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YUI Compressor - The Yahoo! JavaScript and CSS Compressor

The YUI Compressor is a JavaScript compressor which, in addition to removing comments and white-spaces, obfuscates local variables using the smallest possible variable name. This obfuscation is safe, even when using constructs such as 'eval' or 'with' (although the compression is not optimal in those cases) Compared to jsmin, the average savings is around 20%.

The YUI Compressor is also able to safely compress CSS files. The decision on which compressor is being used is made on the file extension (js or css)





Node.js Package

You can require compressor in a Node.js package and compress files and strings in async. It still uses Java under the hood

npm i yuicompressor
var compressor = require('yuicompressor');

compressor.compress('/path/to/file or String of JS', {
    //Compressor Options:
    charset: 'utf8',
    type: 'js',
    nomunge: true,
    'line-break': 80
}, function(err, data, extra) {
    //err   If compressor encounters an error, it's stderr will be here
    //data  The compressed string, you write it out where you want it
    //extra The stderr (warnings are printed here in case you want to echo them


  • charset // defaults to 'utf8'
  • type // defaults to 'js'
  • line-break
  • nomunge
  • preserve-semi
  • disable-optimizations


  • Better Docs
  • Help Pages

Build Status

Build Status

Global Options

-h, --help
    Prints help on how to use the YUI Compressor

    Some source control tools don't like files containing lines longer than,
    say 8000 characters. The linebreak option is used in that case to split
    long lines after a specific column. It can also be used to make the code
    more readable, easier to debug (especially with the MS Script Debugger)
    Specify 0 to get a line break after each semi-colon in JavaScript, and
    after each rule in CSS.

--type js|css
    The type of compressor (JavaScript or CSS) is chosen based on the
    extension of the input file name (.js or .css) This option is required
    if no input file has been specified. Otherwise, this option is only
    required if the input file extension is neither 'js' nor 'css'.

--charset character-set
    If a supported character set is specified, the YUI Compressor will use it
    to read the input file. Otherwise, it will assume that the platform's
    default character set is being used. The output file is encoded using
    the same character set.

-o outfile

    Place output in file outfile. If not specified, the YUI Compressor will
    default to the standard output, which you can redirect to a file.
    Supports a filter syntax for expressing the output pattern when there are
    multiple input files.  ex:
        java -jar yuicompressor.jar -o '.css$:-min.css' *.css
    ... will minify all .css files and save them as -min.css

-v, --verbose
    Display informational messages and warnings.

JavaScript Only Options

    Minify only. Do not obfuscate local symbols.

    Preserve unnecessary semicolons (such as right before a '}') This option
    is useful when compressed code has to be run through JSLint (which is the
    case of YUI for example)

    Disable all the built-in micro optimizations.


  • If no input file is specified, it defaults to stdin.

  • Supports wildcards for specifying multiple input files.

  • The YUI Compressor requires Java version >= 1.5.

  • It is possible to prevent a local variable, nested function or function argument from being obfuscated by using "hints". A hint is a string that is located at the very beginning of a function body like so:

function fn (arg1, arg2, arg3) {
    "arg2:nomunge, localVar:nomunge, nestedFn:nomunge";

    var localVar;

    function nestedFn () {


The hint itself disappears from the compressed file.

  • C-style comments starting with /*! are preserved. This is useful with comments containing copyright/license information. As of 2.4.8, the '!' is no longer dropped by YUICompressor. For example:
 * Open source under the BSD License.
 * Copyright 2001 Robert Penner All rights reserved.

remains in the output, untouched by YUICompressor.

Modified Rhino Files

YUI Compressor uses a modified version of the Rhino library ( The changes were made to support JScript conditional comments, preserved comments, unescaped slash characters in regular expressions, and to allow for the optimization of escaped quotes in string literals.

Copyright And License

Copyright (c) 2013 Yahoo! Inc. All rights reserved. The copyrights embodied in the content of this file are licensed by Yahoo! Inc. under the BSD (revised) open source license.