AJAX stands for Asynchronous
JavaScript and XML. It is a cornerstone of Web 2.0
applications. In addition to JavaScript and XML, Ajax uses HTML / XHTML / dynamic HTML,
Cascading Style Sheets (CSS), and and XSLT.
Ajax is a client side technology, and uses JavaScript and the
XMLHttpRequest object
to communicate with the server behind the scenes.
Typically, this happens by including JavaScript code inside the HTML code for the
web page. The JavaScript code fetches data from the server either in
text or XML format. This data is downloaded into an XMLHttpRequest object supported by
the browser. This object handles the download behind the scenes, and stores the
downloaded data. Then, JavaScript retrieves that data from the XMLHttpRequest object
and displays the data as required by the Web application.
Google gmail is a good example of a Web 2.0 Ajax application. Suppose you want to attach
a file to your email. In gmail, while the file is being attached, you can continue finishing your
email, because the file attachment is happening behind the scenes. Compare this with
other email applications like Yahoo! or Hotmail, where you have to stop typing out your
email when you attach a file (the application goes into a wait mode while the file is being
attached in Yahoo! or Hotmail). Thus, AJAX based gmail is clearly a superior email
application compared to Yahoo! mail or Hotmail.
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