How does it works:-

Ajax uses a programming model with display and events. These events are user actions, they call functions associated to elements of the web page.Interactivity is achieved with forms and buttons. DOM allows to link elements of the page with actions and also to extract data from Xml files provided by the server.

To get data on the server, XMLHttpRequest provides two methods:- open: create a connection.- send: send a request to the server.Data furnished by the server will be found in the attributs of the XMLHttpRequest object:- responseXml for a Xml file or- responseText for a simple text.Take note that a new XMLHttpRequest object has to be created for each new file to load.

We have to wait for the data to be available to process it, and in this purpose, the state of availability of data is given by the readyState attribute of XMLHttpRequest.

States of readyState follow (only the last one is really useful): not initialized.

1: connection etablished.
2: request received.
3: answer in process.
4: finished.