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diff --git a/node_modules/uglify-js/README.md b/node_modules/uglify-js/README.md new file mode 100644 index 00000000..a08a36df --- /dev/null +++ b/node_modules/uglify-js/README.md @@ -0,0 +1,1135 @@ +UglifyJS 3 +========== + +UglifyJS is a JavaScript parser, minifier, compressor and beautifier toolkit. + +#### Note: +- **`uglify-js@3` has a simplified [API](#api-reference) and [CLI](#command-line-usage) that is not backwards compatible with [`uglify-js@2`](https://github.com/mishoo/UglifyJS2/tree/v2.x)**. +- **Documentation for UglifyJS `2.x` releases can be found [here](https://github.com/mishoo/UglifyJS2/tree/v2.x)**. +- `uglify-js` only supports JavaScript (ECMAScript 5). +- To minify ECMAScript 2015 or above, transpile using tools like [Babel](https://babeljs.io/). + +Install +------- + +First make sure you have installed the latest version of [node.js](http://nodejs.org/) +(You may need to restart your computer after this step). + +From NPM for use as a command line app: + + npm install uglify-js -g + +From NPM for programmatic use: + + npm install uglify-js + +# Command line usage + + uglifyjs [input files] [options] + +UglifyJS can take multiple input files. It's recommended that you pass the +input files first, then pass the options. UglifyJS will parse input files +in sequence and apply any compression options. The files are parsed in the +same global scope, that is, a reference from a file to some +variable/function declared in another file will be matched properly. + +If no input file is specified, UglifyJS will read from STDIN. + +If you wish to pass your options before the input files, separate the two with +a double dash to prevent input files being used as option arguments: + + uglifyjs --compress --mangle -- input.js + +### Command line options + +``` + -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. + `bare_returns` Allow return outside of functions. + Useful when minifying CommonJS + modules and Userscripts that may + be anonymous function wrapped (IIFE) + by the .user.js engine `caller`. + `expression` Parse a single expression, rather than + a program (for parsing JSON). + `spidermonkey` Assume input files are SpiderMonkey + AST format (as JSON). + -c, --compress [options] Enable compressor/specify compressor options: + `pure_funcs` List of functions that can be safely + removed when their return values are + not used. + -m, --mangle [options] Mangle names/specify mangler options: + `reserved` List of names that should not be mangled. + --mangle-props [options] Mangle properties/specify mangler options: + `builtins` Mangle property names that overlaps + with standard JavaScript globals. + `debug` Add debug prefix and suffix. + `domprops` Mangle property names that overlaps + with DOM properties. + `keep_quoted` Only mangle unquoted properties. + `regex` Only mangle matched property names. + `reserved` List of names that should not be mangled. + -b, --beautify [options] Beautify output/specify output options: + `beautify` Enabled with `--beautify` by default. + `preamble` Preamble to prepend to the output. You + can use this to insert a comment, for + example for licensing information. + This will not be parsed, but the source + map will adjust for its presence. + `quote_style` Quote style: + 0 - auto + 1 - single + 2 - double + 3 - original + `wrap_iife` Wrap IIFEs in parenthesis. Note: you may + want to disable `negate_iife` under + compressor options. + -o, --output <file> Output file path (default STDOUT). Specify `ast` or + `spidermonkey` to write UglifyJS or SpiderMonkey AST + as JSON to STDOUT respectively. + --comments [filter] Preserve copyright comments in the output. By + default this works like Google Closure, keeping + JSDoc-style comments that contain "@license" or + "@preserve". You can optionally pass one of the + following arguments to this flag: + - "all" to keep all comments + - a valid JS RegExp like `/foo/` or `/^!/` to + keep only matching comments. + Note that currently not *all* comments can be + kept when compression is on, because of dead + code removal or cascading statements into + sequences. + --config-file <file> Read `minify()` options from JSON file. + -d, --define <expr>[=value] Global definitions. + -e, --enclose [arg[:value]] Embed everything in a big function, with configurable + argument(s) & value(s). + --ie8 Support non-standard Internet Explorer 8. + Equivalent to setting `ie8: true` in `minify()` + for `compress`, `mangle` and `output` options. + By default UglifyJS will not try to be IE-proof. + --keep-fnames Do not mangle/drop function names. Useful for + code relying on Function.prototype.name. + --name-cache <file> File to hold mangled name mappings. + --self Build UglifyJS as a library (implies --wrap UglifyJS) + --source-map [options] Enable source map/specify source map options: + `base` Path to compute relative paths from input files. + `content` Input source map, useful if you're compressing + JS that was generated from some other original + code. Specify "inline" if the source map is + included within the sources. + `filename` Filename and/or location of the output source + (sets `file` attribute in source map). + `includeSources` Pass this flag if you want to include + the content of source files in the + source map as sourcesContent