UglifyJS

UglifyJS

UglifyJS is a JavaScript compressor/minifier written in JavaScript. It also contains tools that allow one to automate working with JavaScript code:

• A parser which produces an abstract syntax tree (AST) from JavaScript code.
• A code generator which outputs JavaScript code from an AST, also providing the option to get a source map.
• A compressor (optimizer) — it uses the transformer API to optimize an AST into a smaller one.
• A mangler — reduce names of local variables to (usually) single-letters.
• A scope analyzer, which is a tool that augments the AST with information about where variables are defined/referenced etc.
• A tree walker — a simple API allowing you to do something on every node in the AST.
• A tree transformer — another API intended to transform the tree.

All the above utilities and APIs are defined in ~6500 lines of code (except for the effective generation of the source-map, which is handled by the source-map module). Compared to alternatives, UglifyJS is pretty small.

These pages document the internals of UglifyJS. For a documentation of the command-line options please see the README.

Installing (for NodeJS)

You can install UglifyJS from NPM:

npm install uglify-js

but you can also use the Git repository if you feel adventurous:

git clone git://github.com/mishoo/UglifyJS2.git
cd UglifyJS2
npm link .

Building for the browser

Once you installed it for NodeJS, UglifyJS2 provides a quick way to build itself for the browser:

uglifyjs --self -c -m -o /tmp/uglifyjs.js

Now you have it in /tmp/uglifyjs.js and can include that single file in a browser. If you need source maps you'll also have to include the Mozilla source-map module. details to be clarified

Exported API

UglifyJS is written in “classic style”, so to say — it's not using the CommonJS module system (I find it more of an annoyance than of real help, especially for prototyping/development). To load it in NodeJS there's a single file that needs to be require-d: tools/node.js. If you installed it with npm install or npm link as mentioned above, then this file is loaded when you say var UglifyJS = require("uglify-js2"). This single file will load all the others in a separate execution context, so you should not worry about messing your global environment, and it returns a single object where all the global definitions in UglifyJS are exported.

Stats

Here are some stats showing where UglifyJS2 stands compared to other minifiers. Show charts.

File	Orig.	Compressor	Min.	Gzip	Time
dojo.js.uncompressed.js	598715
		UglifyJS2	114600	41344	1.696s
		UglifyJS1	117356	42001	1.633s
		Closure	114148	41492	8.104s
		Esmangle	119048	43120	5.586s
esprima.js	126268
		UglifyJS2	46672	13105	0.696s
		UglifyJS1	46384	13149	0.594s
		Closure	45669	12982	4.121s
		Esmangle	46040	13199	2.620s
jquery-1.8.2.js	266882
		UglifyJS2	92387	33146	1.604s
		UglifyJS1	93381	33288	1.539s
		Closure	93557	33781	6.085s
		Esmangle	93159	34054	4.444s
modernizr.custom.15975.js	29277
		UglifyJS2	14435	5854	0.366s
		UglifyJS1	14505	5869	0.262s
		Closure	14401	5871	2.795s
		Esmangle	14465	5909	0.592s
mootools-core-1.4.5-full-nocompat.js	113999
		UglifyJS2	83868	26551	1.079s
		UglifyJS1	84465	26624	1.095s
		Closure	83555	26834	5.242s
		Esmangle	84709	27079	2.671s
processing-1.4.1.js	421496
		UglifyJS2	208587	61218	3.461s
		UglifyJS1	208675	61162	4.003s
		Closure	205118	61056	6.907s
		Esmangle	213476	62391	32.281s
prototype.js	180829
		UglifyJS2	91656	28354	1.158s
		UglifyJS1	93311	28516	1.086s
		Closure	89953	28190	5.773s
		Esmangle	92981	29033	3.236s
raphael.js	221137
		UglifyJS2	88481	30831	1.519s
		UglifyJS1	89360	31022	1.217s
		Closure	88411	31058	6.218s
		Esmangle	89453	31942	3.911s
underscore.js	40966
		UglifyJS2	13292	4526	0.382s
		UglifyJS1	13400	4534	0.343s
		Closure	13391	4626	2.496s
		Esmangle	13525	4767	0.655s