Minify JavaScript files with UglifyJS

If you haven't used Grunt before, be sure to check out the Getting Started guide, as it explains how to create a Gruntfile as well as install and use Grunt plugins. Once you're familiar with that process, you may install this plugin with this command:

npm install grunt-contrib-uglify --save-dev

Once the plugin has been installed, it may be enabled inside your Gruntfile with this line of JavaScript:

grunt.loadNpmTasks('grunt-contrib-uglify');

Run this task with the grunt uglify command.

Task targets, files and options may be specified according to the grunt Configuring tasks guide.

This task primarily delegates to UglifyJS, so please consider their documentation as required reading for advanced configuration.

Type: Boolean Object
Default: {}

Turn on or off mangling with default options. If an Object is specified, it is passed directly to ast.mangle_names() and ast.compute_char_frequency() (mimicking command line behavior). View all options here.

Type: Boolean Object
Default: {}

Turn on or off source compression with default options. If an Object is specified, it is passed as options to UglifyJS.Compressor(). View all options here.

Type: Boolean Object
Default: false

Turns on beautification of the generated source code. View all options here

Type: Boolean
Default: false

Parse a single expression, rather than a program (for parsing JSON)

Type: string
Choices: 'min', 'gzip'
Default: 'min'

Report minification result or both minification and gzip results. This is useful to see exactly how well uglify-js is performing but using 'gzip' will make the task take 5-10x longer to complete. Example output.

Type: Boolean
Default: false

If true, a source map file will be generated in the same directory as the dest file. By default it will have the same basename as the dest file, but with a .map extension.

Type: String Function
Default: undefined

To customize the name or location of the generated source map, pass a string to indicate where to write the source map to. If a function is provided, the uglify destination is passed as the argument and the return value will be used as the file name.

Type: String Function
Default: undefined

The location of an input source map from an earlier compilation, e.g. from CoffeeScript. If a function is provided, the uglify source is passed as the argument and the return value will be used as the sourceMap name. This only makes sense when there's one source file.

Type: Boolean
Default: false

Pass this flag if you want to include the content of source files in the source map as sourcesContent property.

Type: String
Default: undefined

With this option you can customize root URL that browser will use when looking for sources.

If the sources are not absolute URLs after prepending of the sourceMap.root, the sources are resolved relative to the source map.

Type: String
Default: undefined

Override the calculated value for sourceMappingURL in the source map. This is useful if the source map location is not relative to the base path of the minified file, i.e. when using a CDN

Type: String
Default: undefined

Wrap all of the code in a closure, an easy way to make sure nothing is leaking. For variables that need to be public exports and global variables are made available. The value of wrap is the global variable exports will be available as.

Type: Boolean
Default: false

Enables to encode non-ASCII characters as \uXXXX.

Type: Boolean String Function
Default: undefined
Options: false 'all' 'some'

Turn on preservation of comments.

• false will strip all comments
• 'all' will preserve all comments in code blocks that have not been squashed or dropped
• 'some' will preserve all comments that include a closure compiler style directive (@preserve @license @cc_on)
• Function specify your own comment preservation function. You will be passed the current node and the current comment and are expected to return either true or false
• RegExp '/[RegExp]/' will preserve comments matching given RegExp or stringified RegExp

Type: String
Default: ''

This string will be prepended to the minified output. Template strings (e.g. <%= config.value %>) will be expanded automatically.

Type: String
Default: ''

This string will be appended to the minified output. Template strings (e.g. <%= config.value %>) will be expanded automatically.

Type: Boolean
Default: false

Set this to true if you still care about full compliance with Internet Explorer 6-8 quirks.

Type: Boolean Object
Default: false

Turn on or off property mangling with default options. If an Object is specified, it is passed directly to ast.mangle_properties() (mimicking command line behavior). View all options here.

Type: Boolean
Default: false

Use this flag in conjunction with mangle.properties to prevent built-in browser object properties from being mangled.

