The onreadystatechang is an property of XMLHttpRequest object.The onreadystatechange event is triggered every time the readyState changes. It stores a function (or the name of a function) to be called automatically each time the readyState property changes

Ajaxgold framework is a framework which leverages Ajax, a collection of technologies for building dynamic web pages on the client side. While data is read from and sent to the server by JavaScript requests, frameworks may include server-side or client-side components to process the client's requests.

LibAjax is a library that allows the use of server side and client side scripting using XMLHTTPRequest (Named AJAX). LibAjax makes using Ajax even easier.
The libAjax function are :
1.$ajax->output()
2.$ajax->client_request()

The getResponseHeader method is used to get only data for a specific header, the “Last-Modified” header, like this:
XMLHttpRequestObject.getResponseHeader(“Last-Modified”)

The Http framework supports forced caching in Firefox as well as forced non-caching in Internet Explorer. Internet Explorer caches the response from the server by default, so clicking the top Get Time button always gives us the same time. But the Http package can avoid caching (which it does by appending unique data to the end of an URL each time we call the URL). For example, when we click the second button from the top in the figure, the time is updated for each button click, even in Internet Explorer.