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Asynchronous Javascript and XML or AJAX is currently the hot and trendy technology of the moment. Google pushed it onto the world stage though archrival Microsoft did early work in the underpinnings of the technology. Actually, it isn’t so much a technology as a combination of existing technologies. So, what is AJAX and why is it so trendy right now?

AJAX is a combination of existing web-based technologies designed to modify the browser-based user interface. It essentially makes the browser user-interface behave more like a seamlessly than a form-based application. Traditionally, a web application uses forms – for example, you fill in your name, address, credit card number, etc. and click the “submit” button. This sends the form data to a web server to process and you get a follow-on screen either saying “thank you” or “you forgot to put in the expiration date”. It’s a pretty simplistic model; the user interface is somewhat jerky in transitions but most people have gotten used to it.

AJAX uses a combination of javascript (a scripting engine that is actually executed inside your PC browser), xml, and background http requests to create a user interface that presents a smoother application behavior to the user while performing background processing and web requests. The result is an interface that appears to react immediately and without abrupt, whole-screen changes.

Google put this technology into the mainstream with the highly popular Gmail. Microsoft is now following suit with their Hotmail interface and many other web-based companies are also racing to implement AJAX. For those of you considering adding this technology to your web businesses, take a moment to think about the downsides. AJAX has several downsides (all technologies do) so think about what they mean before sinking a lot of resources into it.

First, AJAX relies on javascript to operate in browsers and not all browsers support javascript in the same way or with the same versions. Therefore, your developers will need to test AJAX application carefully on target browsers and versions. You will be limiting the number of browsers that support your web application properly; web-forms are simple but well supported on just about all browsers.

Second, AJAX tends to break the browser’s “back” button. Because the browser is presenting data within a javascript engine while also performing lookups, requests, and background processing, using the “back” button on the browser ends up putting the application into some strange and often unknown state. Again, while simplistic, most people have gotten used to begin able to go “back” when they get confused.

Finally, AJAX requires a more complex programming approach for your developers. They need to keep track of component states at the client side, presentation logic, and active application request logic.

AJAX is an interesting technology and one of the first reasonably well implemented applications of a richer and smoother user interface after the failure of Java applets. It’s now proven in some very popular and widely used applications too (e.g., Gmail, Hotmail). If your business would benefit from a slicker interface, your users are knowledgeable, and you understand the development needs, then AJAX could be right for you.

Lee Le Clair is the CTO at Ephibian. His Tech Talk column appears the third week of each month in Inside Tucson Business