Getting Started with the Closure Compiler Application
The Hello World of the Closure Compiler Application
The Closure Compiler application is a Java command-line utility that compresses, optimizes, and looks for mistakes in your JavaScript. To try out the Closure Compiler application with a simple JavaScript program, follow the steps below.
To work through this exercise you need the Java Runtime Environment version 6.
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Download the Closure Compiler package
Create a working directory called
closure-compiler.Download the Closure Compiler compiler.jar file and save it in
closure-compiler. -
Create a JavaScript file
Create a file named
hello.jscontaining the following JavaScript:// A simple function. function hello(longName) { alert('Hello, ' + longName); } hello('New User');
Save this file in the
closure-compilerdirectory. -
Compile the JavaScript file
Run the following command from the
closure-compilerdirectory:java -jar compiler.jar --js hello.js --js_output_file hello-compiled.js
This command creates a new file called
hello-compiled.js, which contains the following JavaScript:function hello(a){alert("Hello, "+a)}hello("New User");
Note that the compiler has stripped comments, whitespace and an unnecessary semi-colon. The compiler has also replaced the parameter name
longNamewith the shorter namea. The result is a much smaller JavaScript file.To confirm that the compiled JavaScript code still works correctly, include
hello-compiled.jsin an HTML file like this one:<html> <head><title>Hello World</title></head> <body> <script src="hello-compiled.js"></script> </body> </html>
Load the HTML file in a browser, and you should see a friendly greeting!
Next Steps
This example illustrates only the most simple optimizations performed by the Closure Compiler. To learn more about the compiler's capabilities, read Advanced Compilation and Externs.
To learn more about other flags and options for the Closure Compiler, execute the jar with the --help flag:
java -jar compiler.jar --help