property. + `root` Path to the original source to be included in + the source map. + `url` If specified, path to the source map to append in + `//# sourceMappingURL`. + --timings Display operations run time on STDERR. + --toplevel Compress and/or mangle variables in top level scope. + --verbose Print diagnostic messages. + --warn Print warning messages. + --wrap <name> Embed everything in a big function, making the + “exports” and “global” variables available. You + need to pass an argument to this option to + specify the name that your module will take + when included in, say, a browser. +``` + +Specify `--output` (`-o`) to declare the output file. Otherwise the output +goes to STDOUT. + +## CLI source map options + +UglifyJS can generate a source map file, which is highly useful for +debugging your compressed JavaScript. To get a source map, pass +`--source-map --output output.js` (source map will be written out to +`output.js.map`). + +Additional options: + +- `--source-map "filename='<NAME>'"` to specify the name of the source map. The value of + `filename` is only used to set `file` attribute (see [the spec][sm-spec]) + in source map file. + +- `--source-map "root='<URL>'"` to pass the URL where the original files can be found. + +- `--source-map "url='<URL>'"` to specify the URL where the source map can be found. + Otherwise UglifyJS assumes HTTP `X-SourceMap` is being used and will omit the + `//# sourceMappingURL=` directive. + +For example: + + uglifyjs js/file1.js js/file2.js \ + -o foo.min.js -c -m \ + --source-map "root='http://foo.com/src',url='foo.min.js.map'" + +The above will compress and mangle `file1.js` and `file2.js`, will drop the +output in `foo.min.js` and the source map in `foo.min.js.map`. The source +mapping will refer to `http://foo.com/src/js/file1.js` and +`http://foo.com/src/js/file2.js` (in fact it will list `http://foo.com/src` +as the source map root, and the original files as `js/file1.js` and +`js/file2.js`). + +### Composed source map + +When you're compressing JS code that was output by a compiler such as +CoffeeScript, mapping to the JS code won't be too helpful. Instead, you'd +like to map back to the original code (i.e. CoffeeScript). UglifyJS has an +option to take an input source map. Assuming you have a mapping from +CoffeeScript → compiled JS, UglifyJS can generate a map from CoffeeScript → +compressed JS by mapping every token in the compiled JS to its original +location. + +To use this feature pass `--source-map "content='/path/to/input/source.map'"` +or `--source-map "content=inline"` if the source map is included inline with +the sources. + +## CLI compress options + +You need to pass `--compress` (`-c`) to enable the compressor. Optionally +you can pass a comma-separated list of [compress options](#compress-options). + +Options are in the form `foo=bar`, or just `foo` (the latter implies +a boolean option that you want to set `true`; it's effectively a +shortcut for `foo=true`). + +Example: + + uglifyjs file.js -c toplevel,sequences=false + +## CLI mangle options + +To enable the mangler you need to pass `--mangle` (`-m`). The following +(comma-separated) options are supported: + +- `toplevel` (default `false`) -- mangle names declared in the top level scope. + +- `eval` (default `false`) -- mangle names visible in scopes where `eval` or `with` are used. + +When mangling is enabled but you want to prevent certain names from being +mangled, you can declare those names with `--mangle reserved` — pass a +comma-separated list of names. For example: + + uglifyjs ... -m reserved=['$','require','exports'] + +to prevent the `require`, `exports` and `$` names from being changed. + +### CLI mangling property names (`--mangle-props`) + +**Note:** THIS WILL PROBABLY BREAK YOUR CODE. Mangling property names +is a separate step, different from variable name mangling. Pass +`--mangle-props` to enable it. It will mangle all properties in the +input code with the exception of built in DOM properties and properties +in core JavaScript classes. For example: + +```javascript +// example.js +var x = { + baz_: 0, + foo_: 1, + calc: function() { + return this.foo_ + this.baz_; + } +}; +x.bar_ = 2; +x["baz_"] = 3; +console.log(x.calc()); +``` +Mangle all properties (except for JavaScript `builtins`): +```bash +$ uglifyjs example.js -c -m --mangle-props +``` +```javascript +var x={o:0,_:1,l:function(){return this._+this.o}};x.t=2,x.o=3,console.log(x.l()); +``` +Mangle all properties except for `reserved` properties: +```bash +$ uglifyjs example.js -c -m --mangle-props reserved=[foo_,bar_] +``` +```javascript +var x={o:0,foo_:1,_:function(){return this.foo_+this.o}};x.bar_=2,x.o=3,console.log(x._()); +``` +Mangle all properties matching a `regex`: +```bash +$ uglifyjs example.js -c -m --mangle-props regex=/_$/ +``` +```javascript +var x={o:0,_:1,calc:function(){return this._+this.o}};x.l=2,x.o=3,console.log(x.calc()); +``` + +Combining mangle properties options: +```bash +$ uglifyjs example.js -c -m --mangle-props regex=/_$/,reserved=[bar_] +``` +```javascript +var x={o:0,_:1,calc:function(){return this._+this.o}};x.bar_=2,x.o=3,console.log(x.calc()); +``` + +In order for this to be of any use, we avoid mangling standard JS names by +default (`--mangle-props builtins` to override). + +A default exclusion file is provided in `tools/domprops.json` which should +cover most standard JS and DOM properties defined in various browsers. Pass +`--mangle-props domprops` to disable this feature. + +A regular expression can be used to define which property names should be +mangled. For example, `--mangle-props regex=/^_/` will only mangle property +names that start with an underscore. + +When you compress multiple files using this option, in order for them to +work together in the end we need to ensure somehow that one property gets +mangled to the same name in all of them. For this, pass `--name-cache filename.json` +and UglifyJS will maintain these mappings in a file which can then be reused. +It should be initially empty. Example: + +```bash +$ rm -f /tmp/cache.json # start fresh +$ uglifyjs file1.js file2.js --mangle-props --name-cache /tmp/cache.json -o part1.js +$ uglifyjs file3.js file4.js --mangle-props --name-cache /tmp/cache.json -o part2.js +``` + +Now, `part1.js` and `part2.js` will be consistent with each other in terms +of mangled property names. + +Using the name cache is not necessary if you compress all your files in a +single call to UglifyJS. + +### Mangling unquoted names (`--mangle-props keep_quoted`) + +Using quoted property name (`o["foo"]`) reserves the property name (`foo`) +so that it is not mangled throughout the entire script even when used in an +unquoted style (`o.foo`). Example: + +```javascript +// stuff.js +var o = { + "foo": 1, + bar: 3 +}; +o.foo += o.bar; +console.log(o.foo); +``` +```bash +$ uglifyjs stuff.js --mangle-props keep_quoted -c -m +``` +```javascript +var o={foo:1,o:3};o.foo+=o.o,console.log(o.foo); +``` + +### Debugging property name mangling + +You can also pass `--mangle-props debug` in order to mangle property names +without completely obscuring them. For example the property `o.foo` +would mangle to `o._$foo$_` with this option. This allows property mangling +of a large codebase while still being able to debug the code and identify +where mangling is breaking things. + +```bash +$ uglifyjs stuff.js --mangle-props debug -c -m +``` +```javascript +var o={_$foo$_:1,_$bar$_:3};o._$foo$_+=o._$bar$_,console.log(o._$foo$_); +``` + +You can also pass a custom suffix using `--mangle-props debug=XYZ`. This would then +mangle `o.foo` to `o._$foo$XYZ_`. You can change this each time you compile a +script to identify how a property got mangled. One technique is to pass a +random number on every compile to simulate mangling changing with different +inputs (e.g. as you update the input script with new properties), and to help +identify mistakes like writing mangled keys to storage. + + +# API Reference + +Assuming installation via NPM, you can load UglifyJS in your application +like this: +```javascript +var UglifyJS = require("uglify-js"); +``` + +There is a single high level function, **`minify(code, options)`**, +which will perform all minification [phases](#minify-options) in a configurable +manner. By default `minify()` will enable the options [`compress`](#compress-options) +and [`mangle`](#mangle-options). Example: +```javascript +var code = "function add(first, second) { return first + second; }"; +var result = UglifyJS.minify(code); +console.log(result.error); // runtime error, or `undefined` if no error +console.log(result.code); // minified output: function add(n,d){return n+d} +``` + +You can `minify` more than one JavaScript file at a time by using an object +for the first argument where the keys are file names and the values are source +code: +```javascript +var code = { + "file1.js": "function add(first, second) { return first + second; }", + "file2.js": "console.log(add(1 + 2, 3 + 4));" +}; +var result = UglifyJS.minify(code); +console.log(result.code); +// function add(d,n){return d+n}console.log(add(3,7)); +``` + +The `toplevel` option: +```javascript +var code = { + "file1.js": "function add(first, second) { return first + second; }", + "file2.js": "console.log(add(1 + 2, 3 + 4));" +}; +var options = { toplevel: true }; +var result = UglifyJS.minify(code, options); +console.log(result.code); +// console.log(3+7); +``` + +The `nameCache` option: +```javascript +var options = { + mangle: { + toplevel: true, + }, + nameCache: {} +}; +var result1 = UglifyJS.minify({ + "file1.js": "function add(first, second) { return first + second; }" +}, options); +var result2 = UglifyJS.minify({ + "file2.js": "console.log(add(1 + 2, 3 + 4));" +}, options); +console.log(result1.code); +// function n(n,r){return n+r} +console.log(result2.code); +// console.log(n(3,7)); +``` + +You may persist the name cache to the file system in the following way: +```javascript +var cacheFileName = "/tmp/cache.json"; +var options = { + mangle: { + properties: true, + }, + nameCache: JSON.parse(fs.readFileSync(cacheFileName, "utf8")) +}; +fs.writeFileSync("part1.js", UglifyJS.minify({ + "file1.js": fs.readFileSync("file1.js", "utf8"), + "file2.js": fs.readFileSync("file2.js", "utf8") +}, options).code, "utf8"); +fs.writeFileSync("part2.js", UglifyJS.minify({ + "file3.js": fs.readFileSync("file3.js", "utf8"), + "file4.js": fs.readFileSync("file4.js", "utf8") +}, options).code, "utf8"); +fs.writeFileSync(cacheFileName, JSON.stringify(options.nameCache), "utf8"); +``` + +An example of a combination of `minify()` options: +```javascript +var code = { + "file1.js": "function add(first, second) { return