Step by Step to AJAX - XmlHttpRequest

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One of the key objects needed for working with AJAX is the XMLHttpRequest Object. This object does two things: it handles the httpRequest, and then it processes the XML response. This was implemented in Internet Explorer 5 for Windows as an ActiveX Object. This has been implemented by Mozilla 1.0, Apple and others in compatible forms. The W3C has similar standards for the DOM Level 3 specification. We will take a brief look at this object before we put it to work. Some of the highlighted methods and properties are later used while fetching a web page to show what values they do return.

Creating the XML HttpRequest object

This is the easy part, if you need to deal only with Microsoft IE. For Mozilla you would instantiate the object using the following syntax:

var xhr=new XMLHttpRequest();

where as for IE you would use the following:

var xhr=new ActiveXObject("Microsoft.XMLHTTP");

Both of these methods create an object which is hidden from the user. Its methods and properties take control of the server interaction. For cross browser applications you need to come up with a branching syntax. This is not so difficult; see for example the cross-browser boiler plate code (Listing 2.0 in the link)

Next: XMLHttpRequest Object Methods >>
 

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