Google Closure Compiler

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

The easiest way to install the compiler is with NPM or Yarn:

yarn global add google-closure-compiler
# OR
npm i -g google-closure-compiler

The package manager will link the binary for you, and you can access the compiler with:

google-closure-compiler

This 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;

Downloading from Maven Repository

A pre-compiled release of the compiler is also available via Maven.

Basic usage

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.js

We 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.js

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.

NodeJS API

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.

Compiling Multiple Scripts

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.js

You 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.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.

Getting Help

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

Building the Compiler

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.

Installing Bazelisk

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.

Building from a terminal

$ bazelisk build //:compiler_uberjar_deploy.jar
# OR to build everything
$ bazelisk build //:all

Testing from a terminal

Tests can be executed in a similar way. The following command will run all tests in the repo.

$ bazelisk test //:all

There 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_file

Building from an IDE

See Bazel IDE Integrations.

Running

Once 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]

Running using Eclipse

Open the class src/com/google/javascript/jscomp/CommandLineRunner.java or 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.

Contributing

Contributor code of conduct

However you choose to contribute, please abide by our code of conduct to keep our community a healthy and welcoming place.

Reporting a bug

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.

Suggesting a feature

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.

Submitting patches

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.

Closure Compiler License

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.

Dependency Licenses

Rhino

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.

Args4j

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

Guava Libraries

URL	https://github.com/google/guava
Version	31.0.1
License	Apache License 2.0
Description	Google's core Java libraries.
Local Modifications	None

JSR 305

URL	https://github.com/findbugsproject/findbugs
Version	3.0.1
License	BSD License
Description	Annotations for software defect detection.
Local Modifications	None

JUnit

URL	http://junit.org/junit4/
Version	4.12
License	Common Public License 1.0
Description	A framework for writing and running automated tests in Java.
Local Modifications	None

Protocol Buffers

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

RE2/J

URL	https://github.com/google/re2j
Version	1.3
License	New BSD License
Description	Linear time regular expression matching in Java.
Local Modifications	None

Truth

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

Ant

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

GSON

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

Node.js Closure Compiler Externs

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.

nvq247/closure-compiler