first + second; }", + "file2.js": "console.log(add(1 + 2, 3 + 4));" +}; +var options = { + toplevel: true, + compress: { + global_defs: { + "@console.log": "alert" + }, + passes: 2 + }, + output: { + beautify: false, + preamble: "/* uglified */" + } +}; +var result = UglifyJS.minify(code, options); +console.log(result.code); +// /* uglified */ +// alert(10);" +``` + +To produce warnings: +```javascript +var code = "function f(){ var u; return 2 + 3; }"; +var options = { warnings: true }; +var result = UglifyJS.minify(code, options); +console.log(result.error); // runtime error, `undefined` in this case +console.log(result.warnings); // [ 'Dropping unused variable u [0:1,18]' ] +console.log(result.code); // function f(){return 5} +``` + +An error example: +```javascript +var result = UglifyJS.minify({"foo.js" : "if (0) else console.log(1);"}); +console.log(JSON.stringify(result.error)); +// {"message":"Unexpected token: keyword (else)","filename":"foo.js","line":1,"col":7,"pos":7} +``` +Note: unlike `uglify-js@2.x`, the `3.x` API does not throw errors. To +achieve a similar effect one could do the following: +```javascript +var result = UglifyJS.minify(code, options); +if (result.error) throw result.error; +``` + +## Minify options + +- `warnings` (default `false`) — pass `true` to return compressor warnings + in `result.warnings`. Use the value `"verbose"` for more detailed warnings. + +- `parse` (default `{}`) — pass an object if you wish to specify some + additional [parse options](#parse-options). + +- `compress` (default `{}`) — pass `false` to skip compressing entirely. + Pass an object to specify custom [compress options](#compress-options). + +- `mangle` (default `true`) — pass `false` to skip mangling names, or pass + an object to specify [mangle options](#mangle-options) (see below). + + - `mangle.properties` (default `false`) — a subcategory of the mangle option. + Pass an object to specify custom [mangle property options](#mangle-properties-options). + +- `output` (default `null`) — pass an object if you wish to specify + additional [output options](#output-options). The defaults are optimized + for best compression. + +- `sourceMap` (default `false`) - pass an object if you wish to specify + [source map options](#source-map-options). + +- `toplevel` (default `false`) - set to `true` if you wish to enable top level + variable and function name mangling and to drop unused variables and functions. + +- `nameCache` (default `null`) - pass an empty object `{}` or a previously + used `nameCache` object if you wish to cache mangled variable and + property names across multiple invocations of `minify()`. Note: this is + a read/write property. `minify()` will read the name cache state of this + object and update it during minification so that it may be + reused or externally persisted by the user. + +- `ie8` (default `false`) - set to `true` to support IE8. + +- `keep_fnames` (default: `false`) - pass `true` to prevent discarding or mangling + of function names. Useful for code relying on `Function.prototype.name`. + +## Minify options structure + +```javascript +{ + parse: { + // parse options + }, + compress: { + // compress options + }, + mangle: { + // mangle options + + properties: { + // mangle property options + } + }, + output: { + // output options + }, + sourceMap: { + // source map options + }, + nameCache: null, // or specify a name cache object + toplevel: false, + ie8: false, + warnings: false, +} +``` + +### Source map options + +To generate a source map: +```javascript +var result = UglifyJS.minify({"file1.js": "var a = function() {};"}, { + sourceMap: { + filename: "out.js", + url: "out.js.map" + } +}); +console.log(result.code); // minified output +console.log(result.map); // source map +``` + +Note that the source map is not saved in a file, it's just returned in +`result.map`. The value passed for `sourceMap.url` is only used to set +`//# sourceMappingURL=out.js.map` in `result.code`. The value of +`filename` is only used to set `file` attribute (see [the spec][sm-spec]) +in source map file. + +You can set option `sourceMap.url` to be `"inline"` and source map will +be appended to code. + +You can also specify sourceRoot property to be included in source map: +```javascript +var result = UglifyJS.minify({"file1.js": "var a = function() {};"}, { + sourceMap: { + root: "http://example.com/src", + url: "out.js.map" + } +}); +``` + +If you're compressing compiled JavaScript and have a source map for it, you +can use `sourceMap.content`: +```javascript +var result = UglifyJS.minify({"compiled.js": "compiled code"}, { + sourceMap: { + content: "content from compiled.js.map", + url: "minified.js.map" + } +}); +// same as before, it returns `code` and `map` +``` + +If you're using the `X-SourceMap` header instead, you can just omit `sourceMap.url`. + +## Parse options + +- `bare_returns` (default `false`) -- support top level `return` statements + +- `html5_comments` (default `true`) + +- `shebang` (default `true`) -- support `#!command` as the first line + +## Compress options + +- `arguments` (default: `true`) -- replace `arguments[index]` with function + parameter name whenever possible. + +- `booleans` (default: `true`) -- various optimizations for boolean context, + for example `!!a ? b : c → a ? b : c` + +- `collapse_vars` (default: `true`) -- Collapse single-use non-constant variables, + side effects permitting. + +- `comparisons` (default: `true`) -- apply certain optimizations to binary nodes, + e.g. `!