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+<title>UglifyJS &ndash; a JavaScript parser/compressor/beautifier</title>
+<meta http-equiv="Content-Type" content="text/html;charset=utf-8"/>
+<meta name="generator" content="Org-mode"/>
+<meta name="generated" content="2011-12-09 14:59:08 EET"/>
+<meta name="author" content="Mihai Bazon"/>
+<meta name="description" content="a JavaScript parser/compressor/beautifier in JavaScript"/>
+<meta name="keywords" content="javascript, js, parser, compiler, compressor, mangle, minify, minifier"/>
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+
+</head>
+<body>
+
+<div id="preamble">
+
+</div>
+
+<div id="content">
+<h1 class="title">UglifyJS &ndash; a JavaScript parser/compressor/beautifier</h1>
+
+
+<div id="table-of-contents">
+<h2>Table of Contents</h2>
+<div id="text-table-of-contents">
+<ul>
+<li><a href="#sec-1">1 UglifyJS &mdash; a JavaScript parser/compressor/beautifier </a>
+<ul>
+<li><a href="#sec-1-1">1.1 Unsafe transformations </a>
+<ul>
+<li><a href="#sec-1-1-1">1.1.1 Calls involving the global Array constructor </a></li>
+<li><a href="#sec-1-1-2">1.1.2 <code>obj.toString()</code> ==&gt; <code>obj+“”</code> </a></li>
+</ul>
+</li>
+<li><a href="#sec-1-2">1.2 Install (NPM) </a></li>
+<li><a href="#sec-1-3">1.3 Install latest code from GitHub </a></li>
+<li><a href="#sec-1-4">1.4 Usage </a>
+<ul>
+<li><a href="#sec-1-4-1">1.4.1 API </a></li>
+<li><a href="#sec-1-4-2">1.4.2 Beautifier shortcoming &ndash; no more comments </a></li>
+<li><a href="#sec-1-4-3">1.4.3 Use as a code pre-processor </a></li>
+</ul>
+</li>
+<li><a href="#sec-1-5">1.5 Compression &ndash; how good is it? </a></li>
+<li><a href="#sec-1-6">1.6 Bugs? </a></li>
+<li><a href="#sec-1-7">1.7 Links </a></li>
+<li><a href="#sec-1-8">1.8 License </a></li>
+</ul>
+</li>
+</ul>
+</div>
+</div>
+
+<div id="outline-container-1" class="outline-2">
+<h2 id="sec-1"><span class="section-number-2">1</span> UglifyJS &mdash; a JavaScript parser/compressor/beautifier </h2>
+<div class="outline-text-2" id="text-1">
+
+
+<p>
+This package implements a general-purpose JavaScript
+parser/compressor/beautifier toolkit. It is developed on <a href="http://nodejs.org/">NodeJS</a>, 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 <code>exports.*</code> lines from UglifyJS sources).
+</p>
+<p>
+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 <a href="../lib/parse-js.js">parse-js.js</a> and it's a
+port to JavaScript of the excellent <a href="http://marijn.haverbeke.nl/parse-js/">parse-js</a> Common Lisp library from <a href="http://marijn.haverbeke.nl/">Marijn Haverbeke</a>.
+</p>
+<p>
+( See <a href="http://github.com/mishoo/cl-uglify-js">cl-uglify-js</a> if you're looking for the Common Lisp version of
+UglifyJS. )
+</p>
+<p>
+The second part of this package, implemented in <a href="../lib/process.js">process.js</a>, inspects and
+manipulates the AST generated by the parser to provide the following:
+</p>
+<ul>
+<li>ability to re-generate JavaScript code from the AST. Optionally
+ indented&mdash;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.
+
+</li>
+<li>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 <code>eval()</code> calls or <code>with{}</code> statements. In short, if <code>eval()</code> or
+ <code>with{}</code> 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.
+
+</li>
+<li>various small optimizations that may lead to faster code but certainly
+ lead to smaller code. Where possible, we do the following:
+
+<ul>
+<li>foo["bar"] ==&gt; foo.bar
+
+</li>
+<li>remove block brackets <code>{}</code>
+
+</li>
+<li>join consecutive var declarations:
+ var a = 10; var b = 20; ==&gt; var a=10,b=20;
+
+</li>
+<li>resolve simple constant expressions: 1 +2 * 3 ==&gt; 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.
+
+</li>
+<li>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.