Type: Array
Default: []

Use this with mangle.properties to pass one or more JSON files containing a list of variables and object properties that should not be mangled. See the UglifyJS docs for more info on the file syntax.

Type: String
Default: ''

A string that is a path to a JSON cache file that uglify will create and use to coordinate symbol mangling between multiple runs of uglify. Note: this generated file uses the same JSON format as the exceptionsFiles files.

Type: Integer
Default: 0

Preserve or enforce quotation mark style.

• 0 will use single or double quotes such as to minimize the number of bytes (prefers double quotes when both will do)
• 1 will always use single quotes
• 2 will always use double quotes
• 3 will preserve original quotation marks

This configuration will compress and mangle the input files using the default options.

// Project configuration.
grunt.initConfig({
  uglify: {
    my_target: {
      files: {
        'dest/output.min.js': ['src/input1.js', 'src/input2.js']
      }
    }
  }
});

Specify mangle: false to prevent changes to your variable and function names.

// Project configuration.
grunt.initConfig({
  uglify: {
    options: {
      mangle: false
    },
    my_target: {
      files: {
        'dest/output.min.js': ['src/input.js']
      }
    }
  }
});

You can specify identifiers to leave untouched with an reserved array in the mangle options.

// Project configuration.
grunt.initConfig({
  uglify: {
    options: {
      mangle: {
        reserved: ['jQuery', 'Backbone']
      }
    },
    my_target: {
      files: {
        'dest/output.min.js': ['src/input.js']
      }
    }
  }
});

Generate a source map by setting the sourceMap option to true. The generated source map will be in the same directory as the destination file. Its name will be the basename of the destination file with a .map extension. Override these defaults with the sourceMapName attribute.

// Project configuration.
grunt.initConfig({
  uglify: {
    my_target: {
      options: {
        sourceMap: true,
        sourceMapName: 'path/to/sourcemap.map'
      },
      files: {
        'dest/output.min.js': ['src/input.js']
      }
    }
  }
});

Set the sourceMap.includeSources option to true to embed your sources directly into the map. To include a source map from a previous compilation pass it as the value of the sourceMapIn option.

// Project configuration.
grunt.initConfig({
  uglify: {
    my_target: {
      options: {
        sourceMap: {
          includeSources: true
        },
        sourceMapIn: 'example/coffeescript-sourcemap.js', // input sourcemap from a previous compilation
      },
      files: {
        'dest/output.min.js': ['src/input.js'],
      },
    },
  },
});

Refer to the UglifyJS SourceMap Documentation for more information.

Specify drop_console: true as part of the compress options to discard calls to console.* functions. This will suppress warning messages in the console.

// Project configuration.
grunt.initConfig({
  uglify: {
    options: {
      compress: {
        drop_console: true
      }
    },
    my_target: {
      files: {
        'dest/output.min.js': ['src/input.js']
      }
    }
  }
});

Specify beautify: true to beautify your code for debugging/troubleshooting purposes. Pass an object to manually configure any other output options.

See UglifyJS documentation for more information.

// Project configuration.
grunt.initConfig({
  uglify: {
    my_target: {
      options: {
        beautify: true
      },
      files: {
        'dest/output.min.js': ['src/input.js']
      }
    },
    my_advanced_target: {
      options: {
        beautify: {
          width: 80
        }
      },
      files: {
        'dest/output.min.js': ['src/input.js']
      }
    }
  }
});

In this example, running grunt uglify:my_target will prepend a banner created by interpolating the banner template string with the config object. Here, those properties are the values imported from the package.json file (which are available via the pkg config property) plus today's date.

Note: you don't have to use an external JSON file. It's also valid to create the pkg object inline in the config. That being said, if you already have a JSON file, you might as well reference it.