(a <= b) → a > b`, attempts to negate binary nodes, e.g. + `a = !b && !c && !d && !e → a=!(b||c||d||e)` etc. + +- `conditionals` (default: `true`) -- apply optimizations for `if`-s and conditional + expressions + +- `dead_code` (default: `true`) -- remove unreachable code + +- `directives` (default: `true`) -- remove redundant or non-standard directives + +- `drop_console` (default: `false`) -- Pass `true` to discard calls to + `console.*` functions. If you wish to drop a specific function call + such as `console.info` and/or retain side effects from function arguments + after dropping the function call then use `pure_funcs` instead. + +- `drop_debugger` (default: `true`) -- remove `debugger;` statements + +- `evaluate` (default: `true`) -- attempt to evaluate constant expressions + +- `expression` (default: `false`) -- Pass `true` to preserve completion values + from terminal statements without `return`, e.g. in bookmarklets. + +- `global_defs` (default: `{}`) -- see [conditional compilation](#conditional-compilation) + +- `hoist_funs` (default: `false`) -- hoist function declarations + +- `hoist_props` (default: `true`) -- hoist properties from constant object and + array literals into regular variables subject to a set of constraints. For example: + `var o={p:1, q:2}; f(o.p, o.q);` is converted to `f(1, 2);`. Note: `hoist_props` + works best with `mangle` enabled, the `compress` option `passes` set to `2` or higher, + and the `compress` option `toplevel` enabled. + +- `hoist_vars` (default: `false`) -- hoist `var` declarations (this is `false` + by default because it seems to increase the size of the output in general) + +- `if_return` (default: `true`) -- optimizations for if/return and if/continue + +- `inline` (default: `true`) -- inline calls to function with simple/`return` statement: + - `false` -- same as `0` + - `0` -- disabled inlining + - `1` -- inline simple functions + - `2` -- inline functions with arguments + - `3` -- inline functions with arguments and variables + - `true` -- same as `3` + +- `join_vars` (default: `true`) -- join consecutive `var` statements + +- `keep_fargs` (default: `true`) -- Prevents the compressor from discarding unused + function arguments. You need this for code which relies on `Function.length`. + +- `keep_fnames` (default: `false`) -- Pass `true` to prevent the + compressor from discarding function names. Useful for code relying on + `Function.prototype.name`. See also: the `keep_fnames` [mangle option](#mangle). + +- `keep_infinity` (default: `false`) -- Pass `true` to prevent `Infinity` from + being compressed into `1/0`, which may cause performance issues on Chrome. + +- `loops` (default: `true`) -- optimizations for `do`, `while` and `for` loops + when we can statically determine the condition. + +- `negate_iife` (default: `true`) -- negate "Immediately-Called Function Expressions" + where the return value is discarded, to avoid the parens that the + code generator would insert. + +- `passes` (default: `1`) -- The maximum number of times to run compress. + In some cases more than one pass leads to further compressed code. Keep in + mind more passes will take more time. + +- `properties` (default: `true`) -- rewrite property access using the dot notation, for + example `foo["bar"] → foo.bar` + +- `pure_funcs` (default: `null`) -- You can pass an array of names and + UglifyJS will assume that those functions do not produce side + effects. DANGER: will not check if the name is redefined in scope. + An example case here, for instance `var q = Math.floor(a/b)`. If + variable `q` is not used elsewhere, UglifyJS will drop it, but will + still keep the `Math.floor(a/b)`, not knowing what it does. You can + pass `pure_funcs: [ 'Math.floor' ]` to let it know that this + function won't produce any side effect, in which case the whole + statement would get discarded. The current implementation adds some + overhead (compression will be slower). Make sure symbols under `pure_funcs` + are also under `mangle.reserved` to avoid mangling. + +- `pure_getters` (default: `"strict"`) -- If you pass `true` for + this, UglifyJS will assume that object property access + (e.g. `foo.bar` or `foo["bar"]`) doesn't have any side effects. + Specify `"strict"` to treat `foo.bar` as side-effect-free only when + `foo` is certain to not throw, i.e. not `null` or `undefined`. + +- `reduce_funcs` (default: `true`) -- Allows single-use functions to be + inlined as function expressions when permissible allowing further + optimization. Enabled by default. Option depends on `reduce_vars` + being enabled. Some code runs faster in the Chrome V8 engine if this + option is disabled. Does not negatively impact other major browsers. + +- `reduce_vars` (default: `true`) -- Improve optimization on variables assigned with and + used as constant values. + +- `sequences` (default: `true`) -- join consecutive simple statements using the + comma operator. May be set to a positive integer to specify the maximum number + of consecutive comma sequences that will be generated. If this option is set to + `true` then the default `sequences` limit is `200`. Set option to `false` or `0` + to