifier_atom(name.name)
                        || scope.var_names()[name.name]) {
                        return false;
                    }
                    if (in_loop) in_loop.push(name.definition());
                }
            }
            return true;
        }

        function can_inject_symbols() {
            var catches = Object.create(null);
            do {
                scope = compressor.parent(++level);
                if (scope instanceof AST_Catch) {
                    catches[scope.argname.name] = true;
                } else if (scope instanceof AST_IterationStatement) {
                    in_loop = [];
                } else if (scope instanceof AST_SymbolRef) {
                    if (scope.fixed_value() instanceof AST_Scope) return false;
                }
            } while (!(scope instanceof AST_Scope) || scope instanceof AST_Arrow);
            var safe_to_inject = !(scope instanceof AST_Toplevel) || compressor.toplevel.vars;
            var inline = compressor.option("inline");
            if (!can_inject_vars(catches, inline >= 3 && safe_to_inject)) return false;
            if (!can_inject_args(catches, inline >= 2 && safe_to_inject)) return false;
            return !in_loop || in_loop.length == 0 || !is_reachable(fn, in_loop);
        }

        function append_var(decls, expressions, name, value) {
            var def = name.definition();
            scope.variables.set(name.name, def);
            scope.enclosed.push(def);
            if (!scope.var_names()[name.name]) {
                scope.var_names()[name.name] = true;
                decls.push(make_node(AST_VarDef, name, {
                    name: name,
                    value: null
                }));
            }
            var sym = make_node(AST_SymbolRef, name, name);
            def.references.push(sym);
            if (value) expressions.push(make_node(AST_Assign, self, {
                operator: "=",
                left: sym,
                right: value
            }));
        }

        function flatten_args(decls, expressions) {
            var len = fn.argnames.length;
            for (var i = self.args.length; --i >= len;) {
                expressions.push(self.args[i]);
            }
            for (i = len; --i >= 0;) {
                var name = fn.argnames[i];
                var value = self.args[i];
                if (name.__unused || !name.name || scope.var_names()[name.name]) {
                    if (value) expressions.push(value);
                } else {
                    var symbol = make_node(AST_SymbolVar, name, name);
                    name.definition().orig.push(symbol);
                    if (!value && in_loop) value = make_node(AST_Undefined, self);
                    append_var(decls, expressions, symbol, value);
                }
            }
            decls.reverse();
            expressions.reverse();
        }

        function flatten_vars(decls, expressions) {
            var pos = expressions.length;
            for (var i = 0, lines = fn.body.length; i < lines; i++) {
                var stat = fn.body[i];
                if (!(stat instanceof AST_Var)) continue;
                for (var j = 0, defs = stat.definitions.length; j < defs; j++) {
                    var var_def = stat.definitions[j];
                    var name = var_def.name;
                    append_var(decls, expressions, name, var_def.value);
                    if (in_loop) {
                        var def = name.definition();
                        var sym = make_node(AST_SymbolRef, name, name);
                        def.references.push(sym);
                        expressions.splice(pos++, 0, make_node(AST_Assign, var_def, {
                            operator: "=",
                            left: sym,
                            right: make_node(AST_Undefined, name)
                        }));
                    }
                }
            }
        }

        function flatten_fn() {
            var decls = [];
            var expressions = [];
            flatten_args(decls, expressions);
            flatten_vars(decls, expressions);
            expressions.push(value);
            if (decls.length) {
                i = scope.body.indexOf(compressor.parent(level - 1)) + 1;
                scope.body.splice(i, 0, make_node(AST_Var, fn, {
                    definitions: decls
                }));
            }
            return expressions;
        }
    });

    OPT(AST_New, function(self, compressor){
        if (compressor.option("unsafe")) {
            var exp = self.expression;
            if (is_undeclared_ref(exp)) {
                switch (exp.name) {
                  case "Object":
                  case "RegExp":
                  case "Function":
                  case "Error":
                  case "Array":
                    return make_node(AST_Call, self, self).transform(compressor);
                }
            }
        }
        return self;
    });

    OPT(AST_Sequence, function(self, compressor){
        if (!compressor.option("side_effects")) return self;
        var expressions = [];
        filter_for_side_effects();
        var end = expressions.length - 1;
        trim_right_for_undefined();
        if (end == 0) {
            self = maintain_this_binding(compressor.parent(), compressor.self(), expressions[0]);
            if (!(self instanceof AST_Sequence)) self = self.optimize(compressor);
            return self;
        }
        self.expressions = expressions;
        return self;

        function filter_for_side_effects() {
            var first = first_in_statement(compressor);
            var last = self.expressions.length - 1;
            self.expressions.forEach(function(expr, index) {
                if (index < last) expr = expr.drop_side_effect_free(compressor, first);
                if (expr) {
                    merge_sequence(expressions, expr);
                    first = false;
                }
            });
        }

        function trim_right_for_undefined() {
            while (end > 0 && is_undefined(expressions[end], compressor)) end--;
            if (end < expressions.length - 1) {
                expressions[end] = make_node(AST_UnaryPrefix, self, {
                    operator   : "void",
                    expression : expressions[end]
                });
                expressions.length = end + 1;
            }
        }
    });

    AST_Unary.DEFMETHOD("lift_sequences", function(compressor){
        if (compressor.option("sequences")) {
            if (this.expression instanceof AST_Sequence) {
                var x = this.expression.expressions.slice();
                var e = this.clone();
                e.expression = x.pop();
                x.push(e);
                return make_sequence(this, x).optimize(compressor);
            }
        }
        return this;
    });

    OPT(AST_UnaryPostfix, function(self, compressor){
        return self.lift_sequences(compressor);
    });

