Learning PHP, MySQL, and JavaScript

What Is Ajax?

The beginnings of Ajax as used today started with the release of Internet Explorer 5 in 1999, which introduced a new ActiveX object, XMLHttpRequest. ActiveX is Microsoft’s technology for signing plug-ins that add additional software to your computer. Other browser developers later followed suit, but rather than using ActiveX, they all implemented the feature as a native part of the JavaScript interpreter.

However, even before then, an early form of Ajax had already surfaced that used hidden frames on a page that interacted with the server in the background. Chat rooms were early adopters of this technology, using it to poll for and display new message posts without requiring page reloads.

Nowadays, though, XMLHttpRequest is the way to go, and there have been numerous frameworks written to simplify its use. In fact, Chapter 19 introduces the powerful Yahoo! User Interface (YUI) JavaScript framework. But first, let’s see how to implement Ajax with raw JavaScript. This will help you understand what your program and the browser are doing as you code with YUI or another library of your choice.