AJAX (Asynchronous JavaScript and XML) is a group of interrelated web development techniques used on the client-side to create interactive web applications. With Ajax, web applications can retrieve data from the server asynchronously in the background without interfering with the display and behavior of the existing page. The use of Ajax techniques has led to an increase in interactive or dynamic interfaces on web pages. Data is usually retrieved using the XMLHttpRequest object. Despite the name, the use of XML is not actually required, nor do the requests need to be asynchronous.


The term Ajax has come to represent a broad group of web technologies that can be used to implement a web application that communicates with a server in the background, without interfering with the current state of the page. In the article that coined the term Ajax, Jesse James Garrett explained that the following technologies are required:

  • HTML or XHTML and CSS for presentation.
  • The Document Object Model for dynamic display of and interaction with data.
  • XML for the interchange of data, and XSLT for its manipulation.
  • The XMLHttpRequest object for asynchronous communication.
  • JavaScript to bring these technologies together

Since then, however, there have been a number of developments in the technologies used in an Ajax application, and the definition of the term Ajax. In particular, it has been noted that:

  • JavaScript is not the only client-side scripting language that can be used for implementing an Ajax application. Other languages such as VBScript are also capable of the required functionality. However, JavaScript is the most popular language for Ajax programming due to its inclusion in and compatibility with the majority of modern web browsers.
  • XML is not required for data interchange and therefore XSLT is not required for the manipulation of data. JavaScript Object Notation (JSON) is often used as an alternative format for data interchange, although other formats such as preformatted HTML or plain text can also be used.

Classic Ajax involves writing ad hoc JavaScript on the client. A simpler if cruder alternative is to use standard JavaScript libraries that can partially update a page, such as ASP. Net’s Update Panel. Tools such as Echo2 and ZK enable fine-grained control of a page from the server, using only standard JavaScript libraries.

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