Ajax, or AJAX, is a web development technique used for creating interactive web applications. The intent is to make web pages feel more responsive by exchanging small amounts of data with the server behind the scenes, so that the entire web page does not have to be reloaded each time the user requests a change. This is intended to increase the web page’s interactivity, speed, functionality, and usability.
The name is shorthand for Asynchronous JavaScript and XML. Ajax is asynchronous in that loading does not interfere with normal page loading. JavaScript is the programming language in which Ajax function calls are made. Data retrieved using the technique is commonly formatted using XML, as reflected in the naming of the XMLHttpRequest object from which Ajax is derived.
Ajax is a cross-platform technique usable on many different operating systems, computer architectures, and Web browsers as it is based on open standards such as JavaScript and XML, together with open source implementations of other required technologies.
Constituent technologies
Ajax uses a combination of:
- XHTML (or HTML) and CSS, for marking up and styling information.
- The DOM accessed with a client-side scripting language, especially ECMAScript implementations such as JavaScript and JScript, to dynamically display and interact with the information presented.
- The XMLHttpRequest object is used to exchange data asynchronously with the web server. In some Ajax frameworks and in certain situations, an IFrame object is used instead of the XMLHttpRequest object to exchange data with the web server, and in other implementations, dynamically added
<script>tags may be used. - XML is sometimes used as the format for transferring data between the server and client, although any format will work, including preformatted HTML, plain text and JSON. These files may be created dynamically by some form of server-side scripting.
Like DHTML, LAMP, and SPA, Ajax is not a technology in itself, but a term that refers to the use of a group of technologies.
The “core” and defining element of Ajax is the XMLHttpRequest object, which gives browsers the ability to make dynamic and asynchronous data requests without having to unload and reload a page. Given XMLHttpRequest can eliminate the need for page refreshes, other technologies have become more prominently used and highlighted with this development approach.
Besides XMLHttpRequest, the use of DOM, CSS, and JavaScript provides a more-enhanced “single-page” experience.
History
The first use of the term in public was by Jesse James Garrett in February 2005. Garrett thought of the term when he realized the need for a shorthand term to represent the suite of technologies he was proposing to a client.
Although the term Ajax was coined in 2005, most of the technologies that enable Ajax started a decade earlier with Microsoft’s initiatives in developing Remote Scripting. Referring to the idea as Inner-Browsing, Netscape Evangelism published an article in 2003 which presented ideas for implementing models in which “all navigation occurs within a single page, as in a typical application interface.”[2] Techniques for the asynchronous loading of content on an existing Web page without requiring a full reload date back as far as the IFRAME element type (introduced in Internet Explorer 3 in 1996) and the LAYER element type (introduced in Netscape 4 in 1997, abandoned during early development of Mozilla). Both element types had a src attribute that could take any external URL, and by loading a page containing JavaScript that manipulated the parent page, Ajax-like effects could be attained. This set of client-side technologies was usually grouped together under the generic term of DHTML. Macromedia’s Flash could also, from version 4, load XML and CSV files from a remote server without requiring a browser to be refreshed.
Microsoft’s Remote Scripting (MSRS), introduced in 1998, acted as a more elegant replacement for these techniques, with data being pulled in by a Java applet with which the client side could communicate using JavaScript. This technique worked on both Internet Explorer version 4 and Netscape Navigator version 4 onwards. Microsoft then created the XMLHttpRequest object in Internet Explorer version 5 and first took advantage of these techniques using XMLHttpRequest in Outlook Web Access supplied with the Microsoft Exchange Server 2000 release.
The Web development community, first collaborating via the microsoft.public.scripting.remote newsgroup and later through blog aggregation, subsequently developed a range of techniques for remote scripting to enable consistent results across different browsers. In 2002, a user-community modification to Microsoft Remote Scripting was made to replace the Java applet with XMLHttpRequest.
Remote Scripting Frameworks such as ARSCIF surfaced in 2003 not long before Microsoft introduced Callbacks in ASP.NET.
In addition, the World Wide Web Consortium has several Recommendations that also allow for dynamic communication between a server and user agent, though few of them are well supported. These would include:
- The object element defined in HTML 4 for embedding arbitrary content types into documents, (replaces inline frames under XHTML 1.1)
- The Document Object Model (DOM) Level 3 Load and Save Specification
Accessibility
Non-Ajax users would ideally continue to load and manipulate the whole page as a fallback, enabling the developers to preserve the experience of users in non-Ajax environments (including all relevant accessibility concerns) while giving those with capable browsers a much more responsive experience.
Licensed under the GNU Free Documentation License. It uses materials from the Wikipedia.
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