After an XMLHttpRequest (XHR) object has been created, the open method has been called on a URL against the XHR object and the URL has been sent to a web server, the next step is to listen for a response. This is done via the onreadystatechange property of the XMLHttpRequest object, as follows:
objXHR.onreadystatechange = function(evt){
if (objXHR.readyState == 4) {
if(objXHR.status == 200)
//Handle processing here
else
document.write('Error processing request');
}
};
objXHR.send(null);
Possible readyState values are:
0 = open has not yet been called
1 = send has not yet been called but open has been called
2 = send has been called but no response from server
3 = data is in the process of being received from the server
4 = response from server has arrived
