Internet Explorer on Windows, Safari on Mac OS-X, Mozilla on all platforms, Konqueror in KDE, IceBrowser on Java, and Opera on all platforms including Symbian provide a method for client side javascript to make HTTP requests. From the humble begins as an oddly named object with few admirers, it's blossomed to be the core technology in something called AJAX [1].
The Object makes many things easier and neater than they other would be, and introduces some things that were otherwise impossible such as HEAD requests to see when a resource was last modified, or to see if it even exists. It makes your scripting options more flexible allowing for POST requests without having the page change, and opens up the possibility of using PUT, DELETE etc. These methods are increasingly used to provide richer Web Applications like G-Mail that use lower bandwidth and offer snappier user interaction.
Why XML HTTP Request object?
Whilst the object is called the XML HTTP Request object it is not limited to being used with XML, it can request or send any type of document, although dealing with binary streams can be problematical in javascript.
Creating the object
In Internet Explorer, you create the object using new ActiveXObject("Msxml2.XMLHTTP") or new ActiveXObject("Microsoft.XMLHTTP") depending on the version of MSXML installed. In Mozilla and Safari (and likely in future UA's that support it) you use new XMLHttpRequest() IceBrowser uses yet another method the window.createRequest() method.
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