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XMLHttp Request object for Ajax

The first step that we have to learn in AJAX is the XMLHTTP request. This we will be using in every Ajax code we write. A good understanding of this will help us in analyzing and developing complex codes.

An agent or a broker

This XMLHttp object is an agent between our application at client side and our programming code at server end. It sends data and collects the return data from the server.

Now we understood that creation of this XMLHttp request is an issue with the browser of the user ( or client ). So the user browser must able to create this XMLHttp object. Unfortunately the old browsers doest not support this and can't create XMLHttp object. So we have to find out first this object is created or not. If the browser fails to create the object then we must give error message saying about the browser issue.

Even if the browser are capable of creating our XMLHttp request they differ in the way they create it. FireFox create the object in a different way than Internet Explorer ( IE ). So based on this we will develop the code and note that we can use this same set of code ( to create the XMLHttp object ) in all pages where we will be using Ajax. Let us develop the code.

We will try with first trying with a simple request like this

if (typeof XMLHttpRequest != "undefined")

The above line will return true for Firfox and Safari so we can create an object. For IE we will use ActiveXObject to create the object. Depending on the type of ActiveXObject support which depends on version of IE we will create the object. If in all fail in crating the object then we will return error message.

Now let us write the function to initialize the HMLHttp Request object

function developXMLHttp() {
if (typeof XMLHttpRequest != "undefined") {
return new XMLHttpRequest();
} else if (window.ActiveXObject) {
var aVersions = [ "MSXML2.XMLHttp.5.0",
"MSXML2.XMLHttp.4.0","MSXML2.XMLHttp.3.0",
"MSXML2.XMLHttp","Microsoft.XMLHttp"
];
for (var x = 0; x < aVersions.length; x++) {
try {
var p2XmlHttp = new ActiveXObject(aVersions[x]);
return p2XmlHttp;
} catch (oError) {
//Do nothing
}
}
}
throw new Error("Error..XMLHttp object could be created.");
}

//To use this function we will create an object like this.

function my_form(){
var myxml=developXMLHttp();
document.write(typeof(myxml));
}
window.onload=my_form();

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