The keystone of AJAX is the XMLHttpRequest object.
All modern browsers support the XMLHttpRequest object (IE5 and IE6 use an ActiveXObject).
The XMLHttpRequest object is used to exchange data with a server behind the scenes. This means that it is possible to update parts of a web page, without reloading the whole page.
All modern browsers (IE7+, Firefox, Chrome, Safari, and Opera) have a built-in XMLHttpRequest object.
Syntax for creating an XMLHttpRequest object:
Old versions of Internet Explorer (IE5 and IE6) uses an ActiveX Object:
To handle all modern browsers, including IE5 and IE6, check if the browser supports the XMLHttpRequest object. If it does, create an XMLHttpRequest object, if not, create an ActiveXObject:
In the next chapter you will learn about sending server requests.
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