v3.0.15

fixes #2040

README.md

@@ -45,6 +45,7 @@ a double dash to prevent input files being used as option arguments:
 
 ```
     -h, --help                  Print usage information.
+                                `--help options` for details on available options.
     -V, --version               Print version number.
     -p, --parse <options>       Specify parser options:
                                 `acorn`  Use Acorn for parsing.
@@ -571,6 +572,8 @@ If you're using the `X-SourceMap` header instead, you can just omit `sourceMap.u
   comparison are switching. Compression only works if both `comparisons` and
   `unsafe_comps` are both set to true.
 
+- `unsafe_Func` (default: false) -- compress and mangle `Function(args, code)`.
+
 - `unsafe_math` (default: false) -- optimize numerical expressions like
   `2 * x * 3` into `6 * x`, which may give imprecise floating point results.
 
@@ -677,17 +680,18 @@ If you're using the `X-SourceMap` header instead, you can just omit `sourceMap.u
 
 ## Mangle options
 
-- `reserved` - pass an array of identifiers that should be excluded from mangling
+- `reserved` (default `[]`). Pass an array of identifiers that should be
+  excluded from mangling. Example: `["foo", "bar"]`.
 
-- `toplevel` — mangle names declared in the top level scope (disabled by
-default).
+- `toplevel` (default `false`). Pass `true` to mangle names declared in the
+  top level scope.
 
-- `eval` — mangle names visible in scopes where eval or with are used
-(disabled by default).
+- `keep_fnames` (default `false`).  Pass `true` to not mangle function names.
+  Useful for code relying on `Function.prototype.name`. See also: the `keep_fnames`
+  [compress option](#compress-options).
 
-- `keep_fnames` -- default `false`.  Pass `true` to not mangle
-function names.  Useful for code relying on `Function.prototype.name`.
-See also: the `keep_fnames` [compress option](#compress-options).
+- `eval` (default `false`). Pass `true` to mangle names visible in scopes
+  where `eval` or `with` are used.
 
 Examples:
 

bin/uglifyjs

@@ -21,10 +21,27 @@ var options = {
     compress: false,
     mangle: false
 };
-program.version(info.name + ' ' + info.version);
+program.version(info.name + " " + info.version);
 program.parseArgv = program.parse;
 program.parse = undefined;
 if (process.argv.indexOf("ast") >= 0) program.helpInformation = UglifyJS.describe_ast;
+else if (process.argv.indexOf("options") >= 0) program.helpInformation = function() {
+    var text = [];
+    var options = UglifyJS.default_options();
+    for (var option in options) {
+        text.push("--" + (option == "output" ? "beautify" : option == "sourceMap" ? "source-map" : option) + " options:");
+        var defs = options[option];
+        var padding = "";
+        Object.keys(defs).map(function(name) {
+            if (padding.length < name.length) padding = Array(name.length + 1).join(" ");
+            return [ name, JSON.stringify(defs[name]) ];
+        }).forEach(function(tokens) {
+            text.push("  " + tokens[0] + padding.slice(tokens[0].length - 2) + tokens[1]);
+        });
+        text.push("");
+    }
+    return text.join("\n");
+};
 program.option("-p, --parse <options>", "Specify parser options.", parse_js("parse", true));
 program.option("-c, --compress [options]", "Enable compressor/specify compressor options.", parse_js("compress", true));
 program.option("-m, --mangle [options]", "Mangle names/specify mangler options.", parse_js("mangle", true));
@@ -208,9 +225,10 @@ function run() {
                 col = line.length;
             }
             if (line) {
-                if (col > 40) {
-                    line = line.slice(col - 40);
-                    col = 40;
+                var limit = 70;
+                if (col > limit) {
+                    line = line.slice(col - limit);
+                    col = limit;
                 }
                 console.error(line.slice(0, 80));
                 console.error(line.slice(0, col).replace(/\S/g, " ") + "^");
@@ -351,7 +369,7 @@ function parse_js(flag, constants) {
                 }
             }));
         } catch(ex) {
-            fatal("Error parsing arguments for '" + flag + "': " + value);
+            options[value] = null;
         }
         return options;
     }

lib/compress.js

@@ -81,6 +81,7 @@ function Compressor(options, false_by_default) {
         toplevel      : !!(options && options["top_retain"]),
         unsafe        : false,
         unsafe_comps  : false,
+        unsafe_Func   : false,
         unsafe_math   : false,
         unsafe_proto  : false,
         unsafe_regexp : false,
@@ -924,6 +925,45 @@ merge(Compressor.prototype, {
                     // step.  nevertheless, it's good to check.
