AJAX - The Complete Reference

178 Part II: Applied Ajax^

it aim to do many things and none of them exceedingly well? Finally, is the library well

supported? In other words, is this library likely to be supported over the course of time, or are

you going to be stuck maintaining it yourself?

We also must address a somewhat contentious reason that JavaScript libraries are built: to

significantly change how JavaScript tends to be written. It is a bit disturbing to see libraries

make statements like, “making JavaScript suck less” as a design goal, especially when the less

“sucking” effect is often accomplished by trying to make JavaScript act more like some other

language. It is particularly troubling when these libraries override built-in aspects of the

language, thus making it quite difficult to intermix code from one library and another.

If you take the time to evaluate many libraries, it will also become very clear that some

authors want JavaScript to act more like other languages such as Ruby, Python, Java, or even

more like a Lisp-style language like ML. Interestingly, it is the raw dynamic power of

JavaScript that allows these well-intentioned folks to tersely implement their other language-

flavored approaches to JavaScript. If the JavaScript language really was so underpowered,

they simply wouldn’t be able to accomplish this feat so easily.

It is our strong opinion that programmers should attempt to work with JavaScript and

program it as JavaScript, not some other language. You may disagree with that opinion and

find the near meta-language approach of JavaScript mimicking aspects of a particular

Library Category Description

Ajax communications Minimally a librar y will wrap an XHR object, but good libraries

should address timeouts, retries, and error issues. Advanced

libraries may add support for histor y management, offline storage,

and persistence.

DOM utilities A librar y may provide methods to make working with DOM trees

easier. Extensions like getElementsByClassName() are

commonplace, but some libraries may have complex content

selection systems that rely on CSS or Xpath syntax.

Event management A significant headache for JavaScript developers is addressing

cross-browser event concerns. Because of poor event management

and long stays on the same page, Ajax applications that do not

manage events properly may leak memor y. Given this situation,

many libraries provide cross-browser and, hopefully, leak-proof

event handling functions.

Utility functions A decent Ajax librar y should provide functions to address the

serialization of form data. Other data format encoding and

decoding such as dealing with JSON is also commonly found.

UI widgets and effects Higher-level libraries may provide widgets that both encapsulate UI

and tie in with lower-level Ajax and DOM facilities. These libraries

also often provide basic animation and visual effects that may be

useful when building rich inter faces. However, in this discussion,

we will be careful not to overemphasize the UI and effect aspect of

libraries as it starts to move out of the Ajax specific realm and into

inter face design.

TABLE 5-1 Common Ajax-Focused JavaScript Librar y Features