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11.2. XMLHTTP and XMLHttpRequest

Even the methods now referred to as "AJAX" are not new. Microsoft's version of the interface, XMLHTTP, has been available as an ActiveX object in various incarnations since a preview release of IE 5.0 in late 1998 (the final release of IE 5.0 was in March 1999). Companies have been capitalizing on this development model in IE-only environments for years. Beginning slightly before the release of version 1.0 of Mozilla's browser product, a native object, modeled after Microsoft's interface and named XMLHttpRequest, has been available. Recently, Safari (since version 1.2), Opera (since version 8), and Konqueror have included compliant interfaces, also named XMLHttpRequest.

In the last few months, the use of XMLHTTP and its variants has increased dramatically. The adoption of the technology by Google in their Google Suggest and Google GMail product offerings has been primarily responsible for introducing the development method to the masses. Additionally, an article by Adaptive Path coining the term "AJAX" allowed developers to refer to the collection of technologies with one unifying name, which has facilitated communication and awareness of the subject.

11.2.1. The Interfaces

The following are the methods of the XMLHTTP and XMLHttpRequest interfaces that are relevant and, for the most part, supported in all browsers:

• abort(): Aborts a request.

• getResponseHeader(key): Returns the value of the HTTP response header named key.

• open(method, uri, [async, ...