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|
| +UglifyJS 2
|
| +==========
|
| +[](https://travis-ci.org/mishoo/UglifyJS2)
|
| +
|
| +UglifyJS is a JavaScript parser, minifier, compressor or beautifier toolkit.
|
| +
|
| +This page documents the command line utility. For
|
| +[API and internals documentation see my website](http://lisperator.net/uglifyjs/).
|
| +There's also an
|
| +[in-browser online demo](http://lisperator.net/uglifyjs/#demo) (for Firefox,
|
| +Chrome and probably Safari).
|
| +
|
| +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
|
| +
|
| +From Git:
|
| +
|
| + git clone git://github.com/mishoo/UglifyJS2.git
|
| + cd UglifyJS2
|
| + npm link .
|
| +
|
| +Usage
|
| +-----
|
| +
|
| + uglifyjs [input files] [options]
|
| +
|
| +UglifyJS2 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 you want to read from STDIN instead, pass a single dash instead of input
|
| +files.
|
| +
|
| +The available options are:
|
| +
|
| +```
|
| + --source-map Specify an output file where to generate source map.
|
| + [string]
|
| + --source-map-root The path to the original source to be included in the
|
| + source map. [string]
|
| + --source-map-url The path to the source map to be added in //#
|
| + sourceMappingURL. Defaults to the value passed with
|
| + --source-map. [string]
|
| + --source-map-include-sources
|
| + Pass this flag if you want to include the content of
|
| + source files in the source map as sourcesContent
|
| + property. [boolean]
|
| + --in-source-map Input source map, useful if you're compressing JS that was
|
| + generated from some other original code.
|
| + --screw-ie8 Pass this flag if you don't care about full compliance
|
| + with Internet Explorer 6-8 quirks (by default UglifyJS
|
| + will try to be IE-proof). [boolean]
|
| + --expr Parse a single expression, rather than a program (for
|
| + parsing JSON) [boolean]
|
| + -p, --prefix Skip prefix for original filenames that appear in source
|
| + maps. For example -p 3 will drop 3 directories from file
|
| + names and ensure they are relative paths. You can also
|
| + specify -p relative, which will make UglifyJS figure out
|
| + itself the relative paths between original sources, the
|
| + source map and the output file. [string]
|
| + -o, --output Output file (default STDOUT).
|
| + -b, --beautify Beautify output/specify output options. [string]
|
| + -m, --mangle Mangle names/pass mangler options. [string]
|
| + -r, --reserved Reserved names to exclude from mangling.
|
| + -c, --compress Enable compressor/pass compressor options. Pass options
|
| + like -c hoist_vars=false,if_return=false. Use -c with no
|
| + argument to use the default compression options. [string]
|
| + -d, --define Global definitions [string]
|
| + -e, --enclose Embed everything in a big function, with a configurable
|
| + parameter/argument list. [string]
|
| + --comments 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 (needs to start with a slash) to keep
|
| + only comments that match.
|
| + Note that currently not *all* comments can be kept when
|
| + compression is on, because of dead code removal or
|
| + cascading statements into sequences. [string]
|
| + --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.
|
| + --stats Display operations run time on STDERR. [boolean]
|
| + --acorn Use Acorn for parsing. [boolean]
|
| + --spidermonkey Assume input files are SpiderMonkey AST format (as JSON).
|
| + [boolean]
|
| + --self Build itself (UglifyJS2) as a library (implies
|
| + --wrap=UglifyJS --export-all) [boolean]
|
| + --wrap 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.
|
| + [string]
|
| + --export-all Only used when --wrap, this tells UglifyJS to add code to
|
| + automatically export all globals. [boolean]
|
| + --lint Display some scope warnings [boolean]
|
| + -v, --verbose Verbose [boolean]
|
| + -V, --version Print version number and exit. [boolean]
|
| +```
|
| +
|
| +Specify `--output` (`-o`) to declare the output file. Otherwise the output
|
| +goes to STDOUT.
|
| +
|
| +## Source map options
|
| +
|
| +UglifyJS2 can generate a source map file, which is highly useful for
|
| +debugging your compressed JavaScript. To get a source map, pass
|
| +`--source-map output.js.map` (full path to the file where you want the
|
| +source map dumped).
