+ +

UglifyJS – a JavaScript parser/compressor/beautifier

+ + +

1 UglifyJS — a JavaScript parser/compressor/beautifier +
- 1.1 Unsafe transformations +
  - 1.1.1 Calls involving the global Array constructor
  +
- 1.2 Install (NPM)
- 1.3 Install latest code from GitHub
- 1.4 Usage +
  - 1.4.1 API
  - 1.4.2 Beautifier shortcoming – no more comments
  +
- 1.5 Compression – how good is it?
- 1.6 Bugs?
- 1.7 Links
- 1.8 License
+

+ +

1 UglifyJS — a JavaScript parser/compressor/beautifier

+ + +

+This package implements a general-purpose JavaScript +parser/compressor/beautifier toolkit. It is developed on 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 parse-js.js and it's a +port to JavaScript of the excellent parse-js Common Lisp library from Marijn Haverbeke. +

+( See cl-uglify-js if you're looking for the Common Lisp version of +UglifyJS. ) +

+The second part of this package, implemented in 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 âbeautifyâ 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). +
+

+ + + +

+ +

1.1 Unsafe transformations

+ + +

+UglifyJS tries its best to achieve great compression while leaving the +semantics of the code intact. In general, if your code logic is broken by +UglifyJS then it's a bug in UglifyJS and you should report it and I should +fix it. :-) +

+However, I opted to include the following potentially unsafe transformations +as default behavior. Discussion is welcome, if you have ideas of how to +handle this better, or any objections to these optimizations, please let me +know. +

+ +

1.1.1 Calls involving the global Array constructor

+ + +

+The following transformations occur: +

+ + + +

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)
+

+ + + +

+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: +

+ + + +

// 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.
+

+ + + +

+ +

1.2 Install (NPM)

+ + +

+UglifyJS is now available through NPM — npm install uglify-js should do +the job. +

+ +

1.3 Install latest code from GitHub

+ + + + + +

## 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)
+

+ + + +

+ +

1.4 Usage

+ + +

+There is a command-line tool that exposes the functionality of this library +for your shell-scripting needs: +

+ + + +

uglifyjs [ options... ] [ filename ]
+

+ + + +

+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). + +
+
+--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 variable names + +
+-ns or --no-squeeze — don't call ast_squeeze() (which does various +optimizations that result in smaller, less readable code). + +
+-mt or --mangle-toplevel — mangle names in the toplevel scope too +(by default we don't do this). + +
+--no-seqs — when ast_squeeze() is called (thus, unless you pass +--no-squeeze) 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 --no-seqs to disable it. + +
+--no-dead-code — by default, UglifyJS will remove code that is +obviously unreachable (code that follows a return, throw, break or +continue statement and is not a function/variable declaration). Pass +this option to disable this optimization. + +
+-nc or --no-copyright — by default, uglifyjs will keep the initial +comment tokens in the generated code (assumed to be copyright information +etc.). If you pass this it will discard it. + +
+-o filename or --output filename — put the result in filename. If +this isn't given, the result goes to standard output (or see next one). + +
+--overwrite — if the code is read from a file (not from STDIN) and you +pass --overwrite then the output will be written in the same file. + +
+--ast — 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. + +
+-v or --verbose — output some notes on STDERR (for now just how long +each operation takes). + +
+--extra — enable additional optimizations that have not yet been +extensively tested. These might, or might not, break your code. If you +find a bug using this option, please report a test case. + +
+--unsafe — enable other additional optimizations that are known to be +unsafe in some contrived situations, but could still be generally useful. +For now only this: + +
- +foo.toString() ==> foo+"" + +
+
+--max-line-len (default 32K characters) — 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 –max-line-len 0 to disable this +safety feature. + +
+--reserved-names — 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 require and $super +intact you'd specify –reserved-names "require,$super". + +
+--inline-script – when you want to include the output literally in an +HTML <script> tag you can use this option to prevent </script from +showing up in the output. +

+ + + +

+ +

1.4.1 API

+ + +

+To use the library from JavaScript, you'd do the following (example for +NodeJS): +

+ + + +

var jsp = require("uglify-js").parser;
+var pro = require("uglify-js").uglify;
+
+var orig_code = "... JS code here";
+var ast = jsp.parse(orig_code); // parse code and get the initial AST
+ast = pro.ast_mangle(ast); // get a new AST with mangled names
+ast = pro.ast_squeeze(ast); // get an AST with compression optimizations
+var final_code = pro.gen_code(ast); // compressed code here
+