+
+</li>
+<li>various optimizations for IF statements:
+
+<ul>
+<li>if (foo) bar(); else baz(); ==&gt; foo?bar():baz();
+</li>
+<li>if (!foo) bar(); else baz(); ==&gt; foo?baz():bar();
+</li>
+<li>if (foo) bar(); ==&gt; foo&amp;&amp;bar();
+</li>
+<li>if (!foo) bar(); ==&gt; foo||bar();
+</li>
+<li>if (foo) return bar(); else return baz(); ==&gt; return foo?bar():baz();
+</li>
+<li>if (foo) return bar(); else something(); ==&gt; {if(foo)return bar();something()}
+
+</li>
+</ul>
+
+</li>
+<li>remove some unreachable code and warn about it (code that follows a
+ <code>return</code>, <code>throw</code>, <code>break</code> or <code>continue</code> statement, except
+ function/variable declarations).
+
+</li>
+<li>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.
+</li>
+</ul>
+
+</li>
+</ul>
+
+
+
+</div>
+
+<div id="outline-container-1-1" class="outline-3">
+<h3 id="sec-1-1"><span class="section-number-3">1.1</span> <span class="target">Unsafe transformations</span> </h3>
+<div class="outline-text-3" id="text-1-1">
+
+
+<p>
+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
+<code>--unsafe</code> flag.
+</p>
+
+</div>
+
+<div id="outline-container-1-1-1" class="outline-4">
+<h4 id="sec-1-1-1"><span class="section-number-4">1.1.1</span> Calls involving the global Array constructor </h4>
+<div class="outline-text-4" id="text-1-1-1">
+
+
+<p>
+The following transformations occur:
+</p>
+
+
+
+<pre class="src src-js"><span class="org-keyword">new</span> <span class="org-type">Array</span>(1, 2, 3, 4) =&gt; [1,2,3,4]
+Array(a, b, c) =&gt; [a,b,c]
+<span class="org-keyword">new</span> <span class="org-type">Array</span>(5) =&gt; Array(5)
+<span class="org-keyword">new</span> <span class="org-type">Array</span>(a) =&gt; Array(a)
+</pre>
+
+
+<p>
+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.
+</p>
+<p>
+UglifyJS does handle the case where Array is redefined locally, or even
+globally but with a <code>function</code> or <code>var</code> declaration. Therefore, in the
+following cases UglifyJS <b>doesn't touch</b> calls or instantiations of Array:
+</p>
+
+
+
+<pre class="src src-js"><span class="org-comment-delimiter">// </span><span class="org-comment">case 1. globally declared variable</span>
+ <span class="org-keyword">var</span> <span class="org-variable-name">Array</span>;
+ <span class="org-keyword">new</span> <span class="org-type">Array</span>(1, 2, 3);
+ Array(a, b);
+
+ <span class="org-comment-delimiter">// </span><span class="org-comment">or (can be declared later)</span>
+ <span class="org-keyword">new</span> <span class="org-type">Array</span>(1, 2, 3);
+ <span class="org-keyword">var</span> <span class="org-variable-name">Array</span>;
+
+ <span class="org-comment-delimiter">// </span><span class="org-comment">or (can be a function)</span>
+ <span class="org-keyword">new</span> <span class="org-type">Array</span>(1, 2, 3);
+ <span class="org-keyword">function</span> <span class="org-function-name">Array</span>() { ... }
+
+<span class="org-comment-delimiter">// </span><span class="org-comment">case 2. declared in a function</span>
+ (<span class="org-keyword">function</span>(){
+ a = <span class="org-keyword">new</span> <span class="org-type">Array</span>(1, 2, 3);
+ b = Array(5, 6);
+ <span class="org-keyword">var</span> <span class="org-variable-name">Array</span>;
+ })();
+
+ <span class="org-comment-delimiter">// </span><span class="org-comment">or</span>
+ (<span class="org-keyword">function</span>(<span class="org-variable-name">Array</span>){
+ <span class="org-keyword">return</span> Array(5, 6, 7);
+ })();
+
+ <span class="org-comment-delimiter">// </span><span class="org-comment">or</span>
+ (<span class="org-keyword">function</span>(){
+ <span class="org-keyword">return</span> <span class="org-keyword">new</span> <span class="org-type">Array</span>(1, 2, 3, 4);
+ <span class="org-keyword">function</span> <span class="org-function-name">Array</span>() { ... }
+ })();
+
+ <span class="org-comment-delimiter">// </span><span class="org-comment">etc.</span>
+</pre>
+
+
+</div>
+
+</div>
+
+<div id="outline-container-1-1-2" class="outline-4">
+<h4 id="sec-1-1-2"><span class="section-number-4">1.1.2</span> <code>obj.toString()</code> ==&gt; <code>obj+“”</code> </h4>
+<div class="outline-text-4" id="text-1-1-2">
+
+
+</div>
+</div>
+
+</div>
+
+<div id="outline-container-1-2" class="outline-3">
+<h3 id="sec-1-2"><span class="section-number-3">1.2</span> Install (NPM) </h3>
+<div class="outline-text-3" id="text-1-2">
+
+
+<p>
+UglifyJS is now available through NPM &mdash; <code>npm install uglify-js</code> should do
+the job.