|
| +
|
| +Additionally you might need `--source-map-root` to pass the URL where the
|
| +original files can be found. In case you are passing full paths to input
|
| +files to UglifyJS, you can use `--prefix` (`-p`) to specify the number of
|
| +directories to drop from the path prefix when declaring files in the source
|
| +map.
|
| +
|
| +For example:
|
| +
|
| + uglifyjs /home/doe/work/foo/src/js/file1.js \
|
| + /home/doe/work/foo/src/js/file2.js \
|
| + -o foo.min.js \
|
| + --source-map foo.min.js.map \
|
| + --source-map-root http://foo.com/src \
|
| + -p 5 -c -m
|
| +
|
| +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 you need to pass `--in-source-map
|
| +/path/to/input/source.map`. Normally the input source map should also point
|
| +to the file containing the generated JS, so if that's correct you can omit
|
| +input files from the command line.
|
| +
|
| +## Mangler options
|
| +
|
| +To enable the mangler you need to pass `--mangle` (`-m`). The following
|
| +(comma-separated) options are supported:
|
| +
|
| +- `sort` — to assign shorter names to most frequently used variables. This
|
| + saves a few hundred bytes on jQuery before gzip, but the output is
|
| + _bigger_ after gzip (and seems to happen for other libraries I tried it
|
| + on) therefore it's not enabled by default.
|
| +
|
| +- `toplevel` — mangle names declared in the toplevel scope (disabled by
|
| + default).
|
| +
|
| +- `eval` — mangle names visible in scopes where `eval` or `with` are used
|
| + (disabled by default).
|
| +
|
| +When mangling is enabled but you want to prevent certain names from being
|
| +mangled, you can declare those names with `--reserved` (`-r`) — pass a
|
| +comma-separated list of names. For example:
|
| +
|
| + uglifyjs ... -m -r '$,require,exports'
|
| +
|
| +to prevent the `require`, `exports` and `$` names from being changed.
|
| +
|
| +## Compressor options
|
| +
|
| +You need to pass `--compress` (`-c`) to enable the compressor. Optionally
|
| +you can pass a comma-separated list of 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`).
|
| +
|
| +- `sequences` -- join consecutive simple statements using the comma operator
|
| +
|
| +- `properties` -- rewrite property access using the dot notation, for
|
| + example `foo["bar"] → foo.bar`
|
| +
|
| +- `dead_code` -- remove unreachable code
|
| +
|
| +- `drop_debugger` -- remove `debugger;` statements
|
| +
|
| +- `unsafe` (default: false) -- apply "unsafe" transformations (discussion below)
|
| +
|
| +- `conditionals` -- apply optimizations for `if`-s and conditional
|
| + expressions
|
| +
|
| +- `comparisons` -- apply certain optimizations to binary nodes, for example:
|
| + `!(a <= b) → a > b` (only when `unsafe`), attempts to negate binary nodes,
|
| + e.g. `a = !b && !c && !d && !e → a=!(b||c||d||e)` etc.
|
| +
|
| +- `evaluate` -- attempt to evaluate constant expressions
|
| +
|
| +- `booleans` -- various optimizations for boolean context, for example `!!a
|
| + ? b : c → a ? b : c`
|
| +
|
| +- `loops` -- optimizations for `do`, `while` and `for` loops when we can
|
| + statically determine the condition
|
| +
|
| +- `unused` -- drop unreferenced functions and variables
|
| +
|
| +- `hoist_funs` -- hoist function declarations
|
| +
|
| +- `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` -- optimizations for if/return and if/continue
|
| +
|
| +- `join_vars` -- join consecutive `var` statements
|
| +
|
| +- `cascade` -- small optimization for sequences, transform `x, x` into `x`
|
| + and `x = something(), x` into `x = something()`
|
| +
|
| +- `warnings` -- display warnings when dropping unreachable code or unused
|
| + declarations etc.
|
| +
|
| +- `negate_iife` -- negate "Immediately-Called Function Expressions"
|
| + where the return value is discarded, to avoid the parens that the
|
| + code generator would insert.
|
| +
|
| +- `pure_getters` -- the default is `false`. 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.
|
| +
|
| +- `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).
|
| +
|
| +- `drop_console` -- default `false`. Pass `true` to discard calls to
|
| + `console.*` functions.