+ + + +

+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 +pro.ast_mangle(ast). +

+Some of these functions take optional arguments. Here's a description: +

+jsp.parse(code, strict_semicolons) – parses JS code and returns an AST. +strict_semicolons is optional and defaults to false. If you pass +true 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. + +
+pro.ast_mangle(ast, options) – generates a new AST containing mangled +(compressed) variable and function names. It supports the following +options: + +
- +toplevel – mangle toplevel names (by default we don't touch them). +
- +except – an array of names to exclude from compression. + +
+
+pro.ast_squeeze(ast, options) – employs further optimizations designed +to reduce the size of the code that gen_code would generate from the +AST. Returns a new AST. options can be a hash; the supported options +are: + +
- +make_seqs (default true) which will cause consecutive statements in a +block to be merged using the "sequence" (comma) operator + +
- +dead_code (default true) which will remove unreachable code. + +
+
+pro.gen_code(ast, options) – generates JS code from the AST. By +default it's minified, but using the options argument you can get nicely +formatted output. options 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): + +
- +beautify: false – pass true if you want indented output +
- +indent_start: 0 (only applies when beautify is true) – initial +indentation in spaces +
- +indent_level: 4 (only applies when beautify is true) -- +indentation level, in spaces (pass an even number) +
- +quote_keys: false – if you pass true it will quote all keys in +literal objects +
- +space_colon: false (only applies when beautify is true) – wether +to put a space before the colon in object literals +
- +ascii_only: false – pass true if you want to encode non-ASCII +characters as \uXXXX. +
- +inline_script: false – pass true to escape occurrences of +</script in strings +
+

+ + +

+ +

1.4.2 Beautifier shortcoming – no more comments

+ + +

+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. +

+In fact it's not the beautifier who discards comments — 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. +

+ +

1.5 Compression – how good is it?

+ + +

+(XXX: this is somewhat outdated. On the jQuery source code we beat Closure +by 168 bytes (560 after gzip) and by many seconds.) +

+There are a few popular JS minifiers nowadays – the two most well known +being the GoogleClosure (GCL) compiler and the YUI compressor. For some +reason they are both written in Java. I didn't really hope to beat any of +them, but finally I did – UglifyJS compresses better than the YUI +compressor, and safer than GoogleClosure. +

+I tested it on two big libraries. DynarchLIB is my own, and it's big enough +to contain probably all the JavaScript tricks known to mankind. jQuery is +definitely the most popular JavaScript library (to some people, it's a +synonym to JavaScript itself). +

+I cannot swear that there are no bugs in the generated codes, but they +appear to work fine. +

+Compression results: +

+ + ++ + + + + + + + +


Library	Orig. size	UglifyJS	YUI	GCL
DynarchLIB	636896	241441	246452 (+5011)	240439 (-1002) (buggy)
jQuery	163855	72006	79702 (+7696)	71858 (-148)

+ + +

+UglifyJS is the fastest to run. On my laptop UglifyJS takes 1.35s for +DynarchLIB, while YUI takes 2.7s and GCL takes 6.5s. +

+GoogleClosure does a lot of smart ass optimizations. I had to strive really +hard to get close to it. It should be possible to even beat it, but then +again, GCL has a gazillion lines of code and runs terribly slow, so I'm not +sure it worths spending the effort to save a few bytes. Also, GCL doesn't +cope with eval() or with{} – it just dumps a warning and proceeds to +mangle names anyway; my DynarchLIB compiled with it is buggy because of +this. +

+UglifyJS consists of ~1100 lines of code for the tokenizer/parser, and ~1100 +lines for the compressor and code generator. That should make it very +maintainable and easily extensible, so I would say it has a good place in +this field and it's bound to become the de-facto standard JS minifier. And +I shall rule the world. :-) Use it, and spread the word! +

+ +

1.6 Bugs?

+ + +

+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. +

+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 hacks¹ such as âfoo == bar ? a += 10 : b = 20â, though the more readable version would clearly be to use +âif/elseâ. +

+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 (use the Google Group or email me directly). +

