Ruby wrapper for UglifyJS JavaScript compressor.

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.
  :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
  },                            # 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
  }                             # 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
    :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
    :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.
    :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       # Preserve function names
  },                            # 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
  :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

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.