gistfile1.js

function getImage (url) {
  var res;
  var xhr = new XMLHttpRequest();
  xhr.open('GET', url, false);
  xhr.responseType = 'arraybuffer';
  xhr.onload = function () {
    res = btoa(String.fromCharCode.apply(null, new Uint8Array(xhr.response)))
  };
  xhr.send();
  return res;
}