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.
The easiest way to install the compiler is with NPM or Yarn:
yarn global add google-closure-compiler
# OR
npm i -g google-closure-compilerThe package manager will link the binary for you, and you can access the compiler with:
google-closure-compilerThis starts the compiler in interactive mode. Type:
var x = 17 + 25;Hit Enter, then Ctrl+Z (on Windows) or Ctrl+D (on Mac/Linux), then Enter
again. The Compiler will respond with the compiled output (using SIMPLE mode
by default):
var x=42;A pre-compiled release of the compiler is also available via Maven.
The Closure Compiler has many options for reading input from a file, writing output to a file, checking your code, and running optimizations. Here is a simple example of compressing a JS program:
google-closure-compiler --js file.js --js_output_file file.out.jsWe get the most benefit from the compiler if we give it all of our source
code (see Compiling Multiple Scripts), which
allows us to use ADVANCED optimizations:
google-closure-compiler -O ADVANCED rollup.js --js_output_file rollup.min.jsNOTE: The output below is just an example and not kept up-to-date. The Flags and Options wiki page is updated during each release.
To see all of the compiler's options, type:
google-closure-compiler --help--flag |
Description |
|---|---|
--compilation_level (-O) |
Specifies the compilation level to use.
Options: BUNDLE, WHITESPACE_ONLY,
SIMPLE (default), ADVANCED
|
--env |
Determines the set of builtin externs to load.
Options: BROWSER, CUSTOM.
Defaults to BROWSER.
|
--externs |
The file containing JavaScript externs. You may specify multiple |
--js |
The JavaScript filename. You may specify multiple. The flag name is
optional, because args are interpreted as files by default. You may also
use minimatch-style glob patterns. For example, use
--js='**.js' --js='!**_test.js' to recursively include all
js files that do not end in _test.js
|
--js_output_file |
Primary output filename. If not specified, output is written to stdout. |
--language_in |
Sets the language spec to which input sources should conform.
Options: ECMASCRIPT3, ECMASCRIPT5,
ECMASCRIPT5_STRICT, ECMASCRIPT_2015,
ECMASCRIPT_2016, ECMASCRIPT_2017,
ECMASCRIPT_2018, ECMASCRIPT_2019,
STABLE, ECMASCRIPT_NEXT
|
--language_out |
Sets the language spec to which output should conform.
Options: ECMASCRIPT3, ECMASCRIPT5,
ECMASCRIPT5_STRICT, ECMASCRIPT_2015,
ECMASCRIPT_2016, ECMASCRIPT_2017,
ECMASCRIPT_2018, ECMASCRIPT_2019,
STABLE
|
--warning_level (-W) |
Specifies the warning level to use.
Options: QUIET, DEFAULT, VERBOSE
|
See the Google Developers Site for documentation including instructions for running the compiler from the command line.
You can access the compiler in a JS program by importing
google-closure-compiler:
import closureCompiler from 'google-closure-compiler';
const { compiler } = closureCompiler;
new compiler({
js: 'file-one.js',
compilation_level: 'ADVANCED'
});This package will provide programmatic access to the native Graal binary in most cases, and will fall back to the Java version otherwise.
Please see the closure-compiler-npm repository for documentation on accessing the compiler in JS.
If you have multiple scripts, you should compile them all together with one compile command.
google-closure-compiler in1.js in2.js in3.js --js_output_file out.jsYou can also use minimatch-style globs.
# Recursively include all js files in subdirs
google-closure-compiler 'src/**.js' --js_output_file out.js
# Recursively include all js files in subdirs, excluding test files.
# Use single-quotes, so that bash doesn't try to expand the '!'
google-closure-compiler 'src/**.js' '!**_test.js' --js_output_file out.jsThe 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.
- Post in the Closure Compiler Discuss Group.
- Ask a question on Stack Overflow.
- Consult the FAQ.
To build the compiler yourself, you will need the following:
| Prerequisite | Description |
|---|---|
| Java 8 or later | Used to compile the compiler's source code. |
| Git | Used by Bazel to download dependencies. |
| Bazelisk | Used to build the various compiler targets. |
Bazelisk is a wrapper around Bazel that dynamically loads the appropriate version of Bazel for a given repository. Using it prevents spurious errors that result from using the wrong version of Bazel to build the compiler, as well as makes it easy to use different Bazel versions for other projects.
Bazelisk is available through many package managers. Feel free to use whichever you're most comfortable with.
Instructions for installing Bazelisk.
