Ajax and Asynchronous Interface

AJAX

Ajax (also AJAX; short for asynchronous JavaScript and XML)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 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 in the AJAJ variant), and the requests do not need to be asynchronous.

Ajax is not a 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.

AJAX can be used to 

1. Update a web page without reloading the page
2. Request data from a server - after the page has loaded
3. Receive data from a server - after the page has loaded
4. Send data to a server - in the background 

How AJAX Works

Fig 1. Working Of AJAX

Asynchronous Interface 

If you use XMLHttpRequest from an extension, you should use it asynchronously.  In this case, you receive a callback when the data has been received, which lets the browser continue to work as normal while your request is being handled.