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AJAX is the buzzword of the moment among web developers, so much so that you could be sick of introductions to AJAX by now (if that's the case, skip down to "The Chat Web Page"). AJAX is a technology that is hotly debated from many angles, but it has stuck because it encapsulates something that is new from a user's perspective. The functionally that is newly available to all web users is "in-page replacement": the ability for a web page to change using data from a web server without totally redrawing itself. This functionality has been around in Mozilla and Internet Explorer for a while, but it is only recently that Safari and Konqueror users have been able to join in.

It is this ability to have web pages that update dynamically that is changing the way users interact with the web. For example:

Activity	Old Style	AJAX Style
Scrolling in a mapping website	Click on a right arrow to refresh whole page.	Drag map area to the right--and watch the map scroll, like Google Maps.
Looking up a word in a dictionary	Enter the word, and click Submit to see a definition for that word.	Begin typing the word, see possible matches as you type and the definitions as soon as you finish typing, like ObjectGraph Dictionary.
Interacting in online forum	Type message, click Submit, regularly click "check new messages".	Type messages, and wait as new replies appear automatically without needing your interaction. We will create a site like this in this article.
Filling out form with a number of fields	Visit a number of pages of a "wizard," getting error messages about invalid fields.	Fill out a form that reports on errors as you type, and can dynamically add data (like filling in full address details from a zip code) without needing a slow page refresh.

AJAX isn't the best acronym in the world: it stands for Asynchronous JavaScript and XML. This does nothing to describe the benefits to a user: the technology behind it does not have to be asynchronous, and the best implementations don't necessarily use XML, either. However, the buzzword has stuck so we are better off going with the flow now.

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