    OPT(AST_UnaryPrefix, function(self, compressor){
        var e = self.expression;
        if (self.operator == "delete"
            && !(e instanceof AST_SymbolRef
                || e instanceof AST_PropAccess
                || is_identifier_atom(e))) {
            if (e instanceof AST_Sequence) {
                e = e.expressions.slice();
                e.push(make_node(AST_True, self));
                return make_sequence(self, e).optimize(compressor);
            }
            return make_sequence(self, [ e, make_node(AST_True, self) ]).optimize(compressor);
        }
        var seq = self.lift_sequences(compressor);
        if (seq !== self) {
            return seq;
        }
        if (compressor.option("side_effects") && self.operator == "void") {
            e = e.drop_side_effect_free(compressor);
            if (e) {
                self.expression = e;
                return self;
            } else {
                return make_node(AST_Undefined, self).optimize(compressor);
            }
        }
        if (compressor.in_boolean_context()) {
            switch (self.operator) {
              case "!":
                if (e instanceof AST_UnaryPrefix && e.operator == "!") {
                    // !!foo ==> foo, if we're in boolean context
                    return e.expression;
                }
                if (e instanceof AST_Binary) {
                    self = best_of(compressor, self, e.negate(compressor, first_in_statement(compressor)));
                }
                break;
              case "typeof":
                // typeof always returns a non-empty string, thus it's
                // always true in booleans
                compressor.warn("Boolean expression always true [{file}:{line},{col}]", self.start);
                return (e instanceof AST_SymbolRef ? make_node(AST_True, self) : make_sequence(self, [
                    e,
                    make_node(AST_True, self)
                ])).optimize(compressor);
            }
        }
        if (self.operator == "-" && e instanceof AST_Infinity) {
            e = e.transform(compressor);
        }
        if (e instanceof AST_Binary
            && (self.operator == "+" || self.operator == "-")
            && (e.operator == "*" || e.operator == "/" || e.operator == "%")) {
            return make_node(AST_Binary, self, {
                operator: e.operator,
                left: make_node(AST_UnaryPrefix, e.left, {
                    operator: self.operator,
                    expression: e.left
                }),
                right: e.right
            });
        }
        // avoids infinite recursion of numerals
        if (self.operator != "-"
            || !(e instanceof AST_Number || e instanceof AST_Infinity)) {
            var ev = self.evaluate(compressor);
            if (ev !== self) {
                ev = make_node_from_constant(ev, self).optimize(compressor);
                return best_of(compressor, ev, self);
            }
        }
        return self;
    });

    AST_Binary.DEFMETHOD("lift_sequences", function(compressor){
        if (compressor.option("sequences")) {
            if (this.left instanceof AST_Sequence) {
                var x = this.left.expressions.slice();
                var e = this.clone();
                e.left = x.pop();
                x.push(e);
                return make_sequence(this, x).optimize(compressor);
            }
            if (this.right instanceof AST_Sequence && !this.left.has_side_effects(compressor)) {
                var assign = this.operator == "=" && this.left instanceof AST_SymbolRef;
                var x = this.right.expressions;
                var last = x.length - 1;
                for (var i = 0; i < last; i++) {
                    if (!assign && x[i].has_side_effects(compressor)) break;
                }
                if (i == last) {
                    x = x.slice();
                    var e = this.clone();
                    e.right = x.pop();
                    x.push(e);
                    return make_sequence(this, x).optimize(compressor);
                } else if (i > 0) {
                    var e = this.clone();
                    e.right = make_sequence(this.right, x.slice(i));
                    x = x.slice(0, i);
                    x.push(e);
                    return make_sequence(this, x).optimize(compressor);
                }
            }
        }
        return this;
    });

    var commutativeOperators = makePredicate("== === != !== * & | ^");
    function is_object(node) {
        return node instanceof AST_Array
            || node instanceof AST_Lambda
            || node instanceof AST_Object
            || node instanceof AST_Class;
    }

    OPT(AST_Binary, function(self, compressor){
        function reversible() {
            return self.left.is_constant()
                || self.right.is_constant()
                || !self.left.has_side_effects(compressor)
                    && !self.right.has_side_effects(compressor);
        }
        function reverse(op) {
            if (reversible()) {
                if (op) self.operator = op;
                var tmp = self.left;
                self.left = self.right;
                self.right = tmp;
            }
        }
        if (commutativeOperators(self.operator)) {
            if (self.right.is_constant()
                && !self.left.is_constant()) {
                // if right is a constant, whatever side effects the
                // left side might have could not influence the
                // result.  hence, force switch.

