Google Closure Compiler

Build Status

The Closure Compiler is a tool for making JavaScript download and run faster. It is a true compiler for JavaScript. Instead of compiling from a source language to machine code, it compiles from JavaScript to better JavaScript. It parses your JavaScript, analyzes it, removes dead code and rewrites and minimizes what's left. It also checks syntax, variable references, and types, and warns about common JavaScript pitfalls.

Getting Started

Options for Getting Help

  1. Post in the Closure Compiler Discuss Group
  2. Ask a question on Stack Overflow
  3. Consult the FAQ

Building it Yourself

Note: The Closure Compiler requires Java 7 or higher.

Using Ant

  1. Download the Ant build tool.

  2. At the root of the source tree, there is an Ant file named build.xml. To use it, navigate to the same directory and type the command

    ant jar

    This will produce a jar file called build/compiler.jar.

Using Eclipse

  1. Download and open the Eclipse IDE.
  2. Navigate to File > New > Project ... and create a Java Project. Give the project a name.
  3. Select Create project from existing source and choose the root of the checked-out source tree as the existing directory.
  4. Navigate to the build.xml file. You will see all the build rules in the Outline pane. Run the jar rule to build the compiler in build/compiler.jar.


On the command line, at the root of this project, type

java -jar build/compiler.jar

This starts the compiler in interactive mode. Type

var x = 17 + 25;

then hit “Enter”, then hit “Ctrl-Z” (on Windows) or “Ctrl-D” (on Mac or Linux) and “Enter” again. The Compiler will respond:

var x=42;

The Closure Compiler has many options for reading input from a file, writing output to a file, checking your code, and running optimizations. To learn more, type

java -jar compiler.jar --help

More detailed information about running the Closure Compiler is available in the documentation.

Compiling Multiple Scripts

If you have multiple scripts, you should compile them all together with one compile command.

java -jar compiler.jar --js_output_file=out.js in1.js in2.js in3.js ...

You can also use minimatch-style globs.

# Recursively include all js files in subdirs
java -jar compiler.jar --js_output_file=out.js 'src/**.js'

# Recursively include all js files in subdirs, exclusing test files.
# Use single-quotes, so that bash doesn't try to expand the '!'
java -jar compiler.jar --js_output_file=out.js 'src/**.js' '!**_test.js'

The Closure Compiler will concatenate the files in the order they're passed at the command line.

If you're using globs or many files, you may start to run into problems with managing dependencies between scripts. In this case, you should use the Closure Library. It contains functions for enforcing dependencies between scripts, and Closure Compiler will re-order the inputs automatically.

How to Contribute

Reporting a bug

  1. First make sure that it is really a bug and not simply the way that Closure Compiler works (especially true for ADVANCED_OPTIMIZATIONS).
  1. If you still think you have found a bug, make sure someone hasn't already reported it. See the list of known issues.
  2. If it hasn't been reported yet, post a new issue. Make sure to add enough detail so that the bug can be recreated. The smaller the reproduction code, the better.

Suggesting a Feature

  1. Consult the FAQ to make sure that the behaviour you would like isn't specifically excluded (such as string inlining).
  2. Make sure someone hasn't requested the same thing. See the list of known issues.
  3. Read up on what type of feature requests are accepted.
  4. Submit your reqest as an issue.

Submitting patches

  1. All contributors must sign a contributor license agreement. See the CONTRIBUTORS file for details.
  2. To make sure your changes are of the type that will be accepted, ask about your patch on the Closure Compiler Discuss Group
  3. Fork the repository.
  4. Make your changes.
  5. Submit a pull request for your changes. A project developer will review your work and then merge your request into the project.

Closure Compiler License

Copyright 2009 The Closure Compiler Authors.

Licensed under the Apache License, Version 2.0 (the “License”); you may not use this file except in compliance with the License. You may obtain a copy of the License at

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an “AS IS” BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

Dependency Licenses



Guava Libraries

JSR 305


Protocol Buffers




Node.js Closure Compiler Externs