AJAX allows web pages to asynchronously update parts of a page without reloading the entire page. It uses a combination of XMLHttpRequest objects, JavaScript, DOM, and XML to exchange small amounts of data with a server in the background. This improves speed, usability, and interactivity compared to conventional web pages that reload the full page for any new content. Some examples of sites using AJAX are Google Maps, Gmail, YouTube, and Facebook.

1. OVERVIEW OF AJAX

2. KEY POINTS
 AJAX was designed by Jesse James Garrett.
 AJAX became widespread during late 2005.
 It is a Client Side Web Development Technique.
 Used to develop Asynchronous web application.
ASYNCHRONOUS JAVASCRIPT AND XML
(AJAX)

3. WHAT IS AJAX?
 Ajax is a client side technology, that can help increase the speed and usability of an
application's web pages by updating only part of the page at a time, rather than
requiring the entire page to be reloaded after a user-initiated change.
 Using Ajax, the pages of your application can exchange small amounts of data with
the server without going through a form submit.
 AJAX is a technique for creating fast and dynamic web pages.
 AJAX allows web pages to be updated asynchronously by exchanging small amounts
of data with the server behind the scenes. This means that it is possible to update
parts of a web page, without reloading the whole page.

4. AJAX is based on internet standards, and uses a combination of:
 XMLHttpRequest object (to exchange data asynchronously
with a server)
 JavaScript/DOM (to display/interact with the information)
 CSS (to style the data)
 XML (often used as the format for transferring data)
THE AJAX TECHNIQUE

6.  JavaScript allows for interaction with the browser and responding to
events.
 DOM for accessing and manipulating the structure of the HTML of the
page.
 XML which represents the data passed between the server and client.
 An XMLHttpRequest object for asynchronously exchanging the XML
data between the client and the server.
 Classic web pages, (which do not use AJAX) must reload the entire page if the
content should change.

7. PROBLEMS WITH CONVENTIONAL WEB
APPLICATIONS

8.  Interruption of user operation
 Users cannot perform any operation while waiting for a response
 Loss of operational context during refresh
 Loss of information on the screen
 Loss of scrolled position
 No instant feedback's to user activities
 A user has to wait for the next page
 Constrained by HTML
 Lack of useful widgets
 These are the reasons why Rich Internet Application (RIA) technologies
were born.

9.  With an HTTP request, a web page can make a request to, and get a
response from a web server - without reloading the page.
 The user will stay on the same page, and he or she will not notice that
scripts request pages, or send data to a server in the background.
 HTML and HTTP are weak.
 “Click, wait, and refresh” user interaction
 Synchronous “request/response” communication model
ADVANTAGES OF USING AJAX

10. EXAMPLES
Several applications using AJAX includes the following:
 Google Map
 Gmail
 YouTube
 Facebook