Sunava Dutta on the Internet Explorer team has written about their support for a Native XMLHTTPRequest object in IE 7. He writes

I’m excited to mention that IE7 will support a scriptable native version of XMLHTTP. This can be instantiated using the same syntax across different browsers and decouples AJAX functionality from an ActiveX enabled environment.

What is XMLHTTP?

XMLHTTP was first introduced to the world as an ActiveX control in Internet Explorer 5.0. Over time, this object has been implemented by other browsing platforms, and is the cornerstone of “AJAX” web applications. The object allows web pages to send and receive XML (or other data) via the HTTP protocol. XMLHTTP makes it possible to create responsive web applications that do not require redownloading the entire page to display new data. Popular examples of AJAX applications include the Beta version of Windows Live Local, Microsoft Outlook Web Access, and Google’s GMail.

Charting the changes: XMLHTTP in IE7 vs. IE6

In IE6 and below, XMLHTTP is implemented as an ActiveX object provided by MSXML.

In IE7, XMLHTTP is now also exposed as a native script object. Users and organizations that choose to disable ActiveX controls can still use XMLHTTP based web applications. (Note that an organization may use Group Policy or IE Options to disable the new native XMLHTTP object if desired.) As part of our continuing security improvements we now allow clients to configure and customize a security policy of their choice and simultaneously retain functionality across key AJAX scenarios.

IE7’s implementation of the XMLHTTP object is consistent with that of other browsers, simplifying the task of cross-browser compatibility.  Using just a bit of script, it’s easy to build a function which works with any browser that supports XMLHTTP:

if (window.XMLHttpRequest){

          // If IE7, Mozilla, Safari, etc: Use native object
          var xmlHttp = new XMLHttpRequest()

}
else
{
if (window.ActiveXObject){

          // ...otherwise, use the ActiveX control for IE5.x and IE6
          var xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
          }

}

Note that IE7 will still support the legacy ActiveX implementation of XMLHTTP alongside the new native object, so pages currently using the ActiveX control will not require rewrites.

I wonder if anyone else sees the irony in Internet Explorer copying features from Firefox which were originally copied from IE?