Why do we use the XMLHttpRequest object in AJAX?
The XMLHttpRequest object is used by JavaScript to transfer XML and other text data among client and server. The XMLHttpRequest object permits a client-side script to perform an HTTP request. AJAX applications use the XMLHttpRequest object so that the browser can link to the server without requiring a postback of the entire page. In previous versions of Internet Explorer, MSXML ActiveX component is liable to give this functionality; while, Internet Explorer 7 and other browsers, like Mozilla Firefox, XMLHttpRequest is not liable to.