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.

• Download the latest version (Release details here)
• Download a specific version. Also available via:
  • Maven
  • NPM
• Use the JavaScript version, with no Java dependency
• See the Google Developers Site for documentation including instructions for running the compiler from the command line.

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

Note: The Closure Compiler requires Java 7 or higher.

1. Download Maven.

2. Add sonatype snapshots repository to ~/.m2/settings.xml:

   <profile>
     <id>allow-snapshots</id>
        <activation><activeByDefault>true</activeByDefault></activation>
     <repositories>
       <repository>
         <id>snapshots-repo</id>
         <url>https://oss.sonatype.org/content/repositories/snapshots</url>
         <releases><enabled>false</enabled></releases>
         <snapshots><enabled>true</enabled></snapshots>
       </repository>
     </repositories>
   </profile>
   

3. Run mvn -DskipTests (omit the -DskipTests if you want to run all the unit tests too).

   This will produce a jar file called target/closure-compiler-1.0-SNAPSHOT.jar.

   Running mvn -DskipTests -pl externs/pom.xml,pom-main.xml,pom-main-shaded.xml will skip building the GWT version of the compiler. This can speed up the build process significantly.

1. Download and open the Eclipse IDE.
2. Run mvn eclipse:eclipse -DdownloadSources=true to download JARs and build Eclipse project configuration.
3. Navigate to File > Import > Maven > Existing Maven Projects and browse to closure-compiler.
4. Import both closure-compiler and the nested externs project.
5. Disregard the warnings about maven-antrun-plugin and build errors.
6. In Package Explorer, remove from the build path:
   • src/com/google/javascript/jscomp/debugger/DebuggerGwtMain.java
   • src/com/google/javascript/jscomp/gwt/
7. See Using Maven above to build the JAR.

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

java -jar target/closure-compiler-1.0-SNAPSHOT.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.

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, excluding 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.

1. First make sure that it is really a bug and not simply the way that Closure Compiler works (especially true for ADVANCED_OPTIMIZATIONS).

• Check the official documentation
• Consult the FAQ
• Search on Stack Overflow and in the Closure Compiler Discuss Group

2. If you still think you have found a bug, make sure someone hasn't already reported it. See the list of known issues.
3. 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.

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 request as an issue.

1. All contributors must sign a contributor license agreement (CLA). A CLA basically says that you own the rights to any code you contribute, and that you give us permission to use that code in Closure Compiler. You maintain the copyright on that code. If you own all the rights to your code, you can fill out an individual CLA. If your employer has any rights to your code, then they also need to fill out a corporate CLA. If you don't know if your employer has any rights to your code, you should ask before signing anything. By default, anyone with an @google.com email address already has a CLA signed for them.
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. Check out our coding conventions for details on making sure your code is in correct style.
5. Submit a pull request for your changes. A project developer will review your work and then merge your request into the project.

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 http://www.apache.org/licenses/LICENSE-2.0.

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.