--- title: XMLHttpRequest.onreadystatechange slug: Web/API/XMLHttpRequest/readystatechange_event translation_of: Web/API/XMLHttpRequest/onreadystatechange original_slug: Web/API/XMLHttpRequest/onreadystatechange ---
{{APIRef}}

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 {{event("readystatechange")}} event is fired, that is every time the {{domxref("XMLHttpRequest.readyState", "readyState")}} property of the {{domxref("XMLHttpRequest")}} changes.

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

The readystatechange event will not be fired when an XMLHttpRequest request is cancelled with the abort() method.

UPDATE: it's firing in the latest version of browsers (Firefox 51.0.1, Opera 43.0.2442.991, Safari 10.0.3 (12602.4.8), Chrome 54.0.2840.71, Edge, IE11). Example here - just reaload page few times.

語法

XMLHttpRequest.onreadystatechange = callback;

範例

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

xhr.open(method, url, true);
xhr.onreadystatechange = function () {
        if(xhr.readyState === XMLHttpRequest.DONE && xhr.status === 200) {
            console.log(xhr.responseText);
        }
    };
xhr.send();

規範

Specification Status Comment
{{SpecName('XMLHttpRequest', '#handler-xhr-onreadystatechange')}} {{Spec2('XMLHttpRequest')}} WHATWG living standard

瀏覽器相容性

{{Compat("api.XMLHttpRequest.readystatechange_event")}}