The readyState is XMLHttpRequest property that describes the current state of XMLHttpRequest object.
State value Explanation State of XMLHttpRequest object
readyState = 0 Request not initialized XMLHttpRequest object is created but open() method not called
readyState = 1 Request is set Open() method has been called, but before send() method is called
readyState = 2 Request is sent After send() method is called
readyState = 3 Request is under process Browser has connection established with Server, but Server has not yet completed with Response
readyState = 4 Request is complete Request is completed, response data received at browser from the Server
