XMLHttpRequest.readyState

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.

Note: The state names are different in versions of Internet Explorer earlier than 11. 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);

Specifications

Specification
XMLHttpRequest Standard # states

Browser compatibility

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