                if (!(self.left instanceof AST_Binary
                      && PRECEDENCE[self.left.operator] >= PRECEDENCE[self.operator])) {
                    reverse();
                }
            }
        }
        self = self.lift_sequences(compressor);
        if (compressor.option("comparisons")) switch (self.operator) {
          case "===":
          case "!==":
            var is_strict_comparison = true;
            if ((self.left.is_string(compressor) && self.right.is_string(compressor)) ||
                (self.left.is_number(compressor) && self.right.is_number(compressor)) ||
                (self.left.is_boolean() && self.right.is_boolean()) ||
                self.left.equivalent_to(self.right)) {
                self.operator = self.operator.substr(0, 2);
            }
            // XXX: intentionally falling down to the next case
          case "==":
          case "!=":
            // void 0 == x => null == x
            if (!is_strict_comparison && is_undefined(self.left, compressor)) {
                self.left = make_node(AST_Null, self.left);
            }
            // "undefined" == typeof x => undefined === x
            else if (compressor.option("typeofs")
                && self.left instanceof AST_String
                && self.left.value == "undefined"
                && self.right instanceof AST_UnaryPrefix
                && self.right.operator == "typeof") {
                var expr = self.right.expression;
                if (expr instanceof AST_SymbolRef ? expr.is_declared(compressor)
                    : !(expr instanceof AST_PropAccess && compressor.option("ie8"))) {
                    self.right = expr;
                    self.left = make_node(AST_Undefined, self.left).optimize(compressor);
                    if (self.operator.length == 2) self.operator += "=";
                }
            }
            // obj !== obj => false
            else if (self.left instanceof AST_SymbolRef
                && self.right instanceof AST_SymbolRef
                && self.left.definition() === self.right.definition()
                && is_object(self.left.fixed_value())) {
                return make_node(self.operator[0] == "=" ? AST_True : AST_False, self);
            }
            break;
          case "&&":
          case "||":
            var lhs = self.left;
            if (lhs.operator == self.operator) {
                lhs = lhs.right;
            }
            if (lhs instanceof AST_Binary
                && lhs.operator == (self.operator == "&&" ? "!==" : "===")
                && self.right instanceof AST_Binary
                && lhs.operator == self.right.operator
                && (is_undefined(lhs.left, compressor) && self.right.left instanceof AST_Null
                    || lhs.left instanceof AST_Null && is_undefined(self.right.left, compressor))
                && !lhs.right.has_side_effects(compressor)
                && lhs.right.equivalent_to(self.right.right)) {
                var combined = make_node(AST_Binary, self, {
                    operator: lhs.operator.slice(0, -1),
                    left: make_node(AST_Null, self),
                    right: lhs.right
                });
                if (lhs !== self.left) {
                    combined = make_node(AST_Binary, self, {
                        operator: self.operator,
                        left: self.left.left,
                        right: combined
                    });
                }
                return combined;
            }
            break;
        }
        if (self.operator == "+" && compressor.in_boolean_context()) {
            var ll = self.left.evaluate(compressor);
            var rr = self.right.evaluate(compressor);
            if (ll && typeof ll == "string") {
                compressor.warn("+ in boolean context always true [{file}:{line},{col}]", self.start);
                return make_sequence(self, [
                    self.right,
                    make_node(AST_True, self)
                ]).optimize(compressor);
            }
            if (rr && typeof rr == "string") {
                compressor.warn("+ in boolean context always true [{file}:{line},{col}]", self.start);
                return make_sequence(self, [
                    self.left,
                    make_node(AST_True, self)
                ]).optimize(compressor);
            }
        }
        if (compressor.option("comparisons") && self.is_boolean()) {
            if (!(compressor.parent() instanceof AST_Binary)
                || compressor.parent() instanceof AST_Assign) {
                var negated = make_node(AST_UnaryPrefix, self, {
                    operator: "!",
                    expression: self.negate(compressor, first_in_statement(compressor))
                });
                self = best_of(compressor, self, negated);
            }
            if (compressor.option("unsafe_comps")) {
                switch (self.operator) {
                  case "<": reverse(">"); break;
                  case "<=": reverse(">="); break;
                }
            }
        }
        if (self.operator == "+") {
            if (self.right instanceof AST_String
                && self.right.getValue() == ""
                && self.left.is_string(compressor)) {
                return self.left;
            }
            if (self.left instanceof AST_String
                && self.left.getValue() == ""
                && self.right.is_string(compressor)) {
                return self.right;
            }
            if (self.left instanceof AST_Binary
                && self.left.operator == "+"
                && self.left.left instanceof AST_String
                && self.left.left.getValue() == ""
                && self.right.is_string(compressor)) {
                self.left = self.left.right;
                return self.transform(compressor);
            }
        }
        if (compressor.option("evaluate")) {
            switch (self.operator) {
              case "&&":
                var ll = self.left.truthy ? true : self.left.falsy ? false : self.left.evaluate(compressor);
                if (!ll) {
                    compressor.warn("Condition left of && always false [{file}:{line},{col}]", self.start);
                    return maintain_this_binding(compressor.parent(), compressor.self(), self.left).optimize(compressor);
                } else if (!(ll instanceof AST_Node)) {
                    compressor.warn("Condition left of && always true [{file}:{line},{col}]", self.start);
                    return make_sequence(self, [ self.left, self.right ]).optimize(compressor);
                }
                var rr = self.right.evaluate(compressor);
                if (!rr) {
                    if (compressor.in_boolean_context()) {
                        compressor.warn("Boolean && always false [{file}:{line},{col}]", self.start);
                        return make_sequence(self, [
                            self.left,
                            make_node(AST_False, self)
                        ]).optimize(compressor);
                    } else self.falsy = true;
                } else if (!(rr instanceof AST_Node)) {
                    var parent = compressor.parent();
                    if (parent.operator == "&&" && parent.left === compressor.self() || compressor.in_boolean_context()) {
                        compressor.warn("Dropping side-effect-free && [{file}:{line},{col}]", self.start);
                        return self.left.optimize(compressor);
                    }
                }
                // x || false && y ---> x ? y : false
                if (self.left.operator == "||") {
                    var lr = self.left.right.evaluate(compressor);
                    if (!lr) return make_node(AST_Conditional, self, {
                        condition: self.left.left,
                        consequent: self.right,
                        alternative: self.left.right
                    }).optimize(compressor);
                }
                break;
              case "||":
                var ll = self.left.truthy ? true : self.left.falsy ? false : self.left.evaluate(compressor);
                if (!ll) {
                    compressor.warn("Condition left of || always false [{file}:{line},{col}]", self.start);
                    return make_sequence(self, [ self.left, self.right ]).optimize(compressor);
                } else if (!(ll instanceof AST_Node)) {
                    compressor.warn("Condition left of || always true [{file}:{line},{col}]", self.start);
                    return maintain_this_binding(compressor.parent(), compressor.self(), self.left).optimize(compressor);
                }
                var rr = self.right.evaluate(compressor);
                if (!rr) {
                    var parent = compressor.parent();
                    if (parent.operator == "||" && parent.left === compressor.self() || compressor.in_boolean_context()) {
                        compressor.warn("Dropping side-effect-free || [{file}:{line},{col}]", self.start);
                        return self.left.optimize(compressor);
                    }
                } else if (!(rr instanceof AST_Node)) {
                    if (compressor.in_boolean_context()) {
                        compressor.warn("Boolean || always true [{file}:{line},{col}]", self.start);
                        return make_sequence(self, [
                            self.left,
                            make_node(AST_True, self)
                        ]).optimize(compressor);
                    } else self.truthy = true;
                }
                if (self.left.operator == "&&") {
                    var lr = self.left.right.evaluate(compressor);
                    if (lr && !(lr instanceof AST_Node)) return make_node(AST_Conditional, self, {
                        condition: self.left.left,
                        consequent: self.left.right,
                        alternative: self.right
