WebReference.com - Part 3 of chapter 5 from Creating Applications with Mozilla. From O'Reilly (3/4).

There are two ways to use JavaScript in the third, deepest level of application programming. The first is to organize your JavaScript into libraries so your functions can be reused, distributed, and perhaps collaborated upon.

The second way is to write a JavaScript component, create a separate interface for that component, and compile it as an XPCOM component whose methods and data can be accessed from XPConnect (using JavaScript). This kind of application programming is described in Chapter 8, which includes examples of creating new interfaces, implementing them in JavaScript or C++, and compiling, testing, and using the resulting component in the Mozilla interface.

This section introduces the library organization method of JavaScript application programming. The JSLib code discussed here is a group of JavaScript libraries currently being developed by Mozilla contributors and is especially useful for working with the XPFE and other aspects of the Mozilla application/package programming model. When you include the right source files at the top of your JavaScript and/or XUL file, you can use the functions defined in JSLib libraries as you would use any third-party library or built-in functions. You may even want to contribute to the JSLib project yourself if you think functionality is missing and as your Mozilla programming skills grow.

The open source JSLib project makes life easier for developers. The JSLib package implements some of the key XPCOM components just discussed and wraps them in simpler, JavaScript interfaces, which means that you can use the services of common XPCOM components without having to do any of the instantiation, interface selection, or glue code yourself. Collectively, these interfaces are intended to provide a general-purpose library for Mozilla application developers. To understand what JSLib does, consider the following short snippet from the JSLib source file jslib/io/file.js, which implements a close( ) function for open file objects and provides a handy way to clean up things when you finish editing a file in the filesystem.

/********************* CLOSE ********************************
* void close( )                                              *
*                                                           *
* void file close                                           *
* return type void(null)                                    *
* takes no arguments closes an open file stream and         *
* deletes member var instances of objects                   *
*   Ex:                                                     *
*     var p='/tmp/foo.dat';                                 *
*     var f=new File(p);                                    *
*     fopen( );                                              *
*     f.close( );                                            *
*                                                           *
*   outputs: void(null)                                     *
************************************************************/
File.prototype.close = function( )
{
/***************** Destroy Instances *********************/
if(this.mFileChannel)   delete this.mFileChannel;
if(this.mInputStream)   delete this.mInputStream;
if(this.mTransport)     delete this.mTransport;
if(this.mMode)          this.mMode=null;
if(this.mOutStream) {
this.mOutStream.close( );
delete this.mOutStream;
}
if(this.mLineBuffer)     this.mLineBuffer=null;
this.mPosition           = 0;
/***************** Destroy Instances *********************/
return;
}

To use the close method as it's defined here, import the file.js source file into your JavaScript, create a file object (as shown in the examples below), and call its close( ) method.

To use the JavaScript libraries, install the JSLib package in Mozilla. The package is available as a tarball, a zip file, or as CVS sources. The easiest way to obtain it is to install it from the Web using Mozilla's XPInstall technology, described in Chapter 6.