// Project configuration.
grunt.initConfig({
  pkg: grunt.file.readJSON('package.json'),
  uglify: {
    options: {
      banner: '/*! <%= pkg.name %> - v<%= pkg.version %> - ' +
        '<%= grunt.template.today("yyyy-mm-dd") %> */'
    },
    my_target: {
      files: {
        'dest/output.min.js': ['src/input.js']
      }
    }
  }
});

You can also enable UglifyJS conditional compilation. This is commonly used to remove debug code blocks for production builds. This is equivalent to the command line --define option.

See UglifyJS global definitions documentation for more information.

// Project configuration.
grunt.initConfig({
  uglify: {
    options: {
      compress: {
        global_defs: {
          'DEBUG': false
        },
        dead_code: true
      }
    },
    my_target: {
      files: {
        'dest/output.min.js': ['src/input.js']
      }
    }
  }
});

This configuration will compress and mangle the files dynamically.

// Project configuration.
grunt.initConfig({
  uglify: {
    my_target: {
      files: [{
        expand: true,
        cwd: 'src/js',
        src: '**/*.js',
        dest: 'dest/js'
      }]
    }
  }
});

This configuration will compress and mangle all js files separately in each folder.

Also exclude jQuery for mangling and ignore all *.min.js files.

// Project configuration.
uglify: {
  dev: {
    options: {
      mangle: {
        reserved: ['jQuery']
      }
    },
    files: [{
      expand: true,
      src: ['dist/assets/js/*.js', '!dist/assets/js/*.min.js'],
      dest: 'dist/assets',
      cwd: '.',
      rename: function (dst, src) {
        // To keep the source js files and make new files as `*.min.js`:
        // return dst + '/' + src.replace('.js', '.min.js');
        // Or to override to src:
        return src;
      }
    }]
  }
},

This configuration will turn on object property name mangling, but not mangle built-in browser object properties. Additionally, variables and object properties listed in the myExceptionsFile.json will be mangled. For more info, on the format of the exception file format please see the UglifyJS docs.

// Project configuration.
grunt.initConfig({
  uglify: {
    options: {
      mangle: {
        properties: true
      },
      reserveDOMProperties: true,
      exceptionsFiles: [ 'myExceptionsFile.json' ]
    },
    my_target: {
      files: {
        'dest/output.min.js': ['src/input.js']
      }
    }
  }
});

Turn on use of name mangling cache to coordinate mangled symbols between outputted uglify files. uglify will the generate a JSON cache file with the name provided in the options. Note: this generated file uses the same JSON format as the exceptionsFiles files.

// Project configuration.
grunt.initConfig({
  uglify: {
    options: {
      nameCache: '.tmp/grunt-uglify-cache.json',
    },
    my_target: {
      files: {
        'dest/output1.min.js': ['src/input1.js'],
        'dest/output2.min.js': ['src/input2.js']
      }
    }
  }
});

