[1] The methods allow a browser-based application to send requests to the server after page loading is complete, and receive information back.
Prior to Ajax, hyperlinks and form submissions were the primary mechanisms for interacting with the server, often replacing the current page with another one.
[4] The XMLHttpRequest identifier is now the de facto standard in all the major browsers, including Mozilla's Gecko layout engine (2002),[5] Safari 1.2 (2004) and Opera 8.0 (2005).
[6] The World Wide Web Consortium (W3C) published a Working Draft specification for the XMLHttpRequest object on April 5, 2006.
[8] Level 2 added methods to monitor event progress, allow cross-site requests, and handle byte streams.
[13] The response can be parsed from the JSON format into a readily usable JavaScript object, or processed gradually as it arrives rather than waiting for the entire text.
XMLHttpRequest data is subject to this security policy, but sometimes web developers want to intentionally circumvent its restrictions.