Retrieves the current state of the request operation.
The object has been created, but not initialized (the open method has not been called).
A request has been opened, but the send method has not been called.
The send method has been called. No data is available yet.
Some data has been received; however, responseText is not available.
All the data has been received.
- XMLHttpRequest, Section 3.5
You cannot call the responseText property to obtain partial results (readyState = 3). Doing so will return an error, because the response is not fully received. You must wait until all data has been received.
In comparison, the Microsoft XML (MSXML) version of the IXMLHTTPRequest interface exposes partial results through the responseStream property. Be aware that this behavior also differs from the IServerXMLHTTPRequest interface, which provides partial results to responseText.
For an example of how to use this property, see onreadystatechange.