|
| +
|
| +- `keep_fargs` -- default `false`. Pass `true` to prevent the
|
| + compressor from discarding unused function arguments. You need this
|
| + for code which relies on `Function.length`.
|
| +
|
| +### The `unsafe` 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`
|
| +- `typeof foo == "undefined"` → `foo === void 0`
|
| +- `void 0` → `undefined` (if there is a variable named "undefined" in
|
| + scope; we do it because the variable name will be mangled, typically
|
| + reduced to a single character).
|
| +
|
| +### 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");
|
| +}
|
| +```
|
| +
|
| +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
|
| +const DEBUG = false;
|
| +const 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 possible downside of this approach is that the build
|
| +will contain the `const` declarations.
|
| +
|
| +<a name="codegen-options"></a>
|
| +## Beautifier 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:
|
| +
|
| +- `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.
|
| +- `indent-level` (default 4)
|
| +- `indent-start` (default 0) -- prefix all lines by that many spaces
|
| +- `quote-keys` (default `false`) -- pass `true` to quote all keys in literal
|
| + objects
|
| +- `space-colon` (default `true`) -- insert a space after the colon signs
|
| +- `ascii-only` (default `false`) -- escape Unicode characters in strings and
|
| + regexps
|
| +- `inline-script` (default `false`) -- escape the slash in occurrences of
|
| + `</script` in strings
|
| +- `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.
|
| +- `max-line-len` (default 32000) -- maximum line length (for uglified code)
|
| +- `bracketize` (default `false`) -- always insert brackets in `if`, `for`,
|
| + `do`, `while` or `with` statements, even if their body is a single
|
| + statement.
|
| +- `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).
|
| +- `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.
|
| +
|
| +### 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
|
| +'/foo|bar/'` will keep only comments that contain "foo" or "bar".
|
| +
|
| +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.
|
| +
|
| +## Support for the SpiderMonkey AST
|
| +
|
| +UglifyJS2 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 --spidermonkey -m -c
|
| +
|
| +The `--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 `--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.
|
| +
|
| +### Using UglifyJS to transform SpiderMonkey AST
|
| +
|
| +Now you can use UglifyJS as any other intermediate tool for transforming
|
| +JavaScript ASTs in SpiderMonkey format.
|
| +
|
| +Example:
|
| +
|
| +```javascript
|
| +function uglify(ast, options, mangle) {
|
| + // Conversion from SpiderMonkey AST to internal format
|
| + var uAST = UglifyJS.AST_Node.from_mozilla_ast(ast);
|
| +
|
| + // Compression
|
| + uAST.figure_out_scope();
|
| + uAST = uAST.transform(UglifyJS.Compressor(options));
|
| +
|
| + // Mangling (optional)
|
| + if (mangle) {
|
| + uAST.figure_out_scope();
|
| + uAST.compute_char_frequency();
|
| + uAST.mangle_names();
|
| + }
|
| +
|
| + // Back-conversion to SpiderMonkey AST
|
| + return uAST.to_mozilla_ast();
|
| +}
|
| +```
|
| +
|
| +Check out
|
| +[original blog post](http://rreverser.com/using-mozilla-ast-with-uglifyjs/)
|
| +for details.
|
| +
|
| +API Reference
|
| +-------------
|
| +
|
| +Assuming installation via NPM, you can load UglifyJS in your application
|
| +like this:
|
| +```javascript
|
| +var UglifyJS = require("uglify-js");
|
| +```
|
| +
|
| +It exports a lot of names, but I'll discuss here the basics that are needed
|
| +for parsing, mangling and compressing a piece of code. The sequence is (1)
|
| +parse, (2) compress, (3) mangle, (4) generate output code.
|
| +
|
| +### The simple way
|
| +
|
| +There's a single toplevel function which combines all the steps. If you
|
| +don't need additional customization, you might want to go with `minify`.
