XMLHttpRequestEventTarget.onload

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();