+</p>
+</div>
+
+</div>
+
+<div id="outline-container-1-3" class="outline-3">
+<h3 id="sec-1-3"><span class="section-number-3">1.3</span> Install latest code from GitHub </h3>
+<div class="outline-text-3" id="text-1-3">
+
+
+
+
+
+<pre class="src src-sh"><span class="org-comment-delimiter">## </span><span class="org-comment">clone the repository</span>
+mkdir -p /where/you/wanna/put/it
+<span class="org-builtin">cd</span> /where/you/wanna/put/it
+git clone git://github.com/mishoo/UglifyJS.git
+
+<span class="org-comment-delimiter">## </span><span class="org-comment">make the module available to Node</span>
+mkdir -p ~/.node_libraries/
+<span class="org-builtin">cd</span> ~/.node_libraries/
+ln -s /where/you/wanna/put/it/UglifyJS/uglify-js.js
+
+<span class="org-comment-delimiter">## </span><span class="org-comment">and if you want the CLI script too:</span>
+mkdir -p ~/bin
+<span class="org-builtin">cd</span> ~/bin
+ln -s /where/you/wanna/put/it/UglifyJS/bin/uglifyjs
+ <span class="org-comment-delimiter"># </span><span class="org-comment">(then add ~/bin to your $PATH if it's not there already)</span>
+</pre>
+
+
+</div>
+
+</div>
+
+<div id="outline-container-1-4" class="outline-3">
+<h3 id="sec-1-4"><span class="section-number-3">1.4</span> Usage </h3>
+<div class="outline-text-3" id="text-1-4">
+
+
+<p>
+There is a command-line tool that exposes the functionality of this library
+for your shell-scripting needs:
+</p>
+
+
+
+<pre class="src src-sh">uglifyjs [ options... ] [ filename ]
+</pre>
+
+
+<p>
+<code>filename</code> 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.
+</p>
+<p>
+Supported options:
+</p>
+<ul>
+<li><code>-b</code> or <code>--beautify</code> &mdash; output indented code; when passed, additional
+ options control the beautifier:
+
+<ul>
+<li><code>-i N</code> or <code>--indent N</code> &mdash; indentation level (number of spaces)
+
+</li>
+<li><code>-q</code> or <code>--quote-keys</code> &mdash; quote keys in literal objects (by default,
+ only keys that cannot be identifier names will be quotes).
+
+</li>
+</ul>
+
+</li>
+<li><code>--ascii</code> &mdash; pass this argument to encode non-ASCII characters as
+ <code>\uXXXX</code> 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).
+
+</li>
+<li><code>-nm</code> or <code>--no-mangle</code> &mdash; don't mangle names.
+
+</li>
+<li><code>-nmf</code> or <code>--no-mangle-functions</code> &ndash; in case you want to mangle variable
+ names, but not touch function names.
+
+</li>
+<li><code>-ns</code> or <code>--no-squeeze</code> &mdash; don't call <code>ast_squeeze()</code> (which does various
+ optimizations that result in smaller, less readable code).
+
+</li>
+<li><code>-mt</code> or <code>--mangle-toplevel</code> &mdash; mangle names in the toplevel scope too
+ (by default we don't do this).
+
+</li>
+<li><code>--no-seqs</code> &mdash; when <code>ast_squeeze()</code> is called (thus, unless you pass
+ <code>--no-squeeze</code>) it will reduce consecutive statements in blocks into a
+ sequence. For example, "a = 10; b = 20; foo();" will be written as
+ "a=10,b=20,foo();". In various occasions, this allows us to discard the
+ block brackets (since the block becomes a single statement). This is ON
+ by default because it seems safe and saves a few hundred bytes on some
+ libs that I tested it on, but pass <code>--no-seqs</code> to disable it.
+
+</li>
+<li><code>--no-dead-code</code> &mdash; by default, UglifyJS will remove code that is
+ obviously unreachable (code that follows a <code>return</code>, <code>throw</code>, <code>break</code> or
+ <code>continue</code> statement and is not a function/variable declaration). Pass
+ this option to disable this optimization.
+
+</li>
+<li><code>-nc</code> or <code>--no-copyright</code> &mdash; by default, <code>uglifyjs</code> will keep the initial
+ comment tokens in the generated code (assumed to be copyright information
+ etc.). If you pass this it will discard it.
+
+</li>
+<li><code>-o filename</code> or <code>--output filename</code> &mdash; put the result in <code>filename</code>. If
+ this isn't given, the result goes to standard output (or see next one).