                    }).optimize(compressor);
                }
                break;
            }
            var associative = true;
            switch (self.operator) {
              case "+":
                // "foo" + ("bar" + x) => "foobar" + x
                if (self.left instanceof AST_Constant
                    && self.right instanceof AST_Binary
                    && self.right.operator == "+"
                    && self.right.left instanceof AST_Constant
                    && self.right.is_string(compressor)) {
                    self = make_node(AST_Binary, self, {
                        operator: "+",
                        left: make_node(AST_String, self.left, {
                            value: "" + self.left.getValue() + self.right.left.getValue(),
                            start: self.left.start,
                            end: self.right.left.end
                        }),
                        right: self.right.right
                    });
                }
                // (x + "foo") + "bar" => x + "foobar"
                if (self.right instanceof AST_Constant
                    && self.left instanceof AST_Binary
                    && self.left.operator == "+"
                    && self.left.right instanceof AST_Constant
                    && self.left.is_string(compressor)) {
                    self = make_node(AST_Binary, self, {
                        operator: "+",
                        left: self.left.left,
                        right: make_node(AST_String, self.right, {
                            value: "" + self.left.right.getValue() + self.right.getValue(),
                            start: self.left.right.start,
                            end: self.right.end
                        })
                    });
                }
                // (x + "foo") + ("bar" + y) => (x + "foobar") + y
                if (self.left instanceof AST_Binary
                    && self.left.operator == "+"
                    && self.left.is_string(compressor)
                    && self.left.right instanceof AST_Constant
                    && self.right instanceof AST_Binary
                    && self.right.operator == "+"
                    && self.right.left instanceof AST_Constant
                    && self.right.is_string(compressor)) {
                    self = make_node(AST_Binary, self, {
                        operator: "+",
                        left: make_node(AST_Binary, self.left, {
                            operator: "+",
                            left: self.left.left,
                            right: make_node(AST_String, self.left.right, {
                                value: "" + self.left.right.getValue() + self.right.left.getValue(),
                                start: self.left.right.start,
                                end: self.right.left.end
                            })
                        }),
                        right: self.right.right
                    });
                }
                // a + -b => a - b
                if (self.right instanceof AST_UnaryPrefix
                    && self.right.operator == "-"
                    && self.left.is_number(compressor)) {
                    self = make_node(AST_Binary, self, {
                        operator: "-",
                        left: self.left,
                        right: self.right.expression
                    });
                    break;
                }
                // -a + b => b - a
                if (self.left instanceof AST_UnaryPrefix
                    && self.left.operator == "-"
                    && reversible()
                    && self.right.is_number(compressor)) {
                    self = make_node(AST_Binary, self, {
                        operator: "-",
                        left: self.right,
                        right: self.left.expression
                    });
                    break;
                }
              case "*":
                associative = compressor.option("unsafe_math");
              case "&":
              case "|":
              case "^":
                // a + +b => +b + a
                if (self.left.is_number(compressor)
                    && self.right.is_number(compressor)
                    && reversible()
                    && !(self.left instanceof AST_Binary
                        && self.left.operator != self.operator
                        && PRECEDENCE[self.left.operator] >= PRECEDENCE[self.operator])) {
                    var reversed = make_node(AST_Binary, self, {
                        operator: self.operator,
                        left: self.right,
                        right: self.left
                    });
                    if (self.right instanceof AST_Constant
                        && !(self.left instanceof AST_Constant)) {
                        self = best_of(compressor, reversed, self);
                    } else {
                        self = best_of(compressor, self, reversed);
                    }
                }
                if (associative && self.is_number(compressor)) {
                    // a + (b + c) => (a + b) + c
                    if (self.right instanceof AST_Binary
                        && self.right.operator == self.operator) {
                        self = make_node(AST_Binary, self, {
                            operator: self.operator,
                            left: make_node(AST_Binary, self.left, {
                                operator: self.operator,
                                left: self.left,
                                right: self.right.left,
                                start: self.left.start,
                                end: self.right.left.end
                            }),
                            right: self.right.right
                        });
                    }
                    // (n + 2) + 3 => 5 + n
                    // (2 * n) * 3 => 6 + n
                    if (self.right instanceof AST_Constant
                        && self.left instanceof AST_Binary
                        && self.left.operator == self.operator) {
                        if (self.left.left instanceof AST_Constant) {
                            self = make_node(AST_Binary, self, {
                                operator: self.operator,
                                left: make_node(AST_Binary, self.left, {
                                    operator: self.operator,
                                    left: self.left.left,
                                    right: self.right,
                                    start: self.left.left.start,
                                    end: self.right.end
                                }),
                                right: self.left.right
                            });
                        } else if (self.left.right instanceof AST_Constant) {
                            self = make_node(AST_Binary, self, {
                                operator: self.operator,
                                left: make_node(AST_Binary, self.left, {
                                    operator: self.operator,
                                    left: self.left.right,
                                    right: self.right,
                                    start: self.left.right.start,
                                    end: self.right.end
                                }),
                                right: self.left.left
                            });
                        }
                    }
                    // (a | 1) | (2 | d) => (3 | a) | b
                    if (self.left instanceof AST_Binary
                        && self.left.operator == self.operator
                        && self.left.right instanceof AST_Constant
                        && self.right instanceof AST_Binary
                        && self.right.operator == self.operator
                        && self.right.left instanceof AST_Constant) {
                        self = make_node(AST_Binary, self, {
                            operator: self.operator,
                            left: make_node(AST_Binary, self.left, {
                                operator: self.operator,
                                left: make_node(AST_Binary, self.left.left, {
                                    operator: self.operator,
                                    left: self.left.right,
                                    right: self.right.left,
                                    start: self.left.right.start,
                                    end: self.right.left.end
                                }),
                                right: self.left.left
                            }),
                            right: self.right.right
                        });
                    }
                }
            }
        }
        // x && (y && z)  ==>  x && y && z
        // x || (y || z)  ==>  x || y || z
        // x + ("y" + z)  ==>  x + "y" + z
        // "x" + (y + "z")==>  "x" + y + "z"
        if (self.right instanceof AST_Binary
            && self.right.operator == self.operator
            && (lazy_op(self.operator)
                || (self.operator == "+"
                    && (self.right.left.is_string(compressor)
                        || (self.left.is_string(compressor)
                            && self.right.right.is_string(compressor))))))
        {
            self.left = make_node(AST_Binary, self.left, {
                operator : self.operator,
                left     : self.left,
                right    : self.right.left
            });
            self.right = self.right.right;
            return self.transform(compressor);
        }
        var ev = self.evaluate(compressor);
        if (ev !== self) {
            ev = make_node_from_constant(ev, self).optimize(compressor);
            return best_of(compressor, ev, self);
        }
        return self;
    });

