XMLHttpRequest.readyState - Web APIs 编辑

The XMLHttpRequest.readyState property returns the state an XMLHttpRequest client is in. An XHR client exists in one of the following states:

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 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

Browser compatibility

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