$ bazelisk build //:compiler_uberjar_deploy.jar
# OR to build everything
$ bazelisk build //:allTests can be executed in a similar way. The following command will run all tests in the repo.
$ bazelisk test //:allThere are hundreds of individual test targets, so it will take a few minutes to run all of them. While developing, it's usually better to specify the exact tests you're interested in.
bazelisk test //:$path_to_test_fileOnce the compiler has been built, the compiled JAR will be in the bazel-bin/
directory. You can access it with a call to java -jar ... or by using the
package.json script:
# java -jar bazel-bin/compiler_uberjar_deploy.jar [...args]
yarn compile [...args]- Open the class
src/com/google/javascript/jscomp/CommandLineRunner.javaor create your own extended version of the class. - Run the class in Eclipse.
- See the instructions above on how to use the interactive mode - but beware of the bug regarding passing "End of Transmission" in the Eclipse console.
However you choose to contribute, please abide by our code of conduct to keep our community a healthy and welcoming place.
- 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
- Look through the list of compiler assumptions.
- If you still think you have found a bug, make sure someone hasn't already reported it. See the list of known issues.
- 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.
- Consult the FAQ to make sure that the behaviour you would like isn't specifically excluded (such as string inlining).
- Make sure someone hasn't requested the same thing. See the list of known issues.
- Read up on what type of feature requests are accepted.
- Submit your request as an issue.
- 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.
- To make sure your changes are of the type that will be accepted, ask about your patch on the Closure Compiler Discuss Group
- Fork the repository.
- Make your changes. Check out our coding conventions for details on making sure your code is in correct style.
- 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.
| Code Path |
src/com/google/javascript/rhino, test/com/google/javascript/rhino
|
| URL | https://developer.mozilla.org/en-US/docs/Mozilla/Projects/Rhino |
| Version | 1.5R3, with heavy modifications |
| License | Netscape Public License and MPL / GPL dual license |
| Description | A partial copy of Mozilla Rhino. Mozilla Rhino is an implementation of JavaScript for the JVM. The JavaScript parse tree data structures were extracted and modified significantly for use by Google's JavaScript compiler. |
| Local Modifications | The packages have been renamespaced. All code not relevant to the parse tree has been removed. A JsDoc parser and static typing system have been added. |
| URL | http://args4j.kohsuke.org/ |
| Version | 2.33 |
| License | MIT |
| Description | args4j is a small Java class library that makes it easy to parse command line options/arguments in your CUI application. |
| Local Modifications | None |
| URL | https://github.com/google/guava |
| Version | 31.0.1 |
| License | Apache License 2.0 |
| Description | Google's core Java libraries. |
| Local Modifications | None |
| URL | https://github.com/findbugsproject/findbugs |
| Version | 3.0.1 |
| License | BSD License |
| Description | Annotations for software defect detection. |
| Local Modifications | None |
| URL | http://junit.org/junit4/ |
| Version | 4.13 |
| License | Common Public License 1.0 |
| Description | A framework for writing and running automated tests in Java. |
| Local Modifications | None |
| URL | https://github.com/google/protobuf |
| Version | 3.0.2 |
| License | New BSD License |
| Description | Supporting libraries for protocol buffers, an encoding of structured data. |
| Local Modifications | None |
| URL | https://github.com/google/re2j |
| Version | 1.3 |
| License | New BSD License |
| Description | Linear time regular expression matching in Java. |
| Local Modifications | None |
| URL | https://github.com/google/truth |
| Version | 1.1 |
| License | Apache License 2.0 |
| Description | Assertion/Proposition framework for Java unit tests |
| Local Modifications | None |
| URL | https://ant.apache.org/bindownload.cgi |
| Version | 1.10.11 |
| License | Apache License 2.0 |
| Description | Ant is a Java based build tool. In theory it is kind of like "make" without make's wrinkles and with the full portability of pure java code. |
| Local Modifications | None |
| URL | https://github.com/google/gson |
| Version | 2.9.1 |
| License | Apache license 2.0 |
| Description | A Java library to convert JSON to Java objects and vice-versa |
| Local Modifications | None |
| Code Path | contrib/nodejs |
| URL | https://github.com/dcodeIO/node.js-closure-compiler-externs |
| Version | e891b4fbcf5f466cc4307b0fa842a7d8163a073a |
| License | Apache 2.0 license |
| Description | Type contracts for NodeJS APIs |
| Local Modifications | Substantial changes to make them compatible with NpmCommandLineRunner. |