+
+</li>
+<li><code>--overwrite</code> &mdash; if the code is read from a file (not from STDIN) and you
+ pass <code>--overwrite</code> then the output will be written in the same file.
+
+</li>
+<li><code>--ast</code> &mdash; pass this if you want to get the Abstract Syntax Tree instead
+ of JavaScript as output. Useful for debugging or learning more about the
+ internals.
+
+</li>
+<li><code>-v</code> or <code>--verbose</code> &mdash; output some notes on STDERR (for now just how long
+ each operation takes).
+
+</li>
+<li><code>-d SYMBOL[=VALUE]</code> or <code>--define SYMBOL[=VALUE]</code> &mdash; will replace
+ all instances of the specified symbol where used as an identifier
+ (except where symbol has properly declared by a var declaration or
+ use as function parameter or similar) with the specified value. This
+ argument may be specified multiple times to define multiple
+ symbols - if no value is specified the symbol will be replaced with
+ the value <code>true</code>, or you can specify a numeric value (such as
+ <code>1024</code>), a quoted string value (such as ="object"= or
+ ='https://github.com'<code>), or the name of another symbol or keyword (such as =null</code> or <code>document</code>).
+ This allows you, for example, to assign meaningful names to key
+ constant values but discard the symbolic names in the uglified
+ version for brevity/efficiency, or when used wth care, allows
+ UglifyJS to operate as a form of <b>conditional compilation</b>
+ whereby defining appropriate values may, by dint of the constant
+ folding and dead code removal features above, remove entire
+ superfluous code blocks (e.g. completely remove instrumentation or
+ trace code for production use).
+ Where string values are being defined, the handling of quotes are
+ likely to be subject to the specifics of your command shell
+ environment, so you may need to experiment with quoting styles
+ depending on your platform, or you may find the option
+ <code>--define-from-module</code> more suitable for use.
+
+</li>
+<li><code>-define-from-module SOMEMODULE</code> &mdash; will load the named module (as
+ per the NodeJS <code>require()</code> function) and iterate all the exported
+ properties of the module defining them as symbol names to be defined
+ (as if by the <code>--define</code> option) per the name of each property
+ (i.e. without the module name prefix) and given the value of the
+ property. This is a much easier way to handle and document groups of
+ symbols to be defined rather than a large number of <code>--define</code>
+ options.
+
+</li>
+<li><code>--unsafe</code> &mdash; enable other additional optimizations that are known to be
+ unsafe in some contrived situations, but could still be generally useful.
+ For now only these:
+
+<ul>
+<li>foo.toString() ==&gt; foo+""
+</li>
+<li>new Array(x,&hellip;) ==&gt; [x,&hellip;]
+</li>
+<li>new Array(x) ==&gt; Array(x)
+
+</li>
+</ul>
+
+</li>
+<li><code>--max-line-len</code> (default 32K characters) &mdash; add a newline after around
+ 32K characters. I've seen both FF and Chrome croak when all the code was
+ on a single line of around 670K. Pass &ndash;max-line-len 0 to disable this
+ safety feature.
+
+</li>
+<li><code>--reserved-names</code> &mdash; some libraries rely on certain names to be used, as
+ pointed out in issue #92 and #81, so this option allow you to exclude such
+ names from the mangler. For example, to keep names <code>require</code> and <code>$super</code>
+ intact you'd specify &ndash;reserved-names "require,$super".
+
+</li>
+<li><code>--inline-script</code> &ndash; when you want to include the output literally in an
+ HTML <code>&lt;script&gt;</code> tag you can use this option to prevent <code>&lt;/script</code> from
+ showing up in the output.
+
+</li>
+<li><code>--lift-vars</code> &ndash; when you pass this, UglifyJS will apply the following
+ transformations (see the notes in API, <code>ast_lift_variables</code>):
+
+<ul>
+<li>put all <code>var</code> declarations at the start of the scope
+</li>
+<li>make sure a variable is declared only once
+</li>
+<li>discard unused function arguments
+</li>
+<li>discard unused inner (named) functions
+</li>
+<li>finally, try to merge assignments into that one <code>var</code> declaration, if
+ possible.