|
| +Example:
|
| +```javascript
|
| +var result = UglifyJS.minify("/path/to/file.js");
|
| +console.log(result.code); // minified output
|
| +// if you need to pass code instead of file name
|
| +var result = UglifyJS.minify("var b = function () {};", {fromString: true});
|
| +```
|
| +
|
| +You can also compress multiple files:
|
| +```javascript
|
| +var result = UglifyJS.minify([ "file1.js", "file2.js", "file3.js" ]);
|
| +console.log(result.code);
|
| +```
|
| +
|
| +To generate a source map:
|
| +```javascript
|
| +var result = UglifyJS.minify([ "file1.js", "file2.js", "file3.js" ], {
|
| + outSourceMap: "out.js.map"
|
| +});
|
| +console.log(result.code); // minified output
|
| +console.log(result.map);
|
| +```
|
| +
|
| +Note that the source map is not saved in a file, it's just returned in
|
| +`result.map`. The value passed for `outSourceMap` is only used to set the
|
| +`file` attribute in the source map (see [the spec][sm-spec]).
|
| +
|
| +You can also specify sourceRoot property to be included in source map:
|
| +```javascript
|
| +var result = UglifyJS.minify([ "file1.js", "file2.js", "file3.js" ], {
|
| + outSourceMap: "out.js.map",
|
| + sourceRoot: "http://example.com/src"
|
| +});
|
| +```
|
| +
|
| +If you're compressing compiled JavaScript and have a source map for it, you
|
| +can use the `inSourceMap` argument:
|
| +```javascript
|
| +var result = UglifyJS.minify("compiled.js", {
|
| + inSourceMap: "compiled.js.map",
|
| + outSourceMap: "minified.js.map"
|
| +});
|
| +// same as before, it returns `code` and `map`
|
| +```
|
| +
|
| +The `inSourceMap` is only used if you also request `outSourceMap` (it makes
|
| +no sense otherwise).
|
| +
|
| +Other options:
|
| +
|
| +- `warnings` (default `false`) — pass `true` to display compressor warnings.
|
| +
|
| +- `fromString` (default `false`) — if you pass `true` then you can pass
|
| + JavaScript source code, rather than file names.
|
| +
|
| +- `mangle` — pass `false` to skip mangling names.
|
| +
|
| +- `output` (default `null`) — pass an object if you wish to specify
|
| + additional [output options][codegen]. The defaults are optimized
|
| + for best compression.
|
| +
|
| +- `compress` (default `{}`) — pass `false` to skip compressing entirely.
|
| + Pass an object to specify custom [compressor options][compressor].
|
| +
|
| +We could add more options to `UglifyJS.minify` — if you need additional
|
| +functionality please suggest!
|
| +
|
| +### The hard way
|
| +
|
| +Following there's more detailed API info, in case the `minify` function is
|
| +too simple for your needs.
|
| +
|
| +#### The parser
|
| +```javascript
|
| +var toplevel_ast = UglifyJS.parse(code, options);
|
| +```
|
| +
|
| +`options` is optional and if present it must be an object. The following
|
| +properties are available:
|
| +
|
| +- `strict` — disable automatic semicolon insertion and support for trailing
|
| + comma in arrays and objects
|
| +- `filename` — the name of the file where this code is coming from
|
| +- `toplevel` — a `toplevel` node (as returned by a previous invocation of
|
| + `parse`)
|
| +
|
| +The last two options are useful when you'd like to minify multiple files and
|
| +get a single file as the output and a proper source map. Our CLI tool does
|
| +something like this:
|
| +```javascript
|
| +var toplevel = null;
|
| +files.forEach(function(file){
|
| + var code = fs.readFileSync(file, "utf8");
|
| + toplevel = UglifyJS.parse(code, {
|
| + filename: file,
|
| + toplevel: toplevel
|
| + });
|
| +});
|
| +```
|
| +
|
| +After this, we have in `toplevel` a big AST containing all our files, with
|
| +each token having proper information about where it came from.
|
| +
|
| +#### Scope information
|
| +
|
| +UglifyJS contains a scope analyzer that you need to call manually before
|
| +compressing or mangling. Basically it augments various nodes in the AST
|
| +with information about where is a name defined, how many times is a name
|
| +referenced, if it is a global or not, if a function is using `eval` or the
|
| +`with` statement etc. I will discuss this some place else, for now what's
|
| +important to know is that you need to call the following before doing
|
| +anything with the tree:
|
| +```javascript
|
| +toplevel.figure_out_scope()
|
| +```
|
| +
|
| +#### Compression
|
| +
|
| +Like this:
|
| +```javascript
|
| +var compressor = UglifyJS.Compressor(options);
|
| +var compressed_ast = toplevel.transform(compressor);
|
| +```
|
| +
|
| +The `options` can be missing. Available options are discussed above in
|
| +“Compressor options”. Defaults should lead to best compression in most
|
| +scripts.