+ +

1.7 Links

+ + +

+Project at GitHub: http://github.com/mishoo/UglifyJS +
+Google Group: http://groups.google.com/group/uglifyjs +
+Common Lisp JS parser: http://marijn.haverbeke.nl/parse-js/ +
+JS-to-Lisp compiler: http://github.com/marijnh/js +
+Common Lisp JS uglifier: http://github.com/mishoo/cl-uglify-js +

+ + +

+ +

1.8 License

+ + +

+UglifyJS is released under the BSD license: +

+ + + +

Copyright 2010 (c) Mihai Bazon <mihai.bazon@gmail.com>
+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 âAS ISâ 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.
+

+ + + + +

Footnotes:

¹ I even reported a few bugs and suggested some fixes in the original +parse-js library, and Marijn pushed fixes literally in minutes. +

Author: Mihai Bazon +

Date: 2011-07-14 12:50:31 EEST

HTML generated by org-mode 7.01trans in emacs 23

UglifyJS – a JavaScript parser/compressor/beautifier

1 UglifyJS — a JavaScript parser/compressor/beautifier

+ + +

+( See cl-uglify-js if you're looking for the Common Lisp version of +UglifyJS. ) +

+The second part of this package, implemented in 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 âbeautifyâ 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). +
+

+ + + +

+ +

1.1 Unsafe transformations

+ + +

+ +

1.1.1 Calls involving the global Array constructor

+ + +

+The following transformations occur: +

+ + + +

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)
+

+ + + +

// 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.
+

+ + + +

+ +

1.2 Install (NPM)

+ + +

+UglifyJS is now available through NPM — npm install uglify-js should do +the job. +

+ +

1.3 Install latest code from GitHub

+ + + + + +

## 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)
+

+ + + +

+ +

1.4 Usage

+ + +

+There is a command-line tool that exposes the functionality of this library +for your shell-scripting needs: +

+ + + +

uglifyjs [ options... ] [ filename ]
+

+ + + +

+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). + +
+
+--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 variable names + +
+-ns or --no-squeeze — don't call ast_squeeze() (which does various +optimizations that result in smaller, less readable code). + +
+-mt or --mangle-toplevel — mangle names in the toplevel scope too +(by default we don't do this). + +
+--no-seqs — when ast_squeeze() is called (thus, unless you pass +--no-squeeze) 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 --no-seqs to disable it. + +
+--no-dead-code — by default, UglifyJS will remove code that is +obviously unreachable (code that follows a return, throw, break or +continue statement and is not a function/variable declaration). Pass +this option to disable this optimization. + +
+-nc or --no-copyright — by default, uglifyjs will keep the initial +comment tokens in the generated code (assumed to be copyright information +etc.). If you pass this it will discard it. + +
+-o filename or --output filename — put the result in filename. If +this isn't given, the result goes to standard output (or see next one). + +
+--overwrite — if the code is read from a file (not from STDIN) and you +pass --overwrite then the output will be written in the same file. + +
+--ast — 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. + +
+-v or --verbose — output some notes on STDERR (for now just how long +each operation takes). + +
+--extra — enable additional optimizations that have not yet been +extensively tested. These might, or might not, break your code. If you +find a bug using this option, please report a test case. + +
+--unsafe — enable other additional optimizations that are known to be +unsafe in some contrived situations, but could still be generally useful. +For now only this: + +
- +foo.toString() ==> foo+"" + +
+
+--max-line-len (default 32K characters) — 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 –max-line-len 0 to disable this +safety feature. + +
+--reserved-names — 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 require and $super +intact you'd specify –reserved-names "require,$super". + +
+--inline-script – when you want to include the output literally in an +HTML <script> tag you can use this option to prevent </script from +showing up in the output. +

+ + + +

+ +

1.4.1 API

+ + +

+To use the library from JavaScript, you'd do the following (example for +NodeJS): +

+ + + +

var jsp = require("uglify-js").parser;
+var pro = require("uglify-js").uglify;
+
+var orig_code = "... JS code here";
+var ast = jsp.parse(orig_code); // parse code and get the initial AST
+ast = pro.ast_mangle(ast); // get a new AST with mangled names
+ast = pro.ast_squeeze(ast); // get an AST with compression optimizations
+var final_code = pro.gen_code(ast); // compressed code here
+