    OPT(AST_SymbolExport, function(self, compressor){
        return self;
    });

    function recursive_ref(compressor, def) {
        var node;
        for (var i = 0; node = compressor.parent(i); i++) {
            if (node instanceof AST_Lambda) {
                var name = node.name;
                if (name && name.definition() === def) break;
            }
        }
        return node;
    }

    OPT(AST_SymbolRef, function(self, compressor){
        var def = self.resolve_defines(compressor);
        if (def) {
            return def.optimize(compressor);
        }
        // testing against !self.scope.uses_with first is an optimization
        if (!compressor.option("ie8")
            && is_undeclared_ref(self)
            && (!self.scope.uses_with || !compressor.find_parent(AST_With))) {
            switch (self.name) {
              case "undefined":
                return make_node(AST_Undefined, self).optimize(compressor);
              case "NaN":
                return make_node(AST_NaN, self).optimize(compressor);
              case "Infinity":
                return make_node(AST_Infinity, self).optimize(compressor);
            }
        }
        if (compressor.option("reduce_vars")
            && is_lhs(self, compressor.parent()) !== self) {
            var d = self.definition();
            var fixed = self.fixed_value();
            var single_use = d.single_use;
            if (single_use && (fixed instanceof AST_Lambda || fixed instanceof AST_Class)) {
                if (d.scope !== self.scope
                    && (!compressor.option("reduce_funcs") && fixed instanceof AST_Lambda
                        || d.escaped == 1
                        || fixed.inlined)) {
                    single_use = false;
                } else if (recursive_ref(compressor, d)) {
                    single_use = false;
                } else if (d.scope !== self.scope || d.orig[0] instanceof AST_SymbolFunarg) {
                    single_use = fixed.is_constant_expression(self.scope);
                    if (single_use == "f") {
                        var scope = self.scope;
                        do {
                            if (scope instanceof AST_Defun || is_func_expr(scope)) {
                                scope.inlined = true;
                            }
                        } while (scope = scope.parent_scope);
                    }
                }
            }
            if (single_use && fixed) {
                if (fixed instanceof AST_DefClass) {
                    fixed = make_node(AST_ClassExpression, fixed, fixed);
                }
                if (fixed instanceof AST_Defun) {
                    fixed._squeezed = true;
                    fixed = make_node(AST_Function, fixed, fixed);
                }
                var value;
                if (d.recursive_refs > 0 && fixed.name instanceof AST_SymbolDefun) {
                    value = fixed.clone(true);
                    var defun_def = value.name.definition();
                    var lambda_def = value.variables.get(value.name.name);
                    var name = lambda_def && lambda_def.orig[0];
                    if (!(name instanceof AST_SymbolLambda)) {
                        name = make_node(AST_SymbolLambda, value.name, value.name);
                        name.scope = value;
                        value.name = name;
                        lambda_def = value.def_function(name);
                    }
                    value.walk(new TreeWalker(function(node) {
                        if (node instanceof AST_SymbolRef && node.definition() === defun_def) {
                            node.thedef = lambda_def;
                            lambda_def.references.push(node);
                        }
                    }));
                } else {
                    value = fixed.optimize(compressor);
                    if (value === fixed) value = fixed.clone(true);
                }
                return value;
            }
            if (fixed && d.should_replace === undefined) {
                var init;
                if (fixed instanceof AST_This) {
                    if (!(d.orig[0] instanceof AST_SymbolFunarg)
                        && all(d.references, function(ref) {
                            return d.scope === ref.scope;
                        })) {
                        init = fixed;
                    }
                } else {
                    var ev = fixed.evaluate(compressor);
                    if (ev !== fixed && (compressor.option("unsafe_regexp") || !(ev instanceof RegExp))) {
                        init = make_node_from_constant(ev, fixed);
                    }
                }
                if (init) {
                    var value_length = init.optimize(compressor).print_to_string().length;
                    var fn;
                    if (has_symbol_ref(fixed)) {
                        fn = function() {
                            var result = init.optimize(compressor);
                            return result === init ? result.clone(true) : result;
                        };
                    } else {
                        value_length = Math.min(value_length, fixed.print_to_string().length);
                        fn = function() {
                            var result = best_of_expression(init.optimize(compressor), fixed);
                            return result === init || result === fixed ? result.clone(true) : result;
                        };
                    }
                    var name_length = d.name.length;
                    var overhead = 0;
                    if (compressor.option("unused") && !compressor.exposed(d)) {
                        overhead = (name_length + 2 + value_length) / (d.references.length - d.assignments);
                    }
                    d.should_replace = value_length <= name_length + overhead ? fn : false;
                } else {
                    d.should_replace = false;
                }
            }
            if (d.should_replace) {
                return d.should_replace();
            }
        }
        return self;

        function has_symbol_ref(value) {
            var found;
            value.walk(new TreeWalker(function(node) {
                if (node instanceof AST_SymbolRef) found = true;
                if (found) return true;
            }));
            return found;
        }
    });

    function is_atomic(lhs, self) {
        return lhs instanceof AST_SymbolRef || lhs.TYPE === self.TYPE;
    }

    OPT(AST_Undefined, function(self, compressor){
        if (compressor.option("unsafe_undefined")) {
            var undef = find_variable(compressor, "undefined");
            if (undef) {
                var ref = make_node(AST_SymbolRef, self, {
                    name   : "undefined",
                    scope  : undef.scope,
                    thedef : undef
                });
                ref.is_undefined = true;
                return ref;
            }
        }
        var lhs = is_lhs(compressor.self(), compressor.parent());
        if (lhs && is_atomic(lhs, self)) return self;
        return make_node(AST_UnaryPrefix, self, {
            operator: "void",
            expression: make_node(AST_Number, self, {
                value: 0
            })
        });
    });

    OPT(AST_Infinity, function(self, compressor){
        var lhs = is_lhs(compressor.self(), compressor.parent());
        if (lhs && is_atomic(lhs, self)) return self;
        if (compressor.option("keep_infinity")
            && !(lhs && !is_atomic(lhs, self))
            && !find_variable(compressor, "Infinity"))
            return self;
        return make_node(AST_Binary, self, {
            operator: "/",
            left: make_node(AST_Number, self, {
                value: 1
            }),
            right: make_node(AST_Number, self, {
                value: 0
            })
        });
    });

    OPT(AST_NaN, function(self, compressor){
        var lhs = is_lhs(compressor.self(), compressor.parent());
        if (lhs && !is_atomic(lhs, self)
            || find_variable(compressor, "NaN")) {
            return make_node(AST_Binary, self, {
                operator: "/",
                left: make_node(AST_Number, self, {
                    value: 0
                }),
                right: make_node(AST_Number, self, {
                    value: 0
                })
            });
        }
        return self;
    });

    function is_reachable(self, defs) {
        var reachable = false;
        var find_ref = new TreeWalker(function(node) {
            if (reachable) return true;
            if (node instanceof AST_SymbolRef && member(node.definition(), defs)) {
                return reachable = true;
            }
        });
        var scan_scope = new TreeWalker(function(node) {
            if (reachable) return true;
            if (node instanceof AST_Scope && node !== self) {
                var parent = scan_scope.parent();
                if (parent instanceof AST_Call && parent.expression === node) return;
                node.walk(find_ref);
                return true;
            }
        });
        self.walk(scan_scope);
        return reachable;
    }

    var ASSIGN_OPS = [ '+', '-', '/', '*', '%', '>>', '<<', '>>>', '|', '^', '&' ];
    var ASSIGN_OPS_COMMUTATIVE = [ '*', '|', '^', '&' ];
    OPT(AST_Assign, function(self, compressor){
        var def;
        if (compressor.option("dead_code")
            && self.left instanceof AST_SymbolRef
            && (def = self.left.definition()).scope === compressor.find_parent(AST_Lambda)) {
            var level = 0, node, parent = self;
            do {
                node = parent;
                parent = compressor.parent(level++);
                if (parent instanceof AST_Exit) {
                    if (in_try(level, parent instanceof AST_Throw)) break;
                    if (is_reachable(def.scope, [ def ])) break;
                    if (self.operator == "=") return self.right;
                    def.fixed = false;
                    return make_node(AST_Binary, self, {
                        operator: self.operator.slice(0, -1),
                        left: self.left,
                        right: self.right
                    }).optimize(compressor);
                }
            } while (parent instanceof AST_Binary && parent.right === node
                || parent instanceof AST_Sequence && parent.tail_node() === node);
        }
        self = self.lift_sequences(compressor);
        if (self.operator == "=" && self.left instanceof AST_SymbolRef && self.right instanceof AST_Binary) {
            // x = expr1 OP expr2
            if (self.right.left instanceof AST_SymbolRef
                && self.right.left.name == self.left.name
                && member(self.right.operator, ASSIGN_OPS)) {
                // x = x - 2  --->  x -= 2
                self.operator = self.right.operator + "=";
                self.right = self.right.right;
            }
            else if (self.right.right instanceof AST_SymbolRef
                && self.right.right.name == self.left.name
                && member(self.right.operator, ASSIGN_OPS_COMMUTATIVE)
                && !self.right.left.has_side_effects(compressor)) {
                // x = 2 & x  --->  x &= 2
                self.operator = self.right.operator + "=";
                self.right = self.right.left;
            }
        }
        return self;

        function in_try(level, no_catch) {
            var scope = self.left.definition().scope;
            var parent;
            while ((parent = compressor.parent(level++)) !== scope) {
                if (parent instanceof AST_Try) {
                    if (parent.bfinally) return true;
                    if (no_catch && parent.bcatch) return true;
                }
            }
        }
    });

