Ajax is a common term in Web 2.0, but what does it actually mean? It actually describes a collection of existing technologies, what’s new is the way they work together. Ajax allows users to keep interacting with a webpage as resources update in the background, so there is no waiting for a page to reload.

Websites such as Google Maps and Zimbra aim to replicate the experience of using a desktop application. Adaptive Path’s Jesse James Garrett is credited with first coining the term ‘Ajax’ in 2005 in an online essay. Ajax stands for ‘Asynchronous Javascript and XML’, and Garrett claimed it came in five parts:

• XHTML and CSS
• DOM
• XML
• XMLHttpRequest
• JavaScript – which ties the other components together

Despite this list, there are no strict rules to what is or isn’t Ajax. For example, using innerHTML rather than DOM or using HTML instead of XML are both acceptable alternatives. Some prefer JavaScript tags to XMLHttpRequest, while others prefer to use Flash, SVG or XUL instead of XHTML and CSS. Developers need to choose elements based on what’s best for their application, for reasons such as performance, accessibility, browser support and standards compliance.

All these design decisions come into the equation when building a new website, and can effect which technologies you choose to employ. Despite the variety of options, all Ajax projects rely on JavaScript to tie the various parts together