Tech Primer

AJAX (Asynchronous JavaScript & XML)

What is AJAX?

AJAX stands for Asynchronous JavaScript and XML (Extensible Markup Language). It is used in Web development for creating interactive Web applications. The technology combines HTML, XHTML (Extensible Hyper Text Markup Language) and CSS (Cascading Style Sheets) to present information. AJAX works in Web browsers that support DHTML (Dynamic Hyper Text Markup Language) and LAMP. LAMP can be understood as

L - Linux Operating System,
A - Apache (Web server),
M - My SQL database, and
P - Perl, PHP or Python scripting language.

Mozilla, Firefox, Internet Explorer 6, Opera 7 (included in all updated version like Opera 8), Konqueror & Safari support this technology.

How does AJAX work?

An AJAX application sends a request to the Web server to retrieve the data needed using SOAP (Simple Object Access Project) and other XML-based Web services. This form of application reduces data interchange between the Web server and browser. In early 2005, a number of events led to AJAX becoming popular. Google is considered to be a pioneer of asynchronous technology. It incorporated it in Gmail (Google mail), Google groups and Google maps. Some other search engines (besides google.com) have also considered the AJAX technology including www.flickr.com and www.a9.com. A few blogs like www.kottke.org and www.colr.org have also embraced this technology.

Is AJAX new?

Reading about this technology today may lead us to conclude that AJAX is something new. The truth is that it has been around for years under various names like JavaScript Remote Scripting, Remote Scripting with I-frame technology, and JPSpan.

Are there any drawbacks to this technology?

AJAX has a few disadvantages. One is that using the back button on a browser does not work well with JavaScript. The use of the back button is considered vital, and this is one of the reasons why we cannot have pure JavaScript Web applications. AJAX enables users to structure interesting and impressive applications. Additional code-work means increasing the workload of a browser, and this requires a more powerful CPU. The problem of managing a heavy workload has not disappeared completely. AJAX refers to coding through asynchronous messages. There are times when these messages pop up unexpectedly, creating confusion.

Which are the competing technologies?

Some competing technologies are Flash, XAML, XUL and Laszlo. Flash is an animated graphics technology enabling users to generate flash files. Macromedia Flash Mix, Freehand, etc. generate flash files that can be viewed in Web browsers using a plug-in or standalone viewer. The flash files use the .swf (small web format) extension. These .swf files are widely used on the net as they are space-efficient. Another technology is XAML (Extensible Application Markup Language, (pronounced as “zammel”). This language is developed by Microsoft. Use of XML requires no support from any other language like HTML, Flash or PDF (Portable Document Format). XAML works well for Web and .Net applications. Then there is XUL (XML User Interface Language), pronounced as “zool,” a Mozilla XML-based User interface Language. The language enables users to build rich cross-platform applications that can run when connected or disconnected to the Internet.

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— Garima Grover