The XMLHttpRequest.readyState property returns the state an XMLHttpRequest client is in. An XHR client exists in one of the following states:
Value
State
Description
0
UNSENT
Client has been created. open() not called yet.
1
OPENED
open() has been called.
2
HEADERS_RECEIVED
send() has been called, and headers and status are available.
3
LOADING
Downloading; responseText holds partial data.
4
DONE
The operation is complete.
UNSENT
The XMLHttpRequest client has been created, but the open() method hasn't been called yet.
OPENED
open() method has been invoked. During this state, the request headers can be set using the setRequestHeader() method and the send() method can be called which will initiate the fetch.
HEADERS_RECEIVED
send() has been called and the response headers have been received.
LOADING
Response's body is being received. If responseType is "text" or empty string, responseText will have the partial text response as it loads.
DONE
The fetch operation is complete. This could mean that either the data transfer has been completed successfully or failed.
The state names are different in Internet Explorer. Instead of UNSENT, OPENED, HEADERS_RECEIVED, LOADING and DONE, the names READYSTATE_UNINITIALIZED (0), READYSTATE_LOADING (1), READYSTATE_LOADED (2), READYSTATE_INTERACTIVE (3) and READYSTATE_COMPLETE (4) are used.
Example
var xhr = new XMLHttpRequest();
console.log('UNSENT', xhr.readyState); // readyState will be 0
xhr.open('GET', '/api', true);
console.log('OPENED', xhr.readyState); // readyState will be 1
xhr.onprogress = function () {
console.log('LOADING', xhr.readyState); // readyState will be 3
};
xhr.onload = function () {
console.log('DONE', xhr.readyState); // readyState will be 4
};
xhr.send(null);