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Google的js压缩与优化工具: Getting Started with the Closure Compiler Application

2012-03-14 02:02 676 查看

https://developers.google.com/closure/compiler/docs/gettingstarted_app

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.

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.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

. 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>
<scriptsrc="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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