Some PHP programmers would argue that the most important use of JavaScript is to provide Ajax functionality to your programs. Whether or not you agree, Ajax is certainly a central part of today's Internet. Standing for Asynchronous JavaScript and XML, Ajax is really a misnomer because it often has little to do with XML as it can handle all manner of file types. However, when Microsoft first introduced the feature in Internet Explorer 5 (back in 1999) they named the new ActiveX object XMLHttpRequest, and the name has stuck ever since. This plug-in is the pure JavaScript side of the Ajax equation, which requires two programs, one on the client computer and one on the server, to interact with each other.

The Figure shows it being used (along with the following JavaScript plug-in, Post Request), to load the main pluginphp.com web page inside a pair of <div>…</div> tags.

Using Ajax techniques you can load new elements into a page in the background