+</li>
+</ul>
+
+</li>
+</ul>
+
+
+
+</div>
+
+<div id="outline-container-1-4-1" class="outline-4">
+<h4 id="sec-1-4-1"><span class="section-number-4">1.4.1</span> API </h4>
+<div class="outline-text-4" id="text-1-4-1">
+
+
+<p>
+To use the library from JavaScript, you'd do the following (example for
+NodeJS):
+</p>
+
+
+
+<pre class="src src-js"><span class="org-keyword">var</span> <span class="org-variable-name">jsp</span> = require(<span class="org-string">"uglify-js"</span>).parser;
+<span class="org-keyword">var</span> <span class="org-variable-name">pro</span> = require(<span class="org-string">"uglify-js"</span>).uglify;
+
+<span class="org-keyword">var</span> <span class="org-variable-name">orig_code</span> = <span class="org-string">"... JS code here"</span>;
+<span class="org-keyword">var</span> <span class="org-variable-name">ast</span> = jsp.parse(orig_code); <span class="org-comment-delimiter">// </span><span class="org-comment">parse code and get the initial AST</span>
+ast = pro.ast_mangle(ast); <span class="org-comment-delimiter">// </span><span class="org-comment">get a new AST with mangled names</span>
+ast = pro.ast_squeeze(ast); <span class="org-comment-delimiter">// </span><span class="org-comment">get an AST with compression optimizations</span>
+<span class="org-keyword">var</span> <span class="org-variable-name">final_code</span> = pro.gen_code(ast); <span class="org-comment-delimiter">// </span><span class="org-comment">compressed code here</span>
+</pre>
+
+
+<p>
+The above performs the full compression that is possible right now. As you
+can see, there are a sequence of steps which you can apply. For example if
+you want compressed output but for some reason you don't want to mangle
+variable names, you would simply skip the line that calls
+<code>pro.ast_mangle(ast)</code>.
+</p>
+<p>
+Some of these functions take optional arguments. Here's a description:
+</p>
+<ul>
+<li><code>jsp.parse(code, strict_semicolons)</code> &ndash; parses JS code and returns an AST.
+ <code>strict_semicolons</code> is optional and defaults to <code>false</code>. If you pass
+ <code>true</code> then the parser will throw an error when it expects a semicolon and
+ it doesn't find it. For most JS code you don't want that, but it's useful
+ if you want to strictly sanitize your code.
+
+</li>
+<li><code>pro.ast_lift_variables(ast)</code> &ndash; merge and move <code>var</code> declarations to the
+ scop of the scope; discard unused function arguments or variables; discard
+ unused (named) inner functions. It also tries to merge assignments
+ following the <code>var</code> declaration into it.
+
+<p>
+ If your code is very hand-optimized concerning <code>var</code> declarations, this
+ lifting variable declarations might actually increase size. For me it
+ helps out. On jQuery it adds 865 bytes (243 after gzip). YMMV. Also
+ note that (since it's not enabled by default) this operation isn't yet
+ heavily tested (please report if you find issues!).
+</p>
+<p>
+ Note that although it might increase the image size (on jQuery it gains
+ 865 bytes, 243 after gzip) it's technically more correct: in certain
+ situations, dead code removal might drop variable declarations, which
+ would not happen if the variables are lifted in advance.
+</p>
+<p>
+ Here's an example of what it does:
+</p></li>
+</ul>
+
+
+
+
+
+<pre class="src src-js"><span class="org-keyword">function</span> <span class="org-function-name">f</span>(<span class="org-variable-name">a</span>, <span class="org-variable-name">b</span>, <span class="org-variable-name">c</span>, <span class="org-variable-name">d</span>, <span class="org-variable-name">e</span>) {
+ <span class="org-keyword">var</span> <span class="org-variable-name">q</span>;
+ <span class="org-keyword">var</span> <span class="org-variable-name">w</span>;
+ w = 10;
+ q = 20;
+ <span class="org-keyword">for</span> (<span class="org-keyword">var</span> <span class="org-variable-name">i</span> = 1; i &lt; 10; ++i) {
+ <span class="org-keyword">var</span> <span class="org-variable-name">boo</span> = foo(a);
+ }
+ <span class="org-keyword">for</span> (<span class="org-keyword">var</span> <span class="org-variable-name">i</span> = 0; i &lt; 1; ++i) {
+ <span class="org-keyword">var</span> <span class="org-variable-name">boo</span> = bar(c);
+ }
+ <span class="org-keyword">function</span> <span class="org-function-name">foo</span>(){ ... }
+ <span class="org-keyword">function</span> <span class="org-function-name">bar</span>(){ ... }
+ <span class="org-keyword">function</span> <span class="org-function-name">baz</span>(){ ... }
+}
+
+<span class="org-comment-delimiter">// </span><span class="org-comment">transforms into ==&gt;</span>
+
+<span class="org-keyword">function</span> <span class="org-function-name">f</span>(<span class="org-variable-name">a</span>, <span class="org-variable-name">b</span>, <span class="org-variable-name">c</span>) {
+ <span class="org-keyword">var</span> <span class="org-variable-name">i</span>, <span class="org-variable-name">boo</span>, <span class="org-variable-name">w</span> = 10, <span class="org-variable-name">q</span> = 20;
+ <span class="org-keyword">for</span> (i = 1; i &lt; 10; ++i) {
+ boo = foo(a);
+ }
+ <span class="org-keyword">for</span> (i = 0; i &lt; 1; ++i) {
+ boo = bar(c);
+ }
+ <span class="org-keyword">function</span> <span class="org-function-name">foo</span>() { ... }
+ <span class="org-keyword">function</span> <span class="org-function-name">bar</span>() { ... }
+}
+</pre>
+
+
+<ul>
+<li><code>pro.ast_mangle(ast, options)</code> &ndash; generates a new AST containing mangled
+ (compressed) variable and function names. It supports the following
+ options:
+
+<ul>
+<li><code>toplevel</code> &ndash; mangle toplevel names (by default we don't touch them).
