What is AJAX?

With all the hype about "Ajax web applications", you could be forgiven for assuming Ajax is some radical new plugin, akin to Macromedia Flash. And you would therefore be under the impression that Ajax is out of bounds until you upgrade your "so last month" browser, or at least download the coveted "Ajax plugin".

Good news: You can run Ajax right now. At least, assuming you have a web browser from the past few years - IE, Firefox, Safari, or Opera. Have you seen Google Maps or perhaps GMail? They're both Ajax applications. So are Zuggest and the AjaxPatterns Wiki Demo .

What do they all have in common? All these applications take a great leap forth towards the richness of standard desktop applications. No longer are you forced to wait five seconds for the page to reload every time you click on something. Ajax applications change in real time. They can let you drag boxes around, they can refresh themselves with new information, they can completely re-arrange the page without clearing it. And there's no special plugin required. Ajax is just a style of design, one that milks all the features of modern browsers to produce something that feels less web and more desktop.

Applications can act more like and be developed more like the days of Visual Basic, Delphi, PowerBuilder, C++ with GUI frameworks, etc. Thus, it is 90's GUI features but with a web browser: it strives to meld the best of web and the best of desktop GUI's. Web browser standards were originally designed for e-brochures only. Business forms and other needs were hacked into this e-brochure framework over time and it is clear that this after-thought retrofitting for different purposes has been ugly. Ajax attempts to remedy this.

Some of the characteristics of Ajax applications include:

* Continuous Feel: Traditional web applications force you to submit a form, wait a few seconds, watch the page redraw, and then add some more info. Forgot to enter the area code in a phone number? Start all over again. Sometimes, you feel like you're in the middle of a traffic jam: go 20 metres, stop a minute, go 20 metres, stop a minute ... How many E-Commerce sales have been lost because the user encountered one too many error message and gave up the battle? Ajax offers a smooth ride all the way. There's no page reloads here - you're just doing stuff and the browser is responding. The server is only telling the screen what changed rather than having it redraw the whole screen from scratch.

* Real-Time Updates: As part of the continous feel, Ajax applications can update the page in real-time. Currently, news services on the web redraw the entire page at intervals, e.g. once every 15 minutes. In contrast, it's feasible for a browser running an Ajax application to poll the server every few seconds, so it's capable of updating any information directly on the parts of the page that need changing. The rest of the page is unaffected.

* Graphical Interaction: Flashy backdrops are abundant on the web, but the basic mode of interaction has nevertheless mimicked the 1970s-style form-based data entry systems. Ajax represents a transition into the world of GUI controls visible on present-day desktops. Thus, you will encounter animations such as fading text to tell you something's just been saved, you will be able to drag items around, you will see some static text suddenly turn into an edit field as you hover over it.

* Language Neutrality - Ajax strives to be equally usable with all the popular languages rather than be tied to one language. Past GUI attempts such as VB, Tk, and Swing tended to be married to one specific programming language. Ajax has learned from the past and rejects this notion. To help facilitate this, XML is often used as a declarative interface language.

To prevent any confusion, these things are not characteristic of Ajax:

* Non-Proprietary: "Ajax" is perhaps one of the most common brand names in history, but in context of web design, "Ajax" is neither the name of a company nor a product. It's not even the name of a standard or committee. It's a label for a design approach involving several related technologies.

* Plugin-Based: Ajax applications do not require users to install browser plugins, or desktop software for that matter.

* Browser Specific: As long as the user is working with a relatively recent, mainstream, browser (say 2001+), the application should work roughly the same way. Browser-specific applications somewhat defeat the purpose of Ajax.