Ajax (also, AJAX), short for Asynchronous JavaScript and XML, is a group of interrelated web development techniques used to create interactive web applications. Ajax can improve response time by communicating with the server without full page requests. The result  is a rich interface and better quality applications. A simple example of Ajax is the ‘Suggest’ feature in Google – suggestions are displayed as you type in your query in the search box.

Why use Ajax?

Bandwidth savings: In applications that have a significant part of each page containing content that is identical in multiple page requests, using Ajax to update only the relevant parts of a page can bring about a significant savings in bandwidth requirements. The savings is generally dependent on the complexity of the website. Even a 10% saving in bandwidth will be significant when considering data intensive web applications (like one requiring display of rich, interactive maps and graphs) or a bandwidth constrained web application.

Time savings: Ajax can also bring increase the efficiency of using a web application. Let’s say you only want to see a list of refreshed news items on the website. The time saved by making a request only for the news items instead of the entire page is significant when accumulated over a period.

Improved responsiveness: Ajax can bring about a better and uninterrupted work flow, thus increasing productivity. Ajax also lets you work on the page while information is being retrieved in the background for a part of it.

These three factors can significantly improve overall business productivity.

One drawback with Ajax is that using the ‘Back’ button on the browser may not always take the user to the previous logical operation that they had performed, but to the previous page in the browser history, since an Ajax request is not a page request. Bookmarking will also not work. Recent releases of browsers have exposed functionality that allows developers to manipulate the browser history to show the correct operations performed by users on an Ajax enabled page, but not all web applications have incorporated this feature. Also, since the screen content is being updated dynamically, the changes may not be detected by accessibility tools.

Another is that, in many cases, complex JavaScript is required to make use of the full potential that Ajax offers, and JavaScript with high complexity is not the easiest of things to understand.

Ajax has been around for quite some time now, and has been playing a significant part in improving the interactivity of web applications. With the rich experience it can offer users, it is also one of the enablers of Web 2.0 (note: Ajax itself is not Web 2.0), and we can probably expect to see it around for quite some time to come.

References: http://www.helium.com/items/49433-advantages-and-disadvantages-of-ajax; http://www.webperformanceinc.com/library/reports/AjaxBandwidth/; http://www.ibm.com/developerworks/web/library/wa-aj-perform/index.html