+</li>
+<li><code>except</code> &ndash; an array of names to exclude from compression.
+</li>
+<li><code>defines</code> &ndash; an object with properties named after symbols to
+ replace (see the <code>--define</code> option for the script) and the values
+ representing the AST replacement value.
+
+</li>
+</ul>
+
+</li>
+<li><code>pro.ast_squeeze(ast, options)</code> &ndash; employs further optimizations designed
+ to reduce the size of the code that <code>gen_code</code> would generate from the
+ AST. Returns a new AST. <code>options</code> can be a hash; the supported options
+ are:
+
+<ul>
+<li><code>make_seqs</code> (default true) which will cause consecutive statements in a
+ block to be merged using the "sequence" (comma) operator
+
+</li>
+<li><code>dead_code</code> (default true) which will remove unreachable code.
+
+</li>
+</ul>
+
+</li>
+<li><code>pro.gen_code(ast, options)</code> &ndash; generates JS code from the AST. By
+ default it's minified, but using the <code>options</code> argument you can get nicely
+ formatted output. <code>options</code> is, well, optional :-) and if you pass it it
+ must be an object and supports the following properties (below you can see
+ the default values):
+
+<ul>
+<li><code>beautify: false</code> &ndash; pass <code>true</code> if you want indented output
+</li>
+<li><code>indent_start: 0</code> (only applies when <code>beautify</code> is <code>true</code>) &ndash; initial
+ indentation in spaces
+</li>
+<li><code>indent_level: 4</code> (only applies when <code>beautify</code> is <code>true</code>) --
+ indentation level, in spaces (pass an even number)
+</li>
+<li><code>quote_keys: false</code> &ndash; if you pass <code>true</code> it will quote all keys in
+ literal objects
+</li>
+<li><code>space_colon: false</code> (only applies when <code>beautify</code> is <code>true</code>) &ndash; wether
+ to put a space before the colon in object literals
+</li>
+<li><code>ascii_only: false</code> &ndash; pass <code>true</code> if you want to encode non-ASCII
+ characters as <code>\uXXXX</code>.
+</li>
+<li><code>inline_script: false</code> &ndash; pass <code>true</code> to escape occurrences of
+ <code>&lt;/script</code> in strings
+</li>
+</ul>
+
+</li>
+</ul>
+
+
+</div>
+
+</div>
+
+<div id="outline-container-1-4-2" class="outline-4">
+<h4 id="sec-1-4-2"><span class="section-number-4">1.4.2</span> Beautifier shortcoming &ndash; no more comments </h4>
+<div class="outline-text-4" id="text-1-4-2">
+
+
+<p>
+The beautifier can be used as a general purpose indentation tool. It's
+useful when you want to make a minified file readable. One limitation,
+though, is that it discards all comments, so you don't really want to use it
+to reformat your code, unless you don't have, or don't care about, comments.
+</p>
+<p>
+In fact it's not the beautifier who discards comments &mdash; they are dumped at
+the parsing stage, when we build the initial AST. Comments don't really
+make sense in the AST, and while we could add nodes for them, it would be
+inconvenient because we'd have to add special rules to ignore them at all
+the processing stages.
+</p>
+</div>
+
+</div>
+
+<div id="outline-container-1-4-3" class="outline-4">
+<h4 id="sec-1-4-3"><span class="section-number-4">1.4.3</span> Use as a code pre-processor </h4>
+<div class="outline-text-4" id="text-1-4-3">
+
+
+<p>
+The <code>--define</code> option can be used, particularly when combined with the
+constant folding logic, as a form of pre-processor to enable or remove
+particular constructions, such as might be used for instrumenting
+development code, or to produce variations aimed at a specific
+platform.
+</p>
+<p>
+The code below illustrates the way this can be done, and how the
+symbol replacement is performed.