                     continue loop;
                   case 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;
+                        var funs = extract_functions_from_statement_array(ret);
+                        var body = as_statement_array_with_return(stat.body, ab);
+                        stat = stat.clone();
+                        stat.condition = stat.condition.negate(compressor);
+                        stat.body = make_node(AST_BlockStatement, stat, {
+                            body: as_statement_array(stat.alternative).concat(ret)
+                        });
+                        stat.alternative = make_node(AST_BlockStatement, stat, {
+                            body: body
+                        });
+                        ret = [ stat.transform(compressor) ].concat(funs);
+                        continue loop;
+                    }
+
+                    var ab = aborts(stat.alternative);
+                    if (can_merge_flow(ab)) {
+                        if (ab.label) {
+                            remove(ab.label.thedef.references, ab);
+                        }
+                        CHANGED = true;
+                        var funs = extract_functions_from_statement_array(ret);
+                        stat = stat.clone();
+                        stat.body = make_node(AST_BlockStatement, stat.body, {
+                            body: as_statement_array(stat.body).concat(ret)
+                        });
+                        var body = as_statement_array_with_return(stat.alternative, ab);
+                        stat.alternative = make_node(AST_BlockStatement, stat.alternative, {
+                            body: body
+                        });
+                        ret = [ stat.transform(compressor) ].concat(funs);
+                        continue loop;
+                    }
+
                     if (stat.body instanceof AST_Return) {
                         var value = stat.body.value;
                         //---
@@ -960,23 +1000,6 @@ merge(Compressor.prototype, {
                             continue loop;
                         }
                         //---
-                        // if (foo()) return [ void bar() ]; [ else x...; ] y... ==> if (!foo()) { x...; y... } else bar();
-                        if (in_lambda && (!value || value instanceof AST_UnaryPrefix && value.operator == "void")) {
-                            CHANGED = true;
-                            stat = stat.clone();
-                            stat.condition = stat.condition.negate(compressor);
-                            var funs = extract_functions_from_statement_array(ret);
-                            var body = as_statement_array(stat.alternative).concat(ret);
-                            stat.body = make_node(AST_BlockStatement, stat, {
-                                body: body
-                            });
-                            stat.alternative = value ? make_node(AST_SimpleStatement, value, {
-                                body: value.expression
-                            }) : null;
-                            ret = [ stat.transform(compressor) ].concat(funs);
-                            continue loop;
-                        }
-                        //---
                         // 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).
@@ -995,48 +1018,6 @@ merge(Compressor.prototype, {
                         }
                     }
 
-                    var ab = aborts(stat.body);
-                    var lct = ab instanceof AST_LoopControl ? compressor.loopcontrol_target(ab) : null;
-                    if (ab && ((ab instanceof AST_Return && !ab.value && in_lambda)
-                               || (ab instanceof AST_Continue && self === loop_body(lct))
-                               || (ab instanceof AST_Break && lct instanceof AST_BlockStatement && self === lct))) {
-                        if (ab.label) {
-                            remove(ab.label.thedef.references, ab);
-                        }
-                        CHANGED = true;
-                        var body = as_statement_array(stat.body).slice(0, -1);
-                        stat = stat.clone();
-                        stat.condition = stat.condition.negate(compressor);
-                        stat.body = make_node(AST_BlockStatement, stat, {
-                            body: as_statement_array(stat.alternative).concat(ret)
-                        });
-                        stat.alternative = make_node(AST_BlockStatement, stat, {
-                            body: body
-                        });
-                        ret = [ stat.transform(compressor) ];
-                        continue loop;
-                    }
-
-                    var ab = aborts(stat.alternative);
-                    var lct = ab instanceof AST_LoopControl ? compressor.loopcontrol_target(ab) : null;
-                    if (ab && ((ab instanceof AST_Return && !ab.value && in_lambda)
-                               || (ab instanceof AST_Continue && self === loop_body(lct))
-                               || (ab instanceof AST_Break && lct instanceof AST_BlockStatement && self === lct))) {