    OPT(AST_DefaultAssign, function(self, compressor){
        if (!compressor.option("evaluate")) {
            return self;
        }
        var evaluateRight = self.right.evaluate(compressor);

        // `[x = undefined] = foo` ---> `[x] = foo`
        if (evaluateRight === undefined) {
            self = self.left;
        } else if (evaluateRight !== self.right) {
            evaluateRight = make_node_from_constant(evaluateRight, self.right);
            self.right = best_of_expression(evaluateRight, self.right);
        }

        return self;
    });

    OPT(AST_Conditional, function(self, compressor){
        if (!compressor.option("conditionals")) return self;
        // This looks like lift_sequences(), should probably be under "sequences"
        if (self.condition instanceof AST_Sequence) {
            var expressions = self.condition.expressions.slice();
            self.condition = expressions.pop();
            expressions.push(self);
            return make_sequence(self, expressions);
        }
        var cond = self.condition.evaluate(compressor);
        if (cond !== self.condition) {
            if (cond) {
                compressor.warn("Condition always true [{file}:{line},{col}]", self.start);
                return maintain_this_binding(compressor.parent(), compressor.self(), self.consequent);
            } else {
                compressor.warn("Condition always false [{file}:{line},{col}]", self.start);
                return maintain_this_binding(compressor.parent(), compressor.self(), self.alternative);
            }
        }
        var negated = cond.negate(compressor, first_in_statement(compressor));
        if (best_of(compressor, cond, negated) === negated) {
            self = make_node(AST_Conditional, self, {
                condition: negated,
                consequent: self.alternative,
                alternative: self.consequent
            });
        }
        var condition = self.condition;
        var consequent = self.consequent;
        var alternative = self.alternative;
        // x?x:y --> x||y
        if (condition instanceof AST_SymbolRef
            && consequent instanceof AST_SymbolRef
            && condition.definition() === consequent.definition()) {
            return make_node(AST_Binary, self, {
                operator: "||",
                left: condition,
                right: alternative
            });
        }
        // if (foo) exp = something; else exp = something_else;
        //                   |
        //                   v
        // exp = foo ? something : something_else;
        if (consequent instanceof AST_Assign
            && alternative instanceof AST_Assign
            && consequent.operator == alternative.operator
            && consequent.left.equivalent_to(alternative.left)
            && (!self.condition.has_side_effects(compressor)
                || consequent.operator == "="
                    && !consequent.left.has_side_effects(compressor))) {
            return make_node(AST_Assign, self, {
                operator: consequent.operator,
                left: consequent.left,
                right: make_node(AST_Conditional, self, {
                    condition: self.condition,
                    consequent: consequent.right,
                    alternative: alternative.right
                })
            });
        }
        // x ? y(a) : y(b) --> y(x ? a : b)
        var arg_index;
        if (consequent instanceof AST_Call
            && alternative.TYPE === consequent.TYPE
            && consequent.args.length > 0
            && consequent.args.length == alternative.args.length
            && consequent.expression.equivalent_to(alternative.expression)
            && !self.condition.has_side_effects(compressor)
            && !consequent.expression.has_side_effects(compressor)
            && typeof (arg_index = single_arg_diff()) == "number") {
            var node = consequent.clone();
            node.args[arg_index] = make_node(AST_Conditional, self, {
                condition: self.condition,
                consequent: consequent.args[arg_index],
                alternative: alternative.args[arg_index]
            });
            return node;
        }
        // x?y?z:a:a --> x&&y?z:a
        if (consequent instanceof AST_Conditional
            && consequent.alternative.equivalent_to(alternative)) {
            return make_node(AST_Conditional, self, {
                condition: make_node(AST_Binary, self, {
                    left: self.condition,
                    operator: "&&",
                    right: consequent.condition
                }),
                consequent: consequent.consequent,
                alternative: alternative
            });
        }
        // x ? y : y --> x, y
        if (consequent.equivalent_to(alternative)) {
            return make_sequence(self, [
                self.condition,
                consequent
            ]).optimize(compressor);
        }
        // x ? y || z : z --> x && y || z
        if (consequent instanceof AST_Binary
            && consequent.operator == "||"
            && consequent.right.equivalent_to(alternative)) {
            return make_node(AST_Binary, self, {
                operator: "||",
                left: make_node(AST_Binary, self, {
                    operator: "&&",
                    left: self.condition,
                    right: consequent.left
                }),
                right: alternative
            }).optimize(compressor);
        }
        var in_bool = compressor.in_boolean_context();
        if (is_true(self.consequent)) {
            if (is_false(self.alternative)) {
                // c ? true : false ---> !!c
                return booleanize(self.condition);
            }
            // c ? true : x ---> !!c || x
            return make_node(AST_Binary, self, {
                operator: "||",
                left: booleanize(self.condition),
                right: self.alternative
            });
        }
        if (is_false(self.consequent)) {
            if (is_true(self.alternative)) {
                // c ? false : true ---> !c
                return booleanize(self.condition.negate(compressor));
            }
            // c ? false : x ---> !c && x
            return make_node(AST_Binary, self, {
                operator: "&&",
                left: booleanize(self.condition.negate(compressor)),
                right: self.alternative
            });
        }
        if (is_true(self.alternative)) {
            // c ? x : true ---> !c || x
            return make_node(AST_Binary, self, {
                operator: "||",
                left: booleanize(self.condition.negate(compressor)),
                right: self.consequent
            });
        }
        if (is_false(self.alternative)) {
            // c ? x : false ---> !!c && x
            return make_node(AST_Binary, self, {
                operator: "&&",
                left: booleanize(self.condition),
                right: self.consequent
            });
        }

        return self;

        function booleanize(node) {
            if (node.is_boolean()) return node;
            // !!expression
            return make_node(AST_UnaryPrefix, node, {
                operator: "!",
                expression: node.negate(compressor)
            });
        }

