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 7.

Download the Closure Compiler package

Create a working directory called closure-compiler .

Download the most recently released JAR file from the Maven repository , and save it in closure-compiler .

Create a JavaScript file

Create a file named hello.js containing the following JavaScript:

 // A simple function. 
 function 
  
 hello 
 ( 
 longName 
 ) 
  
 { 
  
 alert 
 ( 
 ' 
 Hello 
 , 
  
 ' 
  
 + 
  
 longName 
 ); 
 } 
 hello 
 ( 
 ' 
 New 
  
 User 
 ' 
 );

Save this file in the closure-compiler directory.

Compile the JavaScript file

Run the following command from the closure-compiler directory:
```
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 longName with the shorter name a . The result is a much smaller JavaScript file.

To confirm that the compiled JavaScript code still works correctly, include hello-compiled.js in 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

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The Hello World of the Closure Compiler Application

Next Steps

Getting Started with the Closure Compiler Application