-                        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(ret)
-                        });
-                        stat.alternative = make_node(AST_BlockStatement, stat.alternative, {
-                            body: as_statement_array(stat.alternative).slice(0, -1)
-                        });
-                        ret = [ stat.transform(compressor) ];
-                        continue loop;
-                    }
-
                     ret.unshift(stat);
                     break;
                   default:
@@ -1056,6 +1037,28 @@ merge(Compressor.prototype, {
                 }
                 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;
+                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 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 eliminate_dead_code(statements, compressor) {
@@ -1662,6 +1665,63 @@ merge(Compressor.prototype, {
             }
             throw def;
         });
+        var object_fns = [
+            'constructor',
+            'toString',
+            'valueOf',
+        ];
+        var native_fns = {
+            Array: makePredicate([
+                'indexOf',
+                'join',
+                'lastIndexOf',
+                'slice',
+            ].concat(object_fns)),
+            Boolean: makePredicate(object_fns),
+            Number: makePredicate([
+                'toExponential',
+                'toFixed',
+                'toPrecision',
+            ].concat(object_fns)),
+            RegExp: makePredicate([
+                'test',
+            ].concat(object_fns)),
+            String: makePredicate([
+                'charAt',
+                'charCodeAt',
+                'concat',
+                'indexOf',
+                'italics',
+                'lastIndexOf',
+                'match',
+                'replace',
+                'search',
+                'slice',
+                'split',
+                'substr',
+                'substring',
+                'trim',
+            ].concat(object_fns)),
+        };
+        def(AST_Call, function(compressor){
+            var exp = this.expression;
+            if (compressor.option("unsafe") && exp instanceof AST_PropAccess) {
+                var key = exp.property;
+                if (key instanceof AST_Node) {
+                    key = ev(key, compressor);
+                }
+                var val = ev(exp.expression, compressor);
+                if ((val && native_fns[val.constructor.name] || return_false)(key)) {
+                    return val[key].apply(val, this.args.map(function(arg) {
+                        return ev(arg, compressor);
+                    }));
+                }
+            }
+            throw def;
+        });
+        def(AST_New, function(compressor){
+            throw def;
+        });
     })(function(node, func){
         node.DEFMETHOD("_eval", func);
     });
@@ -2971,63 +3031,6 @@ merge(Compressor.prototype, {
                         operator: "!"
                     }).optimize(compressor);
                     break;
-                  case "Function":
-                    // new Function() => function(){}
-                    if (self.args.length == 0) return make_node(AST_Function, self, {
-                        argnames: [],
-                        body: []
-                    });
-                    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 = "(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);
-                            ast.mangle_names();
-                            var fun;
-                            try {
-                                ast.walk(new TreeWalker(function(node){
-                                    if (node instanceof AST_Lambda) {
-                                        fun = node;
-                                        throw ast;
-                                    }
-                                }));
-                            } catch(ex) {
-                                if (ex !== ast) throw ex;
-                            };
-                            if (!fun) return self;
-                            var args = fun.argnames.map(function(arg, i){
-                                return make_node(AST_String, self.args[i], {
-                                    value: arg.print_to_string()
-                                });
-                            });
-                            var code = OutputStream();
-                            AST_BlockStatement.prototype._codegen.call(fun, fun, code);
-                            code = code.toString().replace(/^\{|\}$/g, "");
-                            args.push(make_node(AST_String, self.args[self.args.length - 1], {
-                                value: code
-                            }));
-                            self.args = args;
-                            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 {
-                                console.log(ex);
-                                throw ex;
-                            }
-                        }
-                    }
-                    break;
