This is the first in my series of explainer posts. Ajax is the talk of the Web 2.0 world at the moment; it’s seen by many as the ‘must have’ feature of any web service, and is described by others as an over-hyped, over-used technology. But what is it? Well, it stands for Asynchrous Javascript and XML, and is essentially a way in which a website can update what you see on it without you having to refresh the page. That makes it perfect for rich web applications - websites which are aiming to act as much like traditional desktop applications as possible.

A great example of the use of Ajax, compared to traditional techniques would be Gmail and Hotmail. Gmail makes great use of Ajax, meaning that if someone sends you an email while you are looking at your inbox, it appears in your inbox without you refreshing the page. Or if you archive a message, it disappears from your inbox without refreshing. This allows you to work much faster, because you don’t have to wait after every action, as you did in earlier webmail services, like Hotmail. In Hotmail, every time you change a view you have to refresh the page. The next version of Hotmail (currently in beta version) is Windows Live Mail, and that uses lots of Ajax to create an experience as much like a conventional program such as Outlook as possible. Ajax is important because it is one of the major fuels of Web 2.0. Without Ajax, no-one would use services like Writely, because it would be so inefficient, and the experience so inferior to using a program such as Microsoft Word.

For further specific information about how Ajax works, see Wikipedia. For examples of Ajax websites, just read Techcrunch, or have a look at this use of Ajax to power a remote desktop.