What is AJAX?
AJAX enables developers to create web pages which provide a much richer user experience
by providing real-time communication with the hosting server without causing the entire HTML document to
be reloaded.
AJAX is defined in wikipedia as follows:
Ajax, shorthand for Asynchronous JavaScript and XML, is a web development technique
for creating interactive web applications. The intent is to make web pages feel more
responsive by exchanging small amounts of data with the server behind the scenes, so
that the entire web page does not have to be reloaded each time the user makes a change.
This is meant to increase the web page's interactivity, speed, and usability.
Examples of AJAX can be found in applications such as Google Mail, Google Maps,
Live.Com, Facebook.com, and AOL Webmail.
The popularity of AJAX has been growing immensely since the Google Mail application was
released. Despite the newly found popularity of AJAX, people have been using
AJAX since a long time before Google Mail was around, and before the
term AJAX came into existence.
AJAX brings together the features of javascript, CSS, and the XMLHttpRequest
object to create a sense of realtime responsive-ness from your web application.
These tehcnologies make up the core of client side web development when also combined
with HTML. Javascript can be used to manipulate the visual objects on the
page. HTML and CSS are used to define the initial structure and layout of
your page. The XMLHttpRequest object has been around for quite a while but is
just getting alot of publicity now. The XMLHttpRequest object started out as
an activex control that was installed on a users pc with the Windows operating system.
This activex object was originally party of the Microsoft XML library.
The XMLHttpRequest has currently been standardized and is provided as a built in capability
of web browser applications such as FireFox and IE 7.
For example, in Internet Explorer 6.1 or older you would use javascript similar to the following
to create an instance of an XmlHttp object:
var xmlHttpReq = new ActiveXObject("Microsoft.XMLHTTP");
while in FireFox, Safari, Opera, Netscape, and Mozilla you would do the following:
var xmlHttpReq = new XMLHttpRequest()
IE 7 supports a native XMLHttpRequest object that
is more efficient than the outdated idea of creating an ActiveX object to do the same thing.
However you will still need to support using the ActiveX version in your code, since not everyone
will be running IE 7 right away.
Information about the HttpRequest changes in Internet Explorer 7
To continue learning go to "AJAX for Beginners" -->