XMLHttpRequest: readyState property

Note: This feature is available in Web Workers, except for Service Workers.

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, all redirects (if any) have been followed 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.

Example

const 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 = () => {
  console.log("LOADING", xhr.readyState); // readyState will be 3
};

xhr.onload = () => {
  console.log("DONE", xhr.readyState); // readyState will be 4
};

xhr.send(null);

Specifications

Specification
XMLHttpRequest Standard # states

Browser compatibility

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