|
| +
|
| +The compressor is destructive, so don't rely that `toplevel` remains the
|
| +original tree.
|
| +
|
| +#### Mangling
|
| +
|
| +After compression it is a good idea to call again `figure_out_scope` (since
|
| +the compressor might drop unused variables / unreachable code and this might
|
| +change the number of identifiers or their position). Optionally, you can
|
| +call a trick that helps after Gzip (counting character frequency in
|
| +non-mangleable words). Example:
|
| +```javascript
|
| +compressed_ast.figure_out_scope();
|
| +compressed_ast.compute_char_frequency();
|
| +compressed_ast.mangle_names();
|
| +```
|
| +
|
| +#### Generating output
|
| +
|
| +AST nodes have a `print` method that takes an output stream. Essentially,
|
| +to generate code you do this:
|
| +```javascript
|
| +var stream = UglifyJS.OutputStream(options);
|
| +compressed_ast.print(stream);
|
| +var code = stream.toString(); // this is your minified code
|
| +```
|
| +
|
| +or, for a shortcut you can do:
|
| +```javascript
|
| +var code = compressed_ast.print_to_string(options);
|
| +```
|
| +
|
| +As usual, `options` is optional. The output stream accepts a lot of otions,
|
| +most of them documented above in section “Beautifier options”. The two
|
| +which we care about here are `source_map` and `comments`.
|
| +
|
| +#### Keeping comments in the output
|
| +
|
| +In order to keep certain comments in the output you need to pass the
|
| +`comments` option. Pass a RegExp or a function. If you pass a RegExp, only
|
| +those comments whose body matches the regexp will be kept. Note that body
|
| +means without the initial `//` or `/*`. If you pass a function, it will be
|
| +called for every comment in the tree and will receive two arguments: the
|
| +node that the comment is attached to, and the comment token itself.
|
| +
|
| +The comment token has these properties:
|
| +
|
| +- `type`: "comment1" for single-line comments or "comment2" for multi-line
|
| + comments
|
| +- `value`: the comment body
|
| +- `pos` and `endpos`: the start/end positions (zero-based indexes) in the
|
| + original code where this comment appears
|
| +- `line` and `col`: the line and column where this comment appears in the
|
| + original code
|
| +- `file` — the file name of the original file
|
| +- `nlb` — true if there was a newline before this comment in the original
|
| + code, or if this comment contains a newline.
|
| +
|
| +Your function should return `true` to keep the comment, or a falsy value
|
| +otherwise.
|
| +
|
| +#### Generating a source mapping
|
| +
|
| +You need to pass the `source_map` argument when calling `print`. It needs
|
| +to be a `SourceMap` object (which is a thin wrapper on top of the
|
| +[source-map][source-map] library).
|
| +
|
| +Example:
|
| +```javascript
|
| +var source_map = UglifyJS.SourceMap(source_map_options);
|
| +var stream = UglifyJS.OutputStream({
|
| + ...
|
| + source_map: source_map
|
| +});
|
| +compressed_ast.print(stream);
|
| +
|
| +var code = stream.toString();
|
| +var map = source_map.toString(); // json output for your source map
|
| +```
|
| +
|
| +The `source_map_options` (optional) can contain the following properties:
|
| +
|
| +- `file`: the name of the JavaScript output file that this mapping refers to
|
| +- `root`: the `sourceRoot` property (see the [spec][sm-spec])
|
| +- `orig`: the "original source map", handy when you compress generated JS
|
| + and want to map the minified output back to the original code where it
|
| + came from. It can be simply a string in JSON, or a JSON object containing
|
| + the original source map.
|
| +
|
| + [acorn]: https://github.com/marijnh/acorn
|
| + [source-map]: https://github.com/mozilla/source-map
|
| + [sm-spec]: https://docs.google.com/document/d/1U1RGAehQwRypUTovF1KRlpiOFze0b-_2gc6fAH0KY0k/edit
|
| + [codegen]: http://lisperator.net/uglifyjs/codegen
|
| + [compressor]: http://lisperator.net/uglifyjs/compress
|
|
|