                 }
             }
             else if (exp instanceof AST_Dot && exp.property == "toString" && self.args.length == 0) {
@@ -3110,6 +3113,63 @@ merge(Compressor.prototype, {
                 }
             }
         }
+        if (compressor.option("unsafe_Func")
+            && exp instanceof AST_SymbolRef
+            && exp.undeclared()
+            && exp.name == "Function") {
+            // new Function() => function(){}
+            if (self.args.length == 0) return make_node(AST_Function, self, {
+                argnames: [],
+                body: []
+            });
+            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 = "NaN(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);
+                    ast.mangle_names();
+                    var fun;
+                    ast.walk(new TreeWalker(function(node) {
+                        if (fun) return true;
+                        if (node instanceof AST_Lambda) {
+                            fun = node;
+                            return true;
+                        }
+                    }));
+                    var args = fun.argnames.map(function(arg, i) {
+                        return make_node(AST_String, self.args[i], {
+                            value: arg.print_to_string()
+                        });
+                    });
+                    var code = OutputStream();
+                    AST_BlockStatement.prototype._codegen.call(fun, fun, code);
+                    code = code.toString().replace(/^\{|\}$/g, "");
+                    args.push(make_node(AST_String, self.args[self.args.length - 1], {
+                        value: code
+                    }));
+                    self.args = args;
+                    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;
+                    }
+                }
+            }
+        }
         if (exp instanceof AST_Function) {
             if (exp.body[0] instanceof AST_Return) {
                 var value = exp.body[0].value;
@@ -3141,6 +3201,11 @@ merge(Compressor.prototype, {
             && 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;
     });
 

lib/output.js

@@ -1234,9 +1234,8 @@ function OutputStream(options) {
         });
         else output.print("{}");
     });
-    DEFPRINT(AST_ObjectKeyVal, function(self, output){
-        var key = self.key;
-        var quote = self.quote;
+
+    function print_property_name(key, quote, output) {
         if (output.option("quote_keys")) {
             output.print_string(key + "");
         } else if ((typeof key == "number"
@@ -1253,20 +1252,24 @@ function OutputStream(options) {
         } else {
             output.print_string(key, quote);
         }
+    }
+
+    DEFPRINT(AST_ObjectKeyVal, function(self, output){
+        print_property_name(self.key, self.quote, output);
         output.colon();
         self.value.print(output);
     });
-    DEFPRINT(AST_ObjectSetter, function(self, output){
-        output.print("set");
+    AST_ObjectProperty.DEFMETHOD("_print_getter_setter", function(type, output) {
+        output.print(type);
         output.space();
-        self.key.print(output);
-        self.value._do_print(output, true);
+        print_property_name(this.key.name, this.quote, output);
+        this.value._do_print(output, true);
+    });
+    DEFPRINT(AST_ObjectSetter, function(self, output){
+        self._print_getter_setter("set", output);
     });
     DEFPRINT(AST_ObjectGetter, function(self, output){
-        output.print("get");
-        output.space();
-        self.key.print(output);
-        self.value._do_print(output, true);
+        self._print_getter_setter("get", output);
     });
     DEFPRINT(AST_Symbol, function(self, output){
         var def = self.definition();

lib/parse.js

@@ -700,7 +700,7 @@ function parse($TEXT, options) {
         shebang        : true,
         strict         : false,
         toplevel       : null,
-    });
+    }, true);
 
     var S = {
         input         : (typeof $TEXT == "string"

package.json

@@ -4,7 +4,7 @@
   "homepage": "http://lisperator.net/uglifyjs",
   "author": "Mihai Bazon <mihai.bazon@gmail.com> (http://lisperator.net/)",
   "license": "BSD-2-Clause",
-  "version": "3.0.12",
+  "version": "3.0.15",
   "engines": {
     "node": ">=0.8.0"
   },

test/compress/dead-code.js

@@ -99,7 +99,7 @@ dead_code_2_should_warn_strict: {
         f();
     }
     expect_stdout: true
-    node_version: "=4"
+    node_version: ">=4"
 }
 
 dead_code_constant_boolean_should_warn_more: {

test/compress/evaluate.js

@@ -780,13 +780,15 @@ unsafe_charAt_noop: {
     input: {
         console.log(
             s.charAt(0),
-            "string".charAt(x)
+            "string".charAt(x),
+            (typeof x).charAt()
         );
     }
     expect: {
         console.log(
             s.charAt(0),
-            "string".charAt(x)
+            "string".charAt(x),
+            (typeof x)[0]
         );
     }
 }
@@ -1037,3 +1039,31 @@ issue_1964_2: {
     }
     expect_stdout: "b"
 }
+
+array_slice_index: {
+    options = {
+        evaluate: true,
+        unsafe: true,
+    }
+    input: {
+        console.log([1,2,3].slice(1)[1]);