        // AST_True or !0
        function is_true(node) {
            return node instanceof AST_True
                || in_bool
                    && node instanceof AST_Constant
                    && node.getValue()
                || (node instanceof AST_UnaryPrefix
                    && node.operator == "!"
                    && node.expression instanceof AST_Constant
                    && !node.expression.getValue());
        }
        // AST_False or !1
        function is_false(node) {
            return node instanceof AST_False
                || in_bool
                    && node instanceof AST_Constant
                    && !node.getValue()
                || (node instanceof AST_UnaryPrefix
                    && node.operator == "!"
                    && node.expression instanceof AST_Constant
                    && node.expression.getValue());
        }

        function single_arg_diff() {
            var a = consequent.args;
            var b = alternative.args;
            for (var i = 0, len = a.length; i < len; i++) {
                if (a[i] instanceof AST_Expansion) return;
                if (!a[i].equivalent_to(b[i])) {
                    if (b[i] instanceof AST_Expansion) return;
                    for (var j = i + 1; j < len; j++) {
                        if (a[j] instanceof AST_Expansion) return;
                        if (!a[j].equivalent_to(b[j])) return;
                    }
                    return i;
                }
            }
        }
    });

    OPT(AST_Boolean, function(self, compressor){
        if (compressor.in_boolean_context()) return make_node(AST_Number, self, {
            value: +self.value
        });
        if (compressor.option("booleans")) {
            var p = compressor.parent();
            if (p instanceof AST_Binary && (p.operator == "=="
                                            || p.operator == "!=")) {
                compressor.warn("Non-strict equality against boolean: {operator} {value} [{file}:{line},{col}]", {
                    operator : p.operator,
                    value    : self.value,
                    file     : p.start.file,
                    line     : p.start.line,
                    col      : p.start.col,
                });
                return make_node(AST_Number, self, {
                    value: +self.value
                });
            }
            return make_node(AST_UnaryPrefix, self, {
                operator: "!",
                expression: make_node(AST_Number, self, {
                    value: 1 - self.value
                })
            });
        }
        return self;
    });

    OPT(AST_Sub, function(self, compressor){
        var expr = self.expression;
        var prop = self.property;
        if (compressor.option("properties")) {
            var key = prop.evaluate(compressor);
            if (key !== prop) {
                if (typeof key == "string") {
                    if (key == "undefined") {
                        key = undefined;
                    } else {
                        var value = parseFloat(key);
                        if (value.toString() == key) {
                            key = value;
                        }
                    }
                }
                prop = self.property = best_of_expression(prop, make_node_from_constant(key, prop).transform(compressor));
                var property = "" + key;
                if (is_identifier_string(property)
                    && property.length <= prop.print_to_string().length + 1) {
                    return make_node(AST_Dot, self, {
                        expression: expr,
                        property: property
                    }).optimize(compressor);
                }
            }
        }
        if (is_lhs(self, compressor.parent())) return self;
        if (key !== prop) {
            var sub = self.flatten_object(property, compressor);
            if (sub) {
                expr = self.expression = sub.expression;
                prop = self.property = sub.property;
            }
        }
        if (compressor.option("properties") && compressor.option("side_effects")
            && prop instanceof AST_Number && expr instanceof AST_Array) {
            var index = prop.getValue();
            var elements = expr.elements;
            FLATTEN: if (index in elements) {
                var flatten = true;
                var values = [];
                for (var i = elements.length; --i > index;) {
                    var value = elements[i].drop_side_effect_free(compressor);
                    if (value) {
                        values.unshift(value);
                        if (flatten && value.has_side_effects(compressor)) flatten = false;
                    }
                }
                var retValue = elements[index];
                if (retValue instanceof AST_Expansion) break FLATTEN;
                retValue = retValue instanceof AST_Hole ? make_node(AST_Undefined, retValue) : retValue;
                if (!flatten) values.unshift(retValue);
                while (--i >= 0) {
                    var value = elements[i];
                    if (value instanceof AST_Expansion) break FLATTEN;
                    value = value.drop_side_effect_free(compressor);
                    if (value) values.unshift(value);
                    else index--;
                }
                if (flatten) {
                    values.push(retValue);
                    return make_sequence(self, values).optimize(compressor);
                } else return make_node(AST_Sub, self, {
                    expression: make_node(AST_Array, expr, {
                        elements: values
                    }),
                    property: make_node(AST_Number, prop, {
                        value: index
                    })
                });
            }
        }
        var ev = self.evaluate(compressor);
        if (ev !== self) {
            ev = make_node_from_constant(ev, self).optimize(compressor);
            return best_of(compressor, ev, self);
        }
        return self;
    });

    AST_Lambda.DEFMETHOD("contains_this", function() {
        var result;
        var self = this;
        self.walk(new TreeWalker(function(node) {
            if (result) return true;
            if (node instanceof AST_This) return result = true;
            if (node !== self && node instanceof AST_Scope && !(node instanceof AST_Arrow)) return true;
        }));
        return result;
    });

    AST_PropAccess.DEFMETHOD("flatten_object", function(key, compressor) {
        if (!compressor.option("properties")) return;
        var arrows = compressor.option("unsafe_arrows") && compressor.option("ecma") >= 6;
        var expr = this.expression;
        if (expr instanceof AST_Object) {
            var props = expr.properties;
            for (var i = props.length; --i >= 0;) {
                var prop = props[i];
                if ("" + (prop instanceof AST_ConciseMethod ? prop.key.name : prop.key) == key) {
                    if (!all(props, function(prop) {
                        return prop instanceof AST_ObjectKeyVal
                            || arrows && prop instanceof AST_ConciseMethod && !prop.is_generator;
                    })) break;
                    var value = prop.value;
                    if ((value instanceof AST_Accessor || value instanceof AST_Function)
                        && !(compressor.parent() instanceof AST_New)
                        && value.contains_this()) break;
                    return make_node(AST_Sub, this, {
                        expression: make_node(AST_Array, expr, {
                            elements: props.map(function(prop) {
                                var v = prop.value;
                                if (v instanceof AST_Accessor) v = make_node(AST_Function, v, v);
                                var k = prop.key;
                                if (k instanceof AST_Node && !(k instanceof AST_SymbolMethod)) {
                                    return make_sequence(prop, [ k, v ]);
                                }
                                return v;
                            })
                        }),
                        property: make_node(AST_Number, this, {
                            value: i
                        })
                    });
                }
            }
        }
    });

