The readyState property indicates the current state of the request. It returns a 4-byte integer.

This property is read-only and has the following defined values

• UNINITIALIZED(0)
  The object has been created, but has not been initialized (the open method has not been called).
• LOADING(1)
  The object has been created but the send method has not been called.
• LOADED(2)
  The send method has been called and the status and headers are available, but the response is not.
• INTERACTIVE(3)
  some data has been received. You can get the partial results using the responseBody and the responseText properties.
• COMPLETED(4)
  All the data has been received, and is available.

This property is a Microsoft extension to the W3C DOM.