+    }
+    expect: {
+        console.log(3);
+    }
+    expect_stdout: "3"
+}
+
+string_charCodeAt: {
+    options = {
+        evaluate: true,
+        unsafe: true,
+    }
+    input: {
+        console.log("foo".charCodeAt("bar".length));
+    }
+    expect: {
+        console.log(NaN);
+    }
+    expect_stdout: "NaN"
+}

test/compress/functions.js

@@ -243,5 +243,27 @@ hoist_funs_strict: {
         "5 'function' 'function'",
         "6 'undefined' 'function'",
     ]
-    node_version: "=4"
+    node_version: ">=4"
+}
+
+issue_203: {
+    options = {
+        keep_fargs: false,
+        side_effects: true,
+        unsafe_Func: true,
+        unused: true,
+    }
+    input: {
+        var m = {};
+        var fn = Function("require", "module", "exports", "module.exports = 42;");
+        fn(null, m, m.exports);
+        console.log(m.exports);
+    }
+    expect: {
+        var m = {};
+        var fn = Function("a", "b", "b.exports=42");
+        fn(null, m, m.exports);
+        console.log(m.exports);
+    }
+    expect_stdout: "42"
 }

test/compress/if_return.js

@@ -307,6 +307,8 @@ issue_512: {
     options = {
         conditionals: true,
         if_return: true,
+        sequences: true,
+        side_effects: true,
     }
     input: {
         function a() {

test/compress/issue-1052.js

@@ -136,7 +136,29 @@ defun_hoist_funs: {
             function f() {}
             function g() {}
             function h() {}
-            !window;
+            if (window);
+        }
+    }
+}
+
+defun_else_if_return: {
+    options = {
+        hoist_funs: false,
+        if_return: true,
+    }
+    input: {
+        function e() {
+            function f() {}
+            if (window) function g() {}
+            else return;
+            function h() {}
+        }
+    }
+    expect: {
+        function e() {
+            function f() {}
+            if (window) function g() {}
+            function h() {}
         }
     }
 }

test/compress/properties.js

@@ -555,3 +555,20 @@ native_prototype: {
         "".indexOf.call(e, "bar");
     }
 }
+
+issue_2040: {
+    input: {
+        var a = 1;
+        var b = {
+            get "a-b"() {
+                return a;
+            },
+            set "a-b"(c) {
+                a = c;
+            }
+        };
+        console.log(b["a-b"], b["a-b"] = 2, b["a-b"]);
+    }
+    expect_exact: 'var a=1;var b={get"a-b"(){return a},set"a-b"(c){a=c}};console.log(b["a-b"],b["a-b"]=2,b["a-b"]);'
+    expect_stdout: "1 2 2"
+}

test/mocha/cli.js

@@ -537,4 +537,13 @@ describe("bin/uglifyjs", function () {
             done();
         });
     });
+    it("Should print supported options on invalid option syntax", function(done) {
+        var command = uglifyjscmd + " test/input/comments/filter.js -b ascii-only";
+        exec(command, function (err, stdout, stderr) {
+            assert.ok(err);
+            assert.strictEqual(stdout, "");
+            assert.ok(/^Supported options:\n\{[^}]+}\nERROR: `ascii-only` is not a supported option/.test(stderr), stderr);
+            done();
+        });
+    });
 });

test/ufuzz.js

@@ -12,7 +12,7 @@
         stream._handle.setBlocking(true);
 });
 
-var UglifyJS = require("./node");
+var UglifyJS = require("..");
 var randomBytes = require("crypto").randomBytes;
 var sandbox = require("./sandbox");
 
@@ -962,32 +962,15 @@ function try_beautify(code, result) {
     console.log(code);
 }
 
-function infer_options(ctor) {
-    try {
-        ctor({ 0: 0 });
-    } catch (e) {
-        return e.defs;
-    }
-}
-
-var default_options = {
-    compress: infer_options(UglifyJS.Compressor),
-    mangle: {
-        "cache": null,
-        "eval": false,
-        "ie8": false,
-        "keep_fnames": false,
-        "toplevel": false,
-    },
-    output: infer_options(UglifyJS.OutputStream),
-};
+var default_options = UglifyJS.default_options();
 
 function log_suspects(minify_options, component) {
     var options = component in minify_options ? minify_options[component] : true;
     if (!options) return;
-    options = UglifyJS.defaults(options, default_options[component]);
-    var suspects = Object.keys(default_options[component]).filter(function(name) {
-        if (options[name]) {
+    if (typeof options != "object") options = {};
+    var defs = default_options[component];
+    var suspects = Object.keys(defs).filter(function(name) {
+        if ((name in options ? options : defs)[name]) {
             var m = JSON.parse(JSON.stringify(minify_options));
             var o = JSON.parse(JSON.stringify(options));
             o[name] = false;

tools/node.js

@@ -63,3 +63,20 @@ function describe_ast() {
     doitem(AST_Node);
     return out + "\n";
 }
+
+function infer_options(options) {
+    var result = UglifyJS.minify("", options);
+    return result.error && result.error.defs;
+}
+
+UglifyJS.default_options = function() {
+    var defs = {};
+    Object.keys(infer_options({ 0: 0 })).forEach(function(component) {
+        var options = {};
+        options[component] = { 0: 0 };
+        if (options = infer_options(options)) {
+            defs[component] = options;
+        }
+    });
+    return defs;
+};