Ajax
is a group of interrelated web development techniques used on the client-side to create asynchronous web applications. With Ajax, web applications can send data to, and retrieve data from, a server
asynchronously (in the background) without interfering with the display
and behavior of the existing page. Data can be retrieved using the
XMLHttpRequest object. Despite the name, the use of XML is not required (JSON is often used instead), and the requests do not need to be asynchronous.
Ajax is not a single technology, but a group of technologies. HTML and CSS can be used in combination to mark up and style information. The DOM
is accessed with JavaScript to dynamically display, and allow the user
to interact with, the information presented. JavaScript and the
XMLHttpRequest object provide a method for exchanging data
asynchronously between browser and server to avoid full page reloads.
History
In the 1990s, most web sites were based on complete HTML pages. Each
user action required that the page be reloaded from the server (or a new
page loaded). This process was inefficient, as reflected by the user
experience: all page content disappeared then reappeared. Each time a
page was reloaded due to a partial change, all of the content had to be
re-sent, even though only some of the information had changed. This
placed additional load on the server and used excessive bandwidth. In 1996, the iframe tag was introduced by Internet Explorer to load content asynchronously.
In 1998, Microsoft Outlook Web Access team implemented the first component XMLHTTP by client script.
In 1999, Microsoft utilized its iframe technology to dynamically
update the news stories and stock quotes on the default page for
Internet Explorer, and created the XMLHTTP ActiveX control in Internet Explorer 5, which was later adopted by Mozilla, Safari, Opera and other browsers as the XMLHttpRequest JavaScript object. Microsoft has adopted the native XMLHttpRequest model as of Internet Explorer 7, though the ActiveX version is still supported. The utility of background HTTP
requests to the server and asynchronous web technologies remained
fairly obscure until it started appearing in full scale online
applications such as Outlook Web Access (2000) and Oddpost (2002).
Google made a wide deployment of standards-compliant, cross browser Ajax with Gmail (2004) and Google Maps (2005).
The term Ajax was coined on 18 February 2005 by Jesse James Garrett in an article entitled "Ajax: A New Approach to Web Applications", based on techniques used on Google pages.
On 5 April 2006, the World Wide Web Consortium (W3C) released the first draft specification for the XMLHttpRequest object in an attempt to create an official web standard.
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