About Native XMLHTTP

Ref. : About Native XMLHTTP

XMLHTTP in IE7 vs. IE6

The native implementation of the XMLHTTP object is designed with cross-browser compatibility in mind. With just a bit of script, it is easy to build a function that works with either version of Internet Explorer, or any browser that supports XMLHTTP. See XMLHttpRequest for complete documentation and examples.

var xmlHttp = null;
if (window.XMLHttpRequest) {
  // If IE7, Mozilla, Safari, and so on: Use native object.
  xmlHttp = new XMLHttpRequest();
}
else
{
  if (window.ActiveXObject) {
     // ...otherwise, use the ActiveX control for IE5.x and IE6.
     xmlHttp = new ActiveXObject('MSXML2.XMLHTTP.3.0');
  }
}