+ + + +

+Some of these functions take optional arguments. Here's a description: +

+jsp.parse(code, strict_semicolons) – parses JS code and returns an AST. +strict_semicolons is optional and defaults to false. If you pass +true 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. + +
+pro.ast_mangle(ast, options) – generates a new AST containing mangled +(compressed) variable and function names. It supports the following +options: + +
- +toplevel – mangle toplevel names (by default we don't touch them). +
- +except – an array of names to exclude from compression. + +
+
+pro.ast_squeeze(ast, options) – employs further optimizations designed +to reduce the size of the code that gen_code would generate from the +AST. Returns a new AST. options can be a hash; the supported options +are: + +
- +make_seqs (default true) which will cause consecutive statements in a +block to be merged using the "sequence" (comma) operator + +
- +dead_code (default true) which will remove unreachable code. + +
+
+pro.gen_code(ast, options) – generates JS code from the AST. By +default it's minified, but using the options argument you can get nicely +formatted output. options 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): + +
- +beautify: false – pass true if you want indented output +
- +indent_start: 0 (only applies when beautify is true) – initial +indentation in spaces +
- +indent_level: 4 (only applies when beautify is true) -- +indentation level, in spaces (pass an even number) +
- +quote_keys: false – if you pass true it will quote all keys in +literal objects +
- +space_colon: false (only applies when beautify is true) – wether +to put a space before the colon in object literals +
- +ascii_only: false – pass true if you want to encode non-ASCII +characters as \uXXXX. +
- +inline_script: false – pass true to escape occurrences of +</script in strings +
+

+ + +

+ +

1.4.2 Beautifier shortcoming – no more comments

+ + +

+ +

1.5 Compression – how good is it?

+ + +

+(XXX: this is somewhat outdated. On the jQuery source code we beat Closure +by 168 bytes (560 after gzip) and by many seconds.) +

+I cannot swear that there are no bugs in the generated codes, but they +appear to work fine. +

+Compression results: +

+ + ++ + + + + + + + +


Library	Orig. size	UglifyJS	YUI	GCL
DynarchLIB	636896	241441	246452 (+5011)	240439 (-1002) (buggy)
jQuery	163855	72006	79702 (+7696)	71858 (-148)

+ + +

+UglifyJS is the fastest to run. On my laptop UglifyJS takes 1.35s for +DynarchLIB, while YUI takes 2.7s and GCL takes 6.5s. +

+ +

1.6 Bugs?

+ + +

+ +

1.7 Links

+ + +

+Project at GitHub: http://github.com/mishoo/UglifyJS +
+Google Group: http://groups.google.com/group/uglifyjs +
+Common Lisp JS parser: http://marijn.haverbeke.nl/parse-js/ +
+JS-to-Lisp compiler: http://github.com/marijnh/js +
+Common Lisp JS uglifier: http://github.com/mishoo/cl-uglify-js +

+ + +

+ +

1.8 License

+ + +

+UglifyJS is released under the BSD license: +

+ + + +

Copyright 2010 (c) Mihai Bazon <mihai.bazon@gmail.com>
+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 âAS ISâ 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.
+

+ + + + +

Footnotes:

¹ I even reported a few bugs and suggested some fixes in the original +parse-js library, and Marijn pushed fixes literally in minutes. +

Author: Mihai Bazon +

Date: 2011-07-14 12:50:31 EEST

HTML generated by org-mode 7.01trans in emacs 23

UglifyJS – a JavaScript parser/compressor/beautifier

Table of Contents

1 UglifyJS — a JavaScript parser/compressor/beautifier

1.1 Unsafe transformations

1.1.1 Calls involving the global Array constructor

1.2 Install (NPM)

1.3 Install latest code from GitHub

1.4 Usage

1.4.1 API

1.4.2 Beautifier shortcoming – no more comments

1.5 Compression – how good is it?

1.6 Bugs?

1.7 Links

1.8 License

Footnotes:

UglifyJS – a JavaScript parser/compressor/beautifier

Table of Contents

1 UglifyJS — a JavaScript parser/compressor/beautifier

1.1 Unsafe transformations

1.1.1 Calls involving the global Array constructor

1.2 Install (NPM)

1.3 Install latest code from GitHub

1.4 Usage

1.4.1 API

1.4.2 Beautifier shortcoming – no more comments

1.5 Compression – how good is it?

1.6 Bugs?

1.7 Links

1.8 License

Footnotes: