XMLHttpRequest was first introduced by Microsoft in Internet Explorer 5.0 as an ActiveX control. However, in IE7 and other browsers XMLHttpRequest is a native JavaScript object.
In all modern browsers, you can create a new XMLHttpRequest object using the following code:
var request = new XMLHttpRequest()
However, if you need to also support Internet Explorer 6 and older, you need to extend your code like this:
if (window.XMLHttpRequest) {
//Firefox, Opera, IE7, and other browsers will use the native object
var request = new XMLHttpRequest();
} else {
//IE 5 and 6 will use the ActiveX control
var request = new ActiveXObject("Microsoft.XMLHTTP");
}