So, let??™s look at each component technology
in turn.
Asynchronous
In order for an Ajax application to be an Ajax application, it needs to talk with the server without a page
refresh. This is known as asynchronous data exchange and is generally performed using the web browser??™s
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XMLHttpRequest object. A hidden iframe element can also be used. The XMLHttpRequest object is
essentially a mini web browser built into the web browser that can be used by JavaScript without interrupting
the user. Thus it is ideal for Ajax applications.
JavaScript
The key component in Ajax technologies is JavaScript and the browser??™s Document Object Model (DOM) to
allow for manipulation of the webpage using scripts. JavaScript is a full blown programming language in its
own right and has been implemented in mainstream browsers since 1995. The DOM is a standardized way of
representing the elements of a web page as a tree of objects that can be manipulated by JavaScript. Within
Ajax applications, this is the means by which the application dynamically changes the webpage to show new
information without the server??™s sending new data.
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