How To Use Google Closure Compiler to Compress JavaScript code

Closure Compiler is a JavaScript checker and optimizer. It checks syntax, variable references, types, and warns about common JavaScript pitfalls. This article shows you how to use it to compress JavaScript code. This makes our code run faster, smaller in size, etc.

1. Installation

You are able to download it on Closure Compiler site or use this direct link compiler-latest.zip.

Because it is written in Java, so ensure that you have installed JDK 7+ on your machine before running it.

2. Usage

Let’s assume you want to compress myapp.js file.

Now run the following command:

java -jar closure-compiler.jar --js myapp.js --create_source_map myapp.min.js.map --js_output_file myapp.min.js

The command will create you the below new files:

myapp.min.js
myapp.min.js.map

If you want to learn more about other flags and options for the Closure Compiler, execute the jar with the --help flag:

java -jar closure-compiler.jar --help

3. Q&A

Q: I am getting the below warning while compiling my javascript file:

ERROR - "arguments.callee" cannot be used in strict mode

A: That warning occurred because arguments.callee is deprecated in ES5. So to solve that, you should add the --warning_level=QUIET option to the command.