onreadystatechange

Defines a function to be called when the readyState property changes

readyState

0: request not initialized.
1: OPENED open() has been called. Server connection established.
2: HEADERS_RECEIVED request received. send() has been called, and headers and status are available.
3: LOADING processing request. Downloading; responseText holds partial data.
4: DONE request finished and response is ready.

status

200: "OK"
403: "Forbidden"
404: "Page not found"

statusText
Returns the status-text (e.g. "OK" or "Not Found")