+</p>
+
+
+
+<pre class="src src-js">CLAUSE1: <span class="org-keyword">if</span> (<span class="org-keyword">typeof</span> DEVMODE === <span class="org-string">'undefined'</span>) {
+ DEVMODE = <span class="org-constant">true</span>;
+}
+
+<span class="org-function-name">CLAUSE2</span>: <span class="org-keyword">function</span> init() {
+ <span class="org-keyword">if</span> (DEVMODE) {
+ console.log(<span class="org-string">"init() called"</span>);
+ }
+ ....
+ DEVMODE &amp;amp;&amp;amp; console.log(<span class="org-string">"init() complete"</span>);
+}
+
+<span class="org-function-name">CLAUSE3</span>: <span class="org-keyword">function</span> reportDeviceStatus(<span class="org-variable-name">device</span>) {
+ <span class="org-keyword">var</span> <span class="org-variable-name">DEVMODE</span> = device.mode, <span class="org-variable-name">DEVNAME</span> = device.name;
+ <span class="org-keyword">if</span> (DEVMODE === <span class="org-string">'open'</span>) {
+ ....
+ }
+}
+</pre>
+
+
+<p>
+When the above code is normally executed, the undeclared global
+variable <code>DEVMODE</code> will be assigned the value <b>true</b> (see <code>CLAUSE1</code>)
+and so the <code>init()</code> function (<code>CLAUSE2</code>) will write messages to the
+console log when executed, but in <code>CLAUSE3</code> a locally declared
+variable will mask access to the <code>DEVMODE</code> global symbol.
+</p>
+<p>
+If the above code is processed by UglifyJS with an argument of
+<code>--define DEVMODE=false</code> then UglifyJS will replace <code>DEVMODE</code> with the
+boolean constant value <b>false</b> within <code>CLAUSE1</code> and <code>CLAUSE2</code>, but it
+will leave <code>CLAUSE3</code> as it stands because there <code>DEVMODE</code> resolves to
+a validly declared variable.
+</p>
+<p>
+And more so, the constant-folding features of UglifyJS will recognise
+that the <code>if</code> condition of <code>CLAUSE1</code> is thus always false, and so will
+remove the test and body of <code>CLAUSE1</code> altogether (including the
+otherwise slightly problematical statement <code>false = true;</code> which it
+will have formed by replacing <code>DEVMODE</code> in the body). Similarly,
+within <code>CLAUSE2</code> both calls to <code>console.log()</code> will be removed
+altogether.
+</p>
+<p>
+In this way you can mimic, to a limited degree, the functionality of
+the C/C++ pre-processor to enable or completely remove blocks
+depending on how certain symbols are defined - perhaps using UglifyJS
+to generate different versions of source aimed at different
+environments
+</p>
+<p>
+It is recommmended (but not made mandatory) that symbols designed for
+this purpose are given names consisting of <code>UPPER_CASE_LETTERS</code> to
+distinguish them from other (normal) symbols and avoid the sort of
+clash that <code>CLAUSE3</code> above illustrates.
+</p>
+</div>
+</div>
+
+</div>
+
+<div id="outline-container-1-5" class="outline-3">
+<h3 id="sec-1-5"><span class="section-number-3">1.5</span> Compression &ndash; how good is it? </h3>
+<div class="outline-text-3" id="text-1-5">
+
+
+<p>
+Here are updated statistics. (I also updated my Google Closure and YUI
+installations).
+</p>
+<p>
+We're still a lot better than YUI in terms of compression, though slightly
+slower. We're still a lot faster than Closure, and compression after gzip
+is comparable.
+</p>
+<table border="2" cellspacing="0" cellpadding="6" rules="groups" frame="hsides">
+<caption></caption>
+<colgroup><col class="left" /><col class="left" /><col class="right" /><col class="left" /><col class="right" /><col class="left" /><col class="right" />
+</colgroup>
+<thead>
+<tr><th scope="col" class="left">File</th><th scope="col" class="left">UglifyJS</th><th scope="col" class="right">UglifyJS+gzip</th><th scope="col" class="left">Closure</th><th scope="col" class="right">Closure+gzip</th><th scope="col" class="left">YUI</th><th scope="col" class="right">YUI+gzip</th></tr>
+</thead>
+<tbody>
+<tr><td class="left">jquery-1.6.2.js</td><td class="left">91001 (0:01.59)</td><td class="right">31896</td><td class="left">90678 (0:07.40)</td><td class="right">31979</td><td class="left">101527 (0:01.82)</td><td class="right">34646</td></tr>
+<tr><td class="left">paper.js</td><td class="left">142023 (0:01.65)</td><td class="right">43334</td><td class="left">134301 (0:07.42)</td><td class="right">42495</td><td class="left">173383 (0:01.58)</td><td class="right">48785</td></tr>
+<tr><td class="left">prototype.js</td><td class="left">88544 (0:01.09)</td><td class="right">26680</td><td class="left">86955 (0:06.97)</td><td class="right">26326</td><td class="left">92130 (0:00.79)</td><td class="right">28624</td></tr>
+<tr><td class="left">thelib-full.js (DynarchLIB)</td><td class="left">251939 (0:02.55)</td><td class="right">72535</td><td class="left">249911 (0:09.05)</td><td class="right">72696</td><td class="left">258869 (0:01.94)</td><td class="right">76584</td></tr>
+</tbody>
+</table>
+
+
+</div>
+
+</div>
+
+<div id="outline-container-1-6" class="outline-3">
+<h3 id="sec-1-6"><span class="section-number-3">1.6</span> Bugs? </h3>
+<div class="outline-text-3" id="text-1-6">
+
+
+<p>
+Unfortunately, for the time being there is no automated test suite. But I
+ran the compressor manually on non-trivial code, and then I tested that the
+generated code works as expected. A few hundred times.
