XMLHttpRequest.status

XMLHttpRequest.status 屬性根據XMLHttpRequest的回應傳回數值化的狀況編碼。狀況編碼為一正短整數（unsigned short）。Before the request is complete, the value of status will be 0. It is worth noting that browsers report a status of 0 in case of XMLHttpRequest errors too.

The status codes returned are the standard HTTP status codes. For example, status 200 denotes a successful request. If the server response doesn't explicitly specify a status code, XMLHttpRequest.status will assume the default value of 200.

var xhr = new XMLHttpRequest();
console.log('UNSENT', xhr.status);

xhr.open('GET', '/server', true);
console.log('OPENED', xhr.status);

xhr.onprogress = function () {
  console.log('LOADING', xhr.status);
};

xhr.onload = function () {
  console.log('DONE', xhr.status);
};

xhr.send(null);

/**
 * Outputs the following:
 *
 * UNSENT 0
 * OPENED 0
 * LOADING 200
 * DONE 200
 */

[1] Internet Explorer versions 5 and 6 lacked the XMLHttpRequest object, but provided a way to make AJAX requests using ActiveXObject.

• List of HTTP response codes