• 2022-03-27   v5.1.0   Update dependencies. uglify-js ^3.15.2. Requires node 12+.
• 2020-07-16   v5.0.0   Requires node 10+. Update dependencies.
• 2019-03-21   v4.0.1   Update uglify-js to v3.5.0. Update dependencies.
• 2018-08-26   v4.0.0   Update dependencies. Requires Node.js >= 6.
• 2018-07-29   v3.4.0   Update uglify-js to v3.4.0.
• 2017-12-24   v3.3.0   Update uglify-js to v3.3.0.
• 2017-11-26   v3.2.1   Update uglify-js to v3.2.0.
• 2017-09-11   v3.1.0   Update uglify-js to v3.1.0.
• 2017-05-20   v3.0.1   Fix toplevel option.
• 2017-05-12   v3.0.0   Update uglify-js to v3.0.4.
• 2017-04-05   v2.3.0   Make CLI output less verbose.
• 2017-03-31   v2.2.1   Fix banner option.
• 2017-03-01   v2.2.0   Update uglify-js to v2.8.3.
• 2017-02-08   v2.1.0   Show size changes in output. Switch to object.assign.
• 2016-07-19   v2.0.0   Update uglify-js to v2.7.0. screwIE8 is enabled by default.
• 2016-07-19   v1.0.2   Update grunt to ^1.0.0. Fix beautify when passed as an object. Fix docs about report values.
• 2016-03-16   v1.0.1   Downgrade maxmin for Node.js 0.10.
• 2016-03-04   v1.0.0   Use uglify-js ~2.6.2 to fix sourcemap issue. Improve docs for global-defs and --define options. Add sourceMapUrl option. Add bare_returns option. Optionally set report verbosity level using report option.
• 2016-01-29   v0.11.1   Update lodash to ^4.0.1. Update grunt-contrib-clean to ^0.7.0. Update grunt-contrib-jshint to ^0.12.0.
• 2015-11-20   v0.11.0   Update uglify-js to ~2.6.0.
• 2015-11-12   v0.10.1   Update uglify-js to ~2.5.
• 2015-10-27   v0.10.0   Update uglify-js to ^2.5.
• 2015-08-24   v0.9.2   Update uglify-js to ^2.4.24
• 2015-04-07   v0.9.1   More fixes for mangle options.
• 2015-04-07   v0.9.0   Add hook into uglify-js's mangling functionality.
• 2015-03-30   v0.8.1   Lock uglify-js to 2.4.17 due to breaking changes.
• 2015-02-19   v0.8.0   Add screwIE8 option. Fix issue with explicit compress in Node.js 0.12.0.
• 2014-12-23   v0.7.0   Add sourceMapRoot options. Update readme descriptions. Remove reference to clean-css.
• 2014-09-17   v0.6.0   Output fixes. Add ASCIIOnly option. Other fixes.
• 2014-07-25   v0.5.1   Update chalk to ^0.5.1. Output updates.
• 2014-03-01   v0.4.0   Remove grunt-lib-contrib dependency and add more colors.
• 2014-02-27   v0.3.3   Remove unnecessary calls to grunt.template.process.
• 2014-01-22   v0.3.2   Fix handling of sourceMapIncludeSources option.
• 2014-01-20   v0.3.1   Fix relative path issue in sourcemaps.
• 2014-01-16   v0.3.0   Refactor sourcemap support.
• 2013-11-09   v0.2.7   Prepend banner if sourceMap option not set, addresses #109.
• 2013-11-08   v0.2.6   Merge #45, #53, #85 (#105 by way of duping #53). Add support for banners in uglified files with sourcemaps. Update docs.
• 2013-10-28   v0.2.5   Add warning for banners when using sourcemaps.
• 2013-09-02   v0.2.4   Update sourcemap format via #83.
• 2013-06-10   v0.2.3   Add footer option.
• 2013-05-31   v0.2.2   Revert #56 due to #58 until chrome/239660 firefox/870361 drop.
• 2013-05-22   v0.2.1   Update uglify-js to ~2.3.5 #55 #40. Change sourcemappingUrl syntax #56. Disable sorting of names for consistent mangling #44. Update docs for sourceMapRoot #47 #25.
• 2013-03-14   v0.2.0   No longer report gzip results by default. Support report option.
• 2013-01-30   v0.1.2   Add better error reporting. Support for dynamic names of multiple sourcemaps.
• 2013-02-15   v0.1.1   First official release for Grunt 0.4.0.
• 2013-01-18   v0.1.1rc6   Update grunt/gruntplugin dependencies to rc6. Change in-development grunt/gruntplugin dependency versions from tilde version ranges to specific versions.
• 2013-01-09   v0.1.1rc5   Update to work with grunt v0.4.0rc5. Switch back to this.files API.
• 2012-11-28   v0.1.0   Work in progress, not officially released yet.

Task submitted by "Cowboy" Ben Alman

This file was generated on Fri Apr 15 2022 21:00:08.