+</p>
+<p>
+DynarchLIB was started in times when there was no good JS minifier.
+Therefore I was quite religious about trying to write short code manually,
+and as such DL contains a lot of syntactic hacks<sup><a class="footref" name="fnr.1" href="#fn.1">1</a></sup> such as “foo == bar ? a
+= 10 : b = 20”, though the more readable version would clearly be to use
+“if/else”.
+</p>
+<p>
+Since the parser/compressor runs fine on DL and jQuery, I'm quite confident
+that it's solid enough for production use. If you can identify any bugs,
+I'd love to hear about them (<a href="http://groups.google.com/group/uglifyjs">use the Google Group</a> or email me directly).
+</p>
+</div>
+
+</div>
+
+<div id="outline-container-1-7" class="outline-3">
+<h3 id="sec-1-7"><span class="section-number-3">1.7</span> Links </h3>
+<div class="outline-text-3" id="text-1-7">
+
+
+<ul>
+<li>Twitter: <a href="http://twitter.com/UglifyJS">@UglifyJS</a>
+</li>
+<li>Project at GitHub: <a href="http://github.com/mishoo/UglifyJS">http://github.com/mishoo/UglifyJS</a>
+</li>
+<li>Google Group: <a href="http://groups.google.com/group/uglifyjs">http://groups.google.com/group/uglifyjs</a>
+</li>
+<li>Common Lisp JS parser: <a href="http://marijn.haverbeke.nl/parse-js/">http://marijn.haverbeke.nl/parse-js/</a>
+</li>
+<li>JS-to-Lisp compiler: <a href="http://github.com/marijnh/js">http://github.com/marijnh/js</a>
+</li>
+<li>Common Lisp JS uglifier: <a href="http://github.com/mishoo/cl-uglify-js">http://github.com/mishoo/cl-uglify-js</a>
+</li>
+</ul>
+
+
+</div>
+
+</div>
+
+<div id="outline-container-1-8" class="outline-3">
+<h3 id="sec-1-8"><span class="section-number-3">1.8</span> License </h3>
+<div class="outline-text-3" id="text-1-8">
+
+
+<p>
+UglifyJS is released under the BSD license:
+</p>
+
+
+
+<pre class="example">Copyright 2010 (c) Mihai Bazon &lt;mihai.bazon@gmail.com&gt;
+Based on parse-js (http://marijn.haverbeke.nl/parse-js/).
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions
+are met:
+
+ * Redistributions of source code must retain the above
+ copyright notice, this list of conditions and the following
+ disclaimer.
+
+ * Redistributions in binary form must reproduce the above
+ copyright notice, this list of conditions and the following
+ disclaimer in the documentation and/or other materials
+ provided with the distribution.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER “AS IS” AND ANY
+EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER BE
+LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY,
+OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR
+TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
+THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+SUCH DAMAGE.
+</pre>
+
+
+<div id="footnotes">
+<h2 class="footnotes">Footnotes: </h2>
+<div id="text-footnotes">
+<p class="footnote"><sup><a class="footnum" name="fn.1" href="#fnr.1">1</a></sup> I even reported a few bugs and suggested some fixes in the original
+ <a href="http://marijn.haverbeke.nl/parse-js/">parse-js</a> library, and Marijn pushed fixes literally in minutes.
+</p></div>
+</div>
+</div>
+
+</div>
+</div>
+</div>
+
+<div id="postamble">
+<p class="date">Date: 2011-12-09 14:59:08 EET</p>
+<p class="author">Author: Mihai Bazon</p>
+<p class="creator">Org version 7.7 with Emacs version 23</p>
+<a href="http://validator.w3.org/check?uri=referer">Validate XHTML 1.0</a>
+
+</div>
+</body>
+</html>