disable. The smallest `sequences` length is `2`. A `sequences` value of `1` + is grandfathered to be equivalent to `true` and as such means `200`. On rare + occasions the default sequences limit leads to very slow compress times in which + case a value of `20` or less is recommended. + +- `side_effects` (default: `true`) -- Pass `false` to disable potentially dropping + functions marked as "pure". A function call is marked as "pure" if a comment + annotation `/*@__PURE__*/` or `/*#__PURE__*/` immediately precedes the call. For + example: `/*@__PURE__*/foo();` + +- `switches` (default: `true`) -- de-duplicate and remove unreachable `switch` branches + +- `toplevel` (default: `false`) -- drop unreferenced functions (`"funcs"`) and/or + variables (`"vars"`) in the top level scope (`false` by default, `true` to drop + both unreferenced functions and variables) + +- `top_retain` (default: `null`) -- prevent specific toplevel functions and + variables from `unused` removal (can be array, comma-separated, RegExp or + function. Implies `toplevel`) + +- `typeofs` (default: `true`) -- Transforms `typeof foo == "undefined"` into + `foo === void 0`. Note: recommend to set this value to `false` for IE10 and + earlier versions due to known issues. + +- `unsafe` (default: `false`) -- apply "unsafe" transformations (discussion below) + +- `unsafe_comps` (default: `false`) -- compress expressions like `a <= b` assuming + none of the operands can be (coerced to) `NaN`. + +- `unsafe_Function` (default: `false`) -- compress and mangle `Function(args, code)` + when both `args` and `code` are string literals. + +- `unsafe_math` (default: `false`) -- optimize numerical expressions like + `2 * x * 3` into `6 * x`, which may give imprecise floating point results. + +- `unsafe_proto` (default: `false`) -- optimize expressions like + `Array.prototype.slice.call(a)` into `[].slice.call(a)` + +- `unsafe_regexp` (default: `false`) -- enable substitutions of variables with + `RegExp` values the same way as if they are constants. + +- `unsafe_undefined` (default: `false`) -- substitute `void 0` if there is a + variable named `undefined` in scope (variable name will be mangled, typically + reduced to a single character) + +- `unused` (default: `true`) -- drop unreferenced functions and variables (simple + direct variable assignments do not count as references unless set to `"keep_assign"`) + +- `warnings` (default: `false`) -- display warnings when dropping unreachable + code or unused declarations etc. + +## Mangle options + +- `eval` (default `false`) -- Pass `true` to mangle names visible in scopes + where `eval` or `with` are used. + +- `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). + +- `reserved` (default `[]`) -- Pass an array of identifiers that should be + excluded from mangling. Example: `["foo", "bar"]`. + +- `toplevel` (default `false`) -- Pass `true` to mangle names declared in the + top level scope. + +Examples: + +```javascript +// test.js +var globalVar; +function funcName(firstLongName, anotherLongName) { + var myVariable = firstLongName + anotherLongName; +} +``` +```javascript +var code = fs.readFileSync("test.js", "utf8"); + +UglifyJS.minify(code).code; +// 'function funcName(a,n){}var globalVar;' + +UglifyJS.minify(code, { mangle: { reserved: ['firstLongName'] } }).code; +// 'function funcName(firstLongName,a){}var globalVar;' + +UglifyJS.minify(code, { mangle: { toplevel: true } }).code; +// 'function n(n,a){}var a;' +``` + +### Mangle properties options + +- `builtins` (default: `false`) -- Use `true` to allow the mangling of builtin + DOM properties. Not recommended to override this setting. + +- `debug` (default: `false`) -— Mangle names with the original name still present. + Pass an empty string `""` to enable, or a non-empty string to set the debug suffix. + +- `keep_quoted` (default: `false`) -— Only mangle unquoted property names. + +- `regex` (default: `null`) -— Pass a RegExp literal to only mangle property + names matching the regular expression. + +- `reserved` (default: `[]`) -- Do not mangle property names listed in the + `reserved` array. + +## Output options + +The code generator tries to output shortest code possible by default. In +case you want beautified output, pass `--beautify` (`-b`). Optionally you +can pass additional arguments that control the code output: + +- `ascii_only` (default `false`) -- escape Unicode characters in strings and + regexps (affects directives with non-ascii characters becoming invalid) + +- `beautify` (default `true`) -- whether to actually beautify the output. + Passing `-b` will set this to true, but you might need to pass `-b` even + when you want to generate minified code, in order to specify additional + arguments, so you can use `-b beautify=false` to override it. + +- `braces` (default `false`) -- always insert braces in `if`, `for`, + `do`, `while` or `with` statements, even if their body is a single + statement. + +- `comments` (default `false`) -- pass `true` or `"all"` to preserve all + comments, `"some"` to preserve some comments, a regular expression string + (e.g. `/^!