An EventHandler that is called whenever the readyState attribute changes. The callback is called from the user interface thread. The XMLHttpRequest.onreadystatechange property contains the event handler to be called when the readystatechange event is fired, that is every time the readyState property of the XMLHttpRequest changes.

Warning: This should not be used with synchronous requests and must not be used from native code.


XMLHttpRequest.onreadystatechange = callback;


  • callback is the function to be executed when the readyState changes.


const xhr = new XMLHttpRequest(),
    method = "GET",
    url = "https://developer.mozilla.org/";

xhr.open(method, url, true);
xhr.onreadystatechange = function () {
  // In local files, status is 0 upon success in Mozilla Firefox
  if(xhr.readyState === XMLHttpRequest.DONE) {
    var status = xhr.status;
    if (status === 0 || (status >= 200 && status < 400)) {
      // The request has been completed successfully
    } else {
      // Oh no! There has been an error with the request!


Specification Status Comment
XMLHttpRequest Living Standard WHATWG living standard

Browser compatibility

ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung Internet
onreadystatechangeChrome Full support 1Edge Full support 12Firefox Full support 1IE Full support 5Opera Full support 9Safari Full support 1.2WebView Android Full support 1Chrome Android Full support 18Firefox Android Full support 4Opera Android Full support 10.1Safari iOS Full support 1Samsung Internet Android Full support 1.0


Full support
Full support