Web 2.0 came on internet with many new web technologies. Ajax is perhaps the most important and popular technologies which helped us to build the second version of world wide web. Today I will discuss about Ajax and its implications on an internet application. This is first article in new series called “What is” which I have introduced on my blog to discuss basics of commonly used technologies on internet. Ajax is basically asynchronous Java Script and XML. It is a web 2.0 web technology used for creating interactive web applications or rich Internet applications. With Ajax, web applications can retrieve data from the server asynchronously in the background without refreshing the existing page. Data are retrieved using the XMLHttpRequest object or through the use of Remote Scripting in browsers that do not support it. Earlier before the evolution of Ajax on internet, webmasters make use of iFrames for implementing displaying the changed content without completely refreshing the whole page.

In most of the cases, the pages on a website consist of much content that is common between them. In traditional methods, that content would have to be reloaded on every request from external web service or database. However, using Ajax, a web application can request only the content that needs to be updated, thus we can easily save the bandwidth of the hosting server.

With the use of asynchronous requests, we can have client’s Web browser UI to be more interactive and to respond quickly to inputs, and sections of pages can also be reloaded individually. Users may perceive the application to be faster or more responsive, even if the application has not changed on the server side.

However there is one important disadvantage of using Ajax. Any user whose browser does not support Ajax or Java Script, or simply has Java Script disabled, will not be able to use the power of Ajax. Similarly, devices such as mobile phones, PDAs, and screen readers may not have support for Java Script or the XMLHttpRequest object. Still R & D is going on in this area.