/`) or a function. + +- `indent_level` (default `4`) + +- `indent_start` (default `0`) -- prefix all lines by that many spaces + +- `inline_script` (default `true`) -- escape HTML comments and the slash in + occurrences of `</script>` in strings + +- `keep_quoted_props` (default `false`) -- when turned on, prevents stripping + quotes from property names in object literals. + +- `max_line_len` (default `false`) -- maximum line length (for uglified code) + +- `preamble` (default `null`) -- when passed it must be a string and + it will be prepended to the output literally. The source map will + adjust for this text. Can be used to insert a comment containing + licensing information, for example. + +- `preserve_line` (default `false`) -- pass `true` to retain line numbering on + a best effort basis. + +- `quote_keys` (default `false`) -- pass `true` to quote all keys in literal + objects + +- `quote_style` (default `0`) -- preferred quote style for strings (affects + quoted property names and directives as well): + - `0` -- prefers double quotes, switches to single quotes when there are + more double quotes in the string itself. `0` is best for gzip size. + - `1` -- always use single quotes + - `2` -- always use double quotes + - `3` -- always use the original quotes + +- `semicolons` (default `true`) -- separate statements with semicolons. If + you pass `false` then whenever possible we will use a newline instead of a + semicolon, leading to more readable output of uglified code (size before + gzip could be smaller; size after gzip insignificantly larger). + +- `shebang` (default `true`) -- preserve shebang `#!` in preamble (bash scripts) + +- `webkit` (default `false`) -- enable workarounds for WebKit bugs. + PhantomJS users should set this option to `true`. + +- `width` (default `80`) -- only takes effect when beautification is on, this + specifies an (orientative) line width that the beautifier will try to + obey. It refers to the width of the line text (excluding indentation). + It doesn't work very well currently, but it does make the code generated + by UglifyJS more readable. + +- `wrap_iife` (default `false`) -- pass `true` to wrap immediately invoked + function expressions. See + [#640](https://github.com/mishoo/UglifyJS2/issues/640) for more details. + +# Miscellaneous + +### Keeping copyright notices or other comments + +You can pass `--comments` to retain certain comments in the output. By +default it will keep JSDoc-style comments that contain "@preserve", +"@license" or "@cc_on" (conditional compilation for IE). You can pass +`--comments all` to keep all the comments, or a valid JavaScript regexp to +keep only comments that match this regexp. For example `--comments /^!/` +will keep comments like `/*! Copyright Notice */`. + +Note, however, that there might be situations where comments are lost. For +example: +```javascript +function f() { + /** @preserve Foo Bar */ + function g() { + // this function is never called + } + return something(); +} +``` + +Even though it has "@preserve", the comment will be lost because the inner +function `g` (which is the AST node to which the comment is attached to) is +discarded by the compressor as not referenced. + +The safest comments where to place copyright information (or other info that +needs to be kept in the output) are comments attached to toplevel nodes. + +### The `unsafe` `compress` option + +It enables some transformations that *might* break code logic in certain +contrived cases, but should be fine for most code. You might want to try it +on your own code, it should reduce the minified size. Here's what happens +when this flag is on: + +- `new Array(1, 2, 3)` or `Array(1, 2, 3)` → `[ 1, 2, 3 ]` +- `new Object()` → `{}` +- `String(exp)` or `exp.toString()` → `"" + exp` +- `new Object/RegExp/Function/Error/Array (...)` → we discard the `new` + +### Conditional compilation + +You can use the `--define` (`-d`) switch in order to declare global +variables that UglifyJS will assume to be constants (unless defined in +scope). For example if you pass `--define DEBUG=false` then, coupled with +dead code removal UglifyJS will discard the following from the output: +```javascript +if (DEBUG) { + console.log("debug stuff"); +} +``` + +You can specify nested constants in the form of `--define env.DEBUG=false`. + +UglifyJS will warn about the condition being always false and about dropping +unreachable code; for now there is no option to turn off only this specific +warning, you can pass `warnings=false` to turn off *all* warnings. + +Another way of doing that is to declare your globals as constants in a +separate file and include it into the build. For example you can have a +`build/defines.js` file with the following: +```javascript +var DEBUG = false; +var PRODUCTION = true; +// etc. +``` + +and build your code like this: + + uglifyjs build/defines.js js/foo.js js/bar.js... -c + +UglifyJS will notice the constants and, since they cannot be altered, it +will evaluate references to them to the value itself and drop unreachable +code as usual. The build will contain the `const` declarations if you use +them. If you are targeting < ES6 environments which does not support `const`, +using `var` with `reduce_vars` (enabled by default) should suffice. + +### Conditional compilation API + +You can also use conditional compilation via the programmatic API. With the difference that the +property name is `global_defs` and is a compressor property: + +```javascript +var result = UglifyJS.minify(fs.readFileSync("input.js", "utf8"), { + compress: { + dead_code: