Javascript advanced Article 3 Ajax, JSON, Prototype

I have heard a lot about Ajax, but I have never really touched it, so I 'd like to know a little about it here. The innovation of Ajax technology is that it improves the traditional request-wait-response-refresh-return data mode, and allows users to continue their operations before returning information, the current page will not be... syntaxHighlighter. all ();

Ajax
I have heard a lot about this word, but I have never really touched it, so I 'd like to know it here.
The innovation of Ajax technology is that it improves the traditional "request-wait-response-refresh-return data" mode. Before returning information, users can continue their operations, the current page will not be refreshed due to requests. This greatly improves interactivity.
Ajax is actually not a technology, but composed of many technologies. One of the biggest features is that it can be asynchronously transmitted to implement multi-threaded services.
Ajax asynchronous transmission relies on the XMLHttpRequst object in js, so we start with it.
XMLHttpRequest is an abstract object created by XMLHttp for data interaction. In IE, XMLHttpRequest is used as an ActiveX control and as a built-in js object in FF Opera.
Code for creating an XMLHttpRequest object: