The Origins of AJAX

Recent examples of AJAX usage include Gmail and  Flickr. It is largely due to these and other prominent sites that AJAX has become popular only relatively recently – the technology has been available for some time. One precursor was dynamic HTML (DHTML), which twinned HTML with CSS and JavaScript but suffered from cross-browser compatibility issues. The major technical barrier was a common method for asynchronous data exchange, many variations are possible, such as the use of an "iframe" for data storage or JavaScript Object Notation for data transmission, but the wide availability of the XMLHttpRequest object has made it a popular solution. AJAX is not a technology, rather, the term refers to a proposed set of methods using a number of existing technologies. As yet, there is no firm AJAX standard, although the recent establishment of the Open AJAX group, supported by major industry figures such as IBM and Google, suggests that one will become available soon.


            AJAX applications can benefit both the user and the developer. Web applications can respond much more quickly to many types of user interaction and avoid repeatedly sending unchanged information across the network. Also, because AJAX technologies are open, they are supported in all JavaScript-enabled browsers, regardless of operating system – however, implementation differences of the XMLHttpRequest between browsers cause some issues, some using an ActiveX object, others providing a native implementation. The upcoming W3C 'Document Object Model (DOM) Level 3 Load and Save Specification' provides a standardised solution, but the current solution has become a de facto standard and is therefore likely to be supported in future browsers. 


            Although the techniques within AJAX are relatively mature, the overall approach is still fairly new and there has been criticism of the usability of its applications. One of the major causes for concern is that JavaScript needs to be enabled in the browser for AJAX applications to work. This setting is out of the developer's control and statistics show that currently 10% of browsers have JavaScript turned off . This is often for accessibility reasons or to avoid scripted viruses.