true, + global_defs: { + DEBUG: false + } + } +}); +``` + +To replace an identifier with an arbitrary non-constant expression it is +necessary to prefix the `global_defs` key with `"@"` to instruct UglifyJS +to parse the value as an expression: +```javascript +UglifyJS.minify("alert('hello');", { + compress: { + global_defs: { + "@alert": "console.log" + } + } +}).code; +// returns: 'console.log("hello");' +``` + +Otherwise it would be replaced as string literal: +```javascript +UglifyJS.minify("alert('hello');", { + compress: { + global_defs: { + "alert": "console.log" + } + } +}).code; +// returns: '"console.log"("hello");' +``` + +### Using native Uglify AST with `minify()` +```javascript +// example: parse only, produce native Uglify AST + +var result = UglifyJS.minify(code, { + parse: {}, + compress: false, + mangle: false, + output: { + ast: true, + code: false // optional - faster if false + } +}); + +// result.ast contains native Uglify AST +``` +```javascript +// example: accept native Uglify AST input and then compress and mangle +// to produce both code and native AST. + +var result = UglifyJS.minify(ast, { + compress: {}, + mangle: {}, + output: { + ast: true, + code: true // optional - faster if false + } +}); + +// result.ast contains native Uglify AST +// result.code contains the minified code in string form. +``` + +### Working with Uglify AST + +Transversal and transformation of the native AST can be performed through +[`TreeWalker`](https://github.com/mishoo/UglifyJS2/blob/master/lib/ast.js) and +[`TreeTransformer`](https://github.com/mishoo/UglifyJS2/blob/master/lib/transform.js) +respectively. + +### ESTree / SpiderMonkey AST + +UglifyJS has its own abstract syntax tree format; for +[practical reasons](http://lisperator.net/blog/uglifyjs-why-not-switching-to-spidermonkey-ast/) +we can't easily change to using the SpiderMonkey AST internally. However, +UglifyJS now has a converter which can import a SpiderMonkey AST. + +For example [Acorn][acorn] is a super-fast parser that produces a +SpiderMonkey AST. It has a small CLI utility that parses one file and dumps +the AST in JSON on the standard output. To use UglifyJS to mangle and +compress that: + + acorn file.js | uglifyjs -p spidermonkey -m -c + +The `-p spidermonkey` option tells UglifyJS that all input files are not +JavaScript, but JS code described in SpiderMonkey AST in JSON. Therefore we +don't use our own parser in this case, but just transform that AST into our +internal AST. + +### Use Acorn for parsing + +More for fun, I added the `-p acorn` option which will use Acorn to do all +the parsing. If you pass this option, UglifyJS will `require("acorn")`. + +Acorn is really fast (e.g. 250ms instead of 380ms on some 650K code), but +converting the SpiderMonkey tree that Acorn produces takes another 150ms so +in total it's a bit more than just using UglifyJS's own parser. + +[acorn]: https://github.com/ternjs/acorn +[sm-spec]: https://docs.google.com/document/d/1U1RGAehQwRypUTovF1KRlpiOFze0b-_2gc6fAH0KY0k + +### Uglify Fast Minify Mode + +It's not well known, but whitespace removal and symbol mangling accounts +for 95% of the size reduction in minified code for most JavaScript - not +elaborate code transforms. One can simply disable `compress` to speed up +Uglify builds by 3 to 4 times. In this fast `mangle`-only mode Uglify has +comparable minify speeds and gzip sizes to +[`butternut`](https://www.npmjs.com/package/butternut): + +| d3.js | minify size | gzip size | minify time (seconds) | +| --- | ---: | ---: | ---: | +| original | 451,131 | 108,733 | - | +| uglify-js@3.0.24 mangle=false, compress=false | 316,600 | 85,245 | 0.70 | +| uglify-js@3.0.24 mangle=true, compress=false | 220,216 | 72,730 | 1.13 | +| butternut@0.4.6 | 217,568 | 72,738 | 1.41 | +| uglify-js@3.0.24 mangle=true, compress=true | 212,511 | 71,560 | 3.36 | +| babili@0.1.4 | 210,713 | 72,140 | 12.64 | + +To enable fast minify mode from the CLI use: +``` +uglifyjs file.js -m +``` +To enable fast minify mode with the API use: +```js +UglifyJS.minify(code, { compress: false, mangle: true }); +``` + +#### Source maps and debugging + +Various `compress` transforms that simplify, rearrange, inline and remove code +are known to have an adverse effect on debugging with source maps. This is +expected as code is optimized and mappings are often simply not possible as +some code no longer exists. For highest fidelity in source map debugging +disable the Uglify `compress` option and just use `mangle`. + +### Compiler assumptions + +To allow for better optimizations, the compiler makes various assumptions: + +- `.toString()` and `.valueOf()` don't have side effects, and for built-in + objects they have not been overridden. +- `undefined`, `NaN` and `Infinity` have not been externally redefined. +- `arguments.callee`, `arguments.caller` and `Function.prototype.caller` are not used. +- The code doesn't expect the contents of `Function.prototype.toString()` or + `Error.prototype.stack` to be anything in particular. +- Getting and setting properties on a plain object does not cause other side effects + (using `.watch()` or `Proxy`). +- Object properties can be added, removed and modified (not prevented with + `Object.defineProperty()`, `Object.defineProperties()`, `Object.freeze()`, + `Object.preventExtensions()` or `Object.seal()`). |