Google's Gmail
and Outlook Express are two familiar examples that use Ajax techniques.
Ajax has various applications, some of which are discussed below.
1. Dynamic Form Data Validation. As an example, suppose a user fills
out a form to register with a web site.The validity of data in the form
is not checked till the form is submitted. With Ajax, the data added to
the form is dynamically validated using business logic in a server
application. Thus, a complete form does not have to be posted to the
server to check if data in the form is valid.
2. Auto completion. As a user adds some data to a form, the remaining
form gets auto completed.
3. Refreshing data on a page. Some web pages require that data be
refreshed frequently, a weather web site for example. Using the Ajax
technique, a web page may poll the server for latest data and refresh
the web page without reloading the page.
Ajax is based on XMLHttpRequest, JavaScript and XML DOM
technologies. JavaScript and XML DOM technologies are relatively old
technologies. Therefore we won??™t discuss these. XMLHttpRequest is a
2 1 What is Ajax?
relatively new technology. In the next section, we shall discuss the
XMLHttpRequest technology.
1.2 What is XMLHttpRequest?
Ajax takes advantage of an object built into all modern browsers-the
XMLHttpRequest object-to send and receive HTTP requests and
responses. An HTTP request sent via the XMLHttpRequest object does
not require the page to have or post a