4.5. Advantages to Using a Library

As with any other technology, you can grab off-the-shelf components to handle implementing AJAX instead of writing all the code yourself. This can help reduce the changes to your overall development cycle, or it can cause more changes than starting everything from scratch. This effect depends not only on the quality of the library, but also on its fit into your current processes and development style. If you can find a library that fits your needs, it will help reduce the changes wrought by adding AJAX to your toolbox. The largest advantage comes from the library's ability to hide the hard parts of JavaScript development (cross-browser support, communications between different languages, and visual effects), but you can also make gains just from following the best practices of someone else instead of having to spend time figuring out all the new rules on your own.

When developers first take a look at AJAX, they may think it's a simple technology with enough support from major browsers that they can take off coding from scratch. This approach ignores the fact that even the major browsers have implementation differences around which you're going to need to work. If your approach is too simplistic, you can end up in a position where it's impossible to work around various browser bugs without recoding large amounts of your application or Web site. The better that the basic browser primitives are hidden, the easier it is to plug in new compatibility techniques. These techniques range from using IFrames on older browsers to implementing new JavaScript API elements that haven't yet been added to browsers.

An AJAX library needs to cover basic communications aspects, allowing you to make asynchronous requests to your server from all the browsers you need to support. Depending on your choices, you will also need some other features; if you need eXtensible Stylesheet Language Transformation (XSLT) support, you'll need a library that hides the differences between the Firefox and IE implementations. You may need code that encodes data in a specific type to be sent to your server; this can be any format, from JavaScript Object Notation (JSON) to Extensible Markup Language (XML). It is also useful to support the tasks often used in conjunction with basic AJAX development, including drag-and-drop, visual effects, dynamic positioning, and DOM manipulation.

A good library helps hide the problematic areas of JavaScript, adding in compatibility between different browsers while offering a clean, easy-to-use API. It also exposes its feature set without making you learn every inch of its API. Drag-and-drop is a great feature, but if it gets in the way of something more basic, then it's making tradeoffs that aren't useful to a developer. No matter the source of your AJAX library, make sure it meets your needs in a clean well-encapsulated manner. Don't be afraid to mix and match libraries, taking the best features from each one, but remember that each library has a cost in download size, and not every environment will be a high-bandwidth local network.