Ruby wrapper for UglifyJS JavaScript compressor.
JavaScript Ruby
Latest commit b183403 Apr 10, 2017 @lautis Bump version to 3.2.0


Ruby wrapper for UglifyJS JavaScript compressor.

UglifyJS currently is known to work quite well with ES5. Experimental ES6/Harmony support can be enabled with :harmony => true option. See UglifyJS2#448 for more details.

Transpiling to ES5 (with e.g. babel-transpiler) is recommended. For directly minifying ES6 code, Closure Compiler is a more suitable option.

Build Status


Uglifier is available as a ruby gem.

$ gem install uglifier

Ensure that your environment has a JavaScript interpreter supported by ExecJS. Using therubyracer gem is a safe choice if a runtime isn't already present. Note that while JScript built-in Windows 7 and older works, it is extremely slow.


require 'uglifier'"source.js"))
# => js file minified

# Or alternatively

Uglifier also supports generating source maps:

uglified, source_map =

When initializing UglifyJS, you can tune the behavior of UglifyJS by passing options. For example, if you want disable variable name mangling: => false).compile(source)

# Or
Uglifier.compile(source, :mangle => false)

Available options and their defaults are

  :output => {
    :ascii_only => true,        # Escape non-ASCII characters
    :comments => :copyright,    # Preserve comments (:all, :jsdoc, :copyright, :none, Regexp (see below))
    :inline_script => false,    # Escape occurrences of </script in strings
    :quote_keys => false,       # Quote keys in object literals
    :max_line_len => 32 * 1024, # Maximum line length in minified code
    :bracketize => false,       # Bracketize if, for, do, while or with statements, even if their body is a single statement
    :semicolons => true,        # Separate statements with semicolons
    :preserve_line => false,    # Preserve line numbers in outputs
    :beautify => false,         # Beautify output
    :indent_level => 4,         # Indent level in spaces
    :indent_start => 0,         # Starting indent level
    :space_colon => false,      # Insert space before colons (only with beautifier)
    :width => 80,               # Specify line width when beautifier is used (only with beautifier)
    :preamble => nil,           # Preamble for the generated JS file. Can be used to insert any code or comment.
    :wrap_iife => false         # Wrap IIFEs in parenthesis. Note: this disables the negate_iife compression option.
  :mangle => {
    :eval => false,             # Mangle names when eval of when is used in scope
    :except => ["$super"],      # Argument names to be excluded from mangling
    :sort => false,             # Assign shorter names to most frequently used variables. Often results in bigger output after gzip.
    :toplevel => false,         # Mangle names declared in the toplevel scope
    :properties => false,       # Mangle property names
    :keep_fnames => false       # Do not modify function names
  },                            # Mangle variable and function names, set to false to skip mangling
  :mangle_properties => {
    :regex => nil,              # A regular expression to filter property names to be mangled
    :ignore_quoted => false,    # Only mangle unquoted property names
    :debug => false,            # Mangle names with the original name still present
  }                             # Mangle property names, disabled by default
  :compress => {
    :sequences => true,         # Allow statements to be joined by commas
    :properties => true,        # Rewrite property access using the dot notation
    :dead_code => true,         # Remove unreachable code
    :drop_debugger => true,     # Remove debugger; statements
    :unsafe => false,           # Apply "unsafe" transformations
    :unsafe_comps => false,     # Reverse < and <= to > and >= to allow improved compression. This might be unsafe when an at least one of two operands is an object with computed values due the use of methods like get, or valueOf. This could cause change in execution order after operands in the comparison are switching. Compression only works if both comparisons and unsafe_comps are both set to true.
    :unsafe_proto => false,     # Optimize expressions like into []
    :conditionals => true,      # Optimize for if-s and conditional expressions
    :comparisons => true,       # Apply binary node optimizations for comparisons
    :evaluate => true,          # Attempt to evaluate constant expressions
    :booleans => true,          # Various optimizations to boolean contexts
    :loops => true,             # Optimize loops when condition can be statically determined
    :unused => true,            # Drop unreferenced functions and variables
    :toplevel => false,         # Drop unreferenced top-level functions and variables
    :top_retain => [],          # prevent specific toplevel functions and variables from `unused` removal
    :hoist_funs => true,        # Hoist function declarations
    :hoist_vars => false,       # Hoist var declarations
    :if_return => true,         # Optimizations for if/return and if/continue
    :join_vars => true,         # Join consecutive var statements
    :cascade => true,           # Cascade sequences
    :collapse_vars => false,    # Collapse single-use var and const definitions when possible.
    :reduce_vars => false,      # Collapse variables assigned with and used as constant values.
    :negate_iife => true,       # Negate immediately invoked function expressions to avoid extra parens
    :pure_getters => false,     # Assume that object property access does not have any side-effects
    :pure_funcs => nil,         # List of functions without side-effects. Can safely discard function calls when the result value is not used
    :drop_console => false,     # Drop calls to console.* functions
    :angular => false,          # Process @ngInject annotations
    :keep_fargs => false,       # Preserve unused function arguments
    :keep_fnames => false       # Do not drop names in function definitions
    :passes => 1                # Number of times to run compress. Raising the number of passes will increase compress time, but can produce slightly smaller code.
  },                            # Apply transformations to code, set to false to skip
  :define => {},                # Define values for symbol replacement
  :enclose => false,            # Enclose in output function wrapper, define replacements as key-value pairs
  :keep_fnames => false,        # Generate code safe for the poor souls relying on at run-time. Sets both compress and mangle keep_fanems to true.
  :source_map => {
    :map_url => false,          # Url for source mapping to be appended in minified source
    :url => false,              # Url for original source to be appended in minified source
    :sources_content => false,  # Include original source content in map
    :filename => nil,           # The filename of the input file
    :root => nil,               # The URL of the directory which contains :filename
    :output_filename => nil,    # The filename or URL where the minified output can be found
    :input_source_map => nil    # The contents of the source map describing the input
  :harmony => false             # Enable ES6/Harmony mode (experimental). Disabling mangling and compressing is recommended with Harmony mode.

When passing a regular expression to the output => comments option, be sure to pass a valid Ruby Regexp. The beginning and ending of comments are removed and cannot be matched (/*, */, //). For example: When matching

 * comment

use {comments: /^!/}).


Tests are run using

bundle exec rake

See CONTRIBUTING for details about working on and contributing to Uglifier.


© Ville Lautanala. Released under MIT license, see LICENSE for details.