The XMLHttpRequestEventTarget.onload is the function called when an XMLHttpRequest transaction completes successfully. 
XMLHttpRequest.onload = callback;
callback is the function to be executed when the request completes successfully. It receives a ProgressEvent object as its first argument. The value of this (i.e. the context) is the same XMLHttpRequest this callback is related to. var xmlhttp = new XMLHttpRequest(), method = 'GET', url = 'https://developer.mozilla.org/'; xmlhttp.open(method, url, true); xmlhttp.onload = function () { // Do something with the retrieved data ( found in xmlhttp.response ) }; xmlhttp.send();
| Desktop | Mobile | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Chrome | Edge | Firefox | Internet Explorer | Opera | Safari | WebView Android | Chrome Android | Firefox for Android | Opera Android | Safari on IOS | Samsung Internet | |
onload | 
1  | 
12  | 
1  | 
10  | 
≤12.1  | 
1.3  | 
≤37  | 
18  | 
4  | 
≤12.1  | 
1  | 
1.0  | 
    © 2005–2021 MDN contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
    https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequestEventTarget/onload