JavaScript: The Definitive Guide, 5th Edition

Name

XMLHttpRequest: An HTTP request and response — Firefox 1.0, Internet Explorer 5.0, Safari 1.2, Opera 7.60: Object → XMLHttpRequest

Constructor

new XMLHttpRequest( )                     // All browsers except IE 5 and IE 6
new ActiveXObject("Msxml2.XMLHTTP")      // IE
new ActiveXObject("Microsoft.XMLHTTP")   // IE with older system libraries

Properties

readonly short readyState

The state of the HTTP request. The value of this property begins at 0 when an XMLHttpRequest is first created and increases to 4 when the complete HTTP response has been received. Each of the five states has an informal name associated with it, and the table below lists the states, their names, and their meanings:

State	Name	Description
0	Uninitialized	This is the initial state. The XMLHttpRequest object has just been created or has been reset with the abort( ) method.
1	Open	The open( ) method has been called, but send( ) has not. The request has not yet been sent.
2	Sent	The send( ) method has been called, and the HTTP request has been transmitted to the web server. No response has been received yet.
3	Receiving	All response headers have been received. The response body is being received but is not complete.
4	Loaded	The HTTP response has been fully received.

The value of readyState never decreases, unless abort( ) or open( ) are called on a request that is already in progress. Every time the value of this property increases, the onreadystatechange event handler is triggered.

readonly String responseText ...