    OPT(AST_Dot, function(self, compressor){
        if (self.property == "arguments" || self.property == "caller") {
            compressor.warn("Function.protoype.{prop} not supported [{file}:{line},{col}]", {
                prop: self.property,
                file: self.start.file,
                line: self.start.line,
                col: self.start.col
            });
        }
        var def = self.resolve_defines(compressor);
        if (def) {
            return def.optimize(compressor);
        }
        if (is_lhs(self, compressor.parent())) return self;
        if (compressor.option("unsafe_proto")
            && self.expression instanceof AST_Dot
            && self.expression.property == "prototype") {
            var exp = self.expression.expression;
            if (is_undeclared_ref(exp)) switch (exp.name) {
              case "Array":
                self.expression = make_node(AST_Array, self.expression, {
                    elements: []
                });
                break;
              case "Function":
                self.expression = make_node(AST_Function, self.expression, {
                    argnames: [],
                    body: []
                });
                break;
              case "Number":
                self.expression = make_node(AST_Number, self.expression, {
                    value: 0
                });
                break;
              case "Object":
                self.expression = make_node(AST_Object, self.expression, {
                    properties: []
                });
                break;
              case "RegExp":
                self.expression = make_node(AST_RegExp, self.expression, {
                    value: /t/
                });
                break;
              case "String":
                self.expression = make_node(AST_String, self.expression, {
                    value: ""
                });
                break;
            }
        }
        var sub = self.flatten_object(self.property, compressor);
        if (sub) return sub.optimize(compressor);
        var ev = self.evaluate(compressor);
        if (ev !== self) {
            ev = make_node_from_constant(ev, self).optimize(compressor);
            return best_of(compressor, ev, self);
        }
        return self;
    });

    function literals_in_boolean_context(self, compressor) {
        if (compressor.in_boolean_context()) {
            return best_of(compressor, self, make_sequence(self, [
                self,
                make_node(AST_True, self)
            ]).optimize(compressor));
        }
        return self;
    };
    OPT(AST_Array, literals_in_boolean_context);
    OPT(AST_Object, literals_in_boolean_context);
    OPT(AST_RegExp, literals_in_boolean_context);

    OPT(AST_Return, function(self, compressor){
        if (self.value && is_undefined(self.value, compressor)) {
            self.value = null;
        }
        return self;
    });

    OPT(AST_Arrow, function(self, compressor){
        if (!(self.body instanceof AST_Node)) tighten_body(self.body, compressor);
        if (compressor.option("arrows")
            && self.body.length == 1
            && self.body[0] instanceof AST_Return) {
            var value = self.body[0].value;
            self.body = value ? value : [];
        }
        return self;
    });

    OPT(AST_Function, function(self, compressor){
        tighten_body(self.body, compressor);
        if (compressor.option("unsafe_arrows")
            && compressor.option("ecma") >= 6
            && !self.name
            && !self.is_generator
            && !self.uses_arguments
            && !self.uses_eval) {
            var has_special_symbol = false;
            self.walk(new TreeWalker(function(node) {
                if (has_special_symbol) return true;
                if (node instanceof AST_This) {
                    has_special_symbol = true;
                    return true;
                }
            }));
            if (!has_special_symbol) return make_node(AST_Arrow, self, self).optimize(compressor);
        }
        return self;
    });

    OPT(AST_Class, function(self, compressor){
        // HACK to avoid compress failure.
        // AST_Class is not really an AST_Scope/AST_Block as it lacks a body.
        return self;
    });

    OPT(AST_Yield, function(self, compressor){
        if (self.expression && !self.is_star && is_undefined(self.expression, compressor)) {
            self.expression = null;
        }
        return self;
    });

    OPT(AST_VarDef, function(self, compressor){
        var defines = compressor.option("global_defs");
        if (defines && HOP(defines, self.name.name)) {
            compressor.warn('global_defs ' + self.name.name + ' redefined [{file}:{line},{col}]', self.start);
        }
        return self;
    });

    OPT(AST_TemplateString, function(self, compressor){
        if (!compressor.option("evaluate")
        || compressor.parent() instanceof AST_PrefixedTemplateString)
            return self;

        var segments = [];
        for (var i = 0; i < self.segments.length; i++) {
            var segment = self.segments[i];
            if (segment instanceof AST_Node) {
                var result = segment.evaluate(compressor);
                // Evaluate to constant value
                // Constant value shorter than ${segment}
                if (result !== segment && (result + "").length <= segment.print_to_string().length + "${}".length) {
                    // There should always be a previous and next segment if segment is a node
                    segments[segments.length - 1].value = segments[segments.length - 1].value + result + self.segments[++i].value;
                    continue;
                }
            }
            segments.push(segment);
        }
        self.segments = segments;

        return segments.length == 1 ? make_node(AST_String, self, segments[0]) : self;
    });

    OPT(AST_PrefixedTemplateString, function(self, compressor){
        return self;
    });

    // ["p"]:1 ---> p:1
    // [42]:1 ---> 42:1
    function lift_key(self, compressor) {
        if (!compressor.option("computed_props")) return self;
        // save a comparison in the typical case
        if (!(self.key instanceof AST_Constant)) return self;
        // whitelist acceptable props as not all AST_Constants are true constants
        if (self.key instanceof AST_String || self.key instanceof AST_Number) {
            if (self.key.value == "constructor"
                && compressor.parent() instanceof AST_Class) return self;
            if (self instanceof AST_ObjectKeyVal) {
                self.key = self.key.value;
            } else {
                self.key = make_node(AST_SymbolMethod, self.key, {
                    name: self.key.value
                });
            }
        }
        return self;
    }

    OPT(AST_ObjectProperty, lift_key);

    OPT(AST_ConciseMethod, function(self, compressor){
        lift_key(self, compressor);
        // p(){return x;} ---> p:()=>x
        if (compressor.option("arrows")
            && compressor.parent() instanceof AST_Object
            && !self.value.uses_arguments
            && !self.value.uses_eval
            && self.value.body.length == 1
            && self.value.body[0] instanceof AST_Return
            && self.value.body[0].value
            && !self.value.contains_this()) {
            var arrow = make_node(AST_Arrow, self.value, self.value);
            arrow.async = self.async;
            arrow.is_generator = self.is_generator;
            return make_node(AST_ObjectKeyVal, self, {
                key: self.key instanceof AST_SymbolMethod ? self.key.name : self.key,
                value: arrow,
                quote: self.quote,
            });
        }
        return self;
    });

    OPT(AST_ObjectKeyVal, function(self, compressor){
        lift_key(self, compressor);
        // p:function(){} ---> p(){}
        // p:function*(){} ---> *p(){}
        // p:async function(){} ---> async p(){}
        // p:()=>{} ---> p(){}
        // p:async()=>{} ---> async p(){}
        var unsafe_methods = compressor.option("unsafe_methods");
        if (unsafe_methods
            && compressor.option("ecma") >= 6
            && (!(unsafe_methods instanceof RegExp) || unsafe_methods.test(self.key + ""))) {
            var key = self.key;
            var value = self.value;
            var is_arrow_with_block = value instanceof AST_Arrow
                && Array.isArray(value.body)
                && !value.contains_this();
            if ((is_arrow_with_block || value instanceof AST_Function) && !value.name) {
                return make_node(AST_ConciseMethod, self, {
                    async: value.async,
                    is_generator: value.is_generator,
                    key: key instanceof AST_Node ? key : make_node(AST_SymbolMethod, self, {
                        name: key,
                    }),
                    value: make_node(AST_Accessor, value, value),
                    quote: self.quote,
                });
            }
        }
        return self;
    });
})();
