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By Ron Bradburn

I'm sure some of you have seen or heard the term AJAX before. No, it’s not the stuff we use to clean our sinks, it's a combination of web based technologies which enables your web pages to do things you didn't think were possible. AJAX stands for Asynchronous Javascript and XML. It involves the combination of HTML or XHTML and CSS for presentation, javascript and DOM (Document Object Model) for manipulating dynamic content, and the XMLHttpRequest object. This object enables background http requests to remote servers, allowing you to send and receive data from a remote source without reloading the current page. The transfers can occur asynchrounously, meaning your code can do other tasks as it waits for results from the server. The benefits of AJAX are tremendous. For one, a web site that relies on heavy graphics usage can be optimized so a user only has to load a page once. After it is loaded, any transactions like user login, submitting shopping cart data, etc can all happen in the background without ever reloading the page. This can reduce bandwith usage and opens up new ways to track your users’ movement throughout your website. You can maintain user state very easily without having to code difficult scripts that constantly read and store attributes as the user goes through a series of submission forms.

AJAX is supported by many of the most popular web browsers available including Microsoft Internet Explorer, Mozilla Firefox, SeaMonkey, Opera, Konquerer, and Apple Safari.

As you type text in the search box, a popup will show up with topics related to your search query. This popup gets its data remotely via XMLHttpRquest querying Google for past searches, and a bit of DHTML to generate the popup and display it on the page. This is just a very small example. AJAX can be used for much more, like interactive shopping carts, web-based GUI interfaces that can populate list boxes on the fly based on user input, etc. Google Maps and Gmail are also AJAX applications, updating the web page on the fly as you scroll around a map or read up on your gmail conversations.