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Ajax (Asynchronous Javascript & XML) is a group of interelated web development techniques used o the client side to create interactive web applications or rich internet applications. With AJAX, web applications can retreive data from the server asyncronously in the background without interfeing with the display and behaviour of the existing page. 

The use of AJAX tecnology has led to

  • An increase in interactive or dynamic interfaces on webpages.
  • Better quality of web services due to asynchronous mode.
  • Using AJAX, a web application can request only the content that needs to be updated, thus drastically reducing bandwidth usage and load time.
  • It allows to respond quickly to inputs, and sections of pages can also be reloaded individually. Users may perceive the application to be faster or more responsive, even if the application has not changed on the server side.

Technologies included in AJAX:
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 Garett explained that the following technologies are required:

  • XTML & CSS for presentation
  • The Document Object model for dynamic display of and interaction with data.
  • XML & XSLT for the interchange, and manipulation and display of data respectively
  • The XMLHttpRequest object for asynchronous.
  • Javascript to bring these technologies together


  • AJAX interfaces are harder to develop properly.
  • Pages dynamically created using successive AJAX requests do not automatically register themselves with the browser's history engine, so clicking the browser's "back" button may not return the user to an earlier state of the AJAX-enabled page.
  • Dynamic webpage updates also make it difficult for a user to bookmark a particular state of application
  • Any user whose browser does not support JavaScript or XMLHttpRequest, or simply has this functionality disabled, will not be able to properly use pages which depend on AJAX.
  • Devices such as mobile phones, PDAs and screen readers may not have support for the required technologies
  • AJAX-powered interfaces may dramatically increase the number of user-generated requests to web servers and their back-ends (databases, or other). This can lead to longer response times and/or additional hardware needs.
  • User interfaces can be confusing or behave inconsistently when normal web patterns are not followed