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#+TITLE: UglifyJS -- a JavaScript parser/compressor/beautifier #+KEYWORDS: javascript, js, parser, compiler, compressor, mangle, minify, minifier #+DESCRIPTION: a JavaScript parser/compressor/beautifier in JavaScript #+STYLE: <link rel="stylesheet" type="text/css" href="docstyle.css" /> #+AUTHOR: Mihai Bazon #+EMAIL: mihai.bazon@gmail.com * NEW: UglifyJS2 I started working on UglifyJS's successor, version 2. It's almost a full rewrite (except for the parser which is heavily modified, everything else starts from scratch). I've detailed my reasons in the README, see the project page. [[https://github.com/mishoo/UglifyJS2][https://github.com/mishoo/UglifyJS2]] Version 1 will continue to be maintained for fixing show-stopper bugs, but no new features should be expected. * UglifyJS --- a JavaScript parser/compressor/beautifier This package implements a general-purpose JavaScript parser/compressor/beautifier toolkit. It is developed on [[http://nodejs.org/][NodeJS]], but it should work on any JavaScript platform supporting the CommonJS module system (and if your platform of choice doesn't support CommonJS, you can easily implement it, or discard the =exports.*= lines from UglifyJS sources). The tokenizer/parser generates an abstract syntax tree from JS code. You can then traverse the AST to learn more about the code, or do various manipulations on it. This part is implemented in [[../lib/parse-js.js][parse-js.js]] and it's a port to JavaScript of the excellent [[http://marijn.haverbeke.nl/parse-js/][parse-js]] Common Lisp library from [[http://marijn.haverbeke.nl/][Marijn Haverbeke]]. ( See [[http://github.com/mishoo/cl-uglify-js][cl-uglify-js]] if you're looking for the Common Lisp version of UglifyJS. ) The second part of this package, implemented in [[../lib/process.js][process.js]], inspects and manipulates the AST generated by the parser to provide the following: - ability to re-generate JavaScript code from the AST. Optionally indented---you can use this if you want to “beautify” a program that has been compressed, so that you can inspect the source. But you can also run our code generator to print out an AST without any whitespace, so you achieve compression as well. - shorten variable names (usually to single characters). Our mangler will analyze the code and generate proper variable names, depending on scope and usage, and is smart enough to deal with globals defined elsewhere, or with =eval()= calls or =with{}= statements. In short, if =eval()= or =with{}= are used in some scope, then all variables in that scope and any variables in the parent scopes will remain unmangled, and any references to such variables remain unmangled as well. - various small optimizations that may lead to faster code but certainly lead to smaller code. Where possible, we do the following: - foo["bar"] ==> foo.bar - remove block brackets ={}= - join consecutive var declarations: var a = 10; var b = 20; ==> var a=10,b=20; - resolve simple constant expressions: 1 +2 * 3 ==> 7. We only do the replacement if the result occupies less bytes; for example 1/3 would translate to 0.333333333333, so in this case we don't replace it. - consecutive statements in blocks are merged into a sequence; in many cases, this leaves blocks with a single statement, so then we can remove the block brackets. - various optimizations for IF statements: - if (foo) bar(); else baz(); ==> foo?bar():baz(); - if (!foo) bar(); else baz(); ==> foo?baz():bar(); - if (foo) bar(); ==> foo&&bar(); - if (!foo) bar(); ==> foo||bar(); - if (foo) return bar(); else return baz(); ==> return foo?bar():baz(); - if (foo) return bar(); else something(); ==> {if(foo)return bar();something()} - remove some unreachable code and warn about it (code that follows a =return=, =throw=, =break= or =continue= statement, except function/variable declarations). - act a limited version of a pre-processor (c.f. the pre-processor of C/C++) to allow you to safely replace selected global symbols with specified values. When combined with the optimisations above this can make UglifyJS operate slightly more like a compilation process, in that when certain symbols are replaced by constant values, entire code blocks may be optimised away as unreachable. ** <<Unsafe transformations>> The following transformations can in theory break code, although they're probably safe in most practical cases. To enable them you need to pass the =--unsafe= flag. *** Calls involving the global Array constructor The following transformations occur: #+BEGIN_SRC js new Array(1, 2, 3, 4) => [1,2,3,4] Array(a, b, c) => [a,b,c] new Array(5) => Array(5) new Array(a) => Array(a) #+END_SRC These are all safe if the Array name isn't redefined. JavaScript does allow one to globally redefine Array (and pretty much everything, in fact) but I personally don't see why would anyone do that. UglifyJS does handle the case where Array is redefined locally, or even globally but with a =function= or =var= declaration. Therefore, in the following cases UglifyJS *doesn't touch* calls or instantiations of Array: #+BEGIN_SRC js // case 1. globally declared variable var Array; new Array(1, 2, 3); Array(a, b); // or (can be declared later) new Array(1, 2, 3); var Array; // or (can be a function) new Array(1, 2, 3); function Array() { ... } // case 2. declared in a function (function(){ a = new Array(1, 2, 3); b = Array(5, 6); var Array; })(); // or (function(Array){ return Array(5, 6, 7); })(); // or (function(){ return new Array(1, 2, 3, 4); function Array() { ... } })(); // etc. #+END_SRC *** =obj.toString()= ==> =obj+“”= ** Install (NPM) UglifyJS is now available through NPM --- =npm install uglify-js@1= should do the job. *NOTE:* The NPM package has been upgraded to UglifyJS2. If you need to install version 1.x you need to add `@1` to the command, as I did above. I strongly suggest you to try to upgrade, though this might not be simple (v2 has a completely different AST structure and API). ** Install latest code from GitHub #+BEGIN_SRC sh ## clone the repository mkdir -p /where/you/wanna/put/it cd /where/you/wanna/put/it git clone git://github.com/mishoo/UglifyJS.git ## make the module available to Node mkdir -p ~/.node_libraries/ cd ~/.node_libraries/ ln -s /where/you/wanna/put/it/UglifyJS/uglify-js.js ## and if you want the CLI script too: mkdir -p ~/bin cd ~/bin ln -s /where/you/wanna/put/it/UglifyJS/bin/uglifyjs # (then add ~/bin to your $PATH if it's not there already) #+END_SRC ** Usage There is a command-line tool that exposes the functionality of this library for your shell-scripting needs: #+BEGIN_SRC sh uglifyjs [ options... ] [ filename ] #+END_SRC =filename= should be the last argument and should name the file from which to read the JavaScript code. If you don't specify it, it will read code from STDIN. Supported options: - =-b= or =--beautify= --- output indented code; when passed, additional options control the beautifier: - =-i N= or =--indent N= --- indentation level (number of spaces) - =-q= or =--quote-keys= --- quote keys in literal objects (by default, only keys that cannot be identifier names will be quotes). - =-c= or =----consolidate-primitive-values= --- consolidates null, Boolean, and String values. Known as aliasing in the Closure Compiler. Worsens the data compression ratio of gzip. - =--ascii= --- pass this argument to encode non-ASCII characters as =\uXXXX= sequences. By default UglifyJS won't bother to do it and will output Unicode characters instead. (the output is always encoded in UTF8, but if you pass this option you'll only get ASCII). - =-nm= or =--no-mangle= --- don't mangle names. - =-nmf= or =--no-mangle-functions= -- in case you want to ma