function get(url, callback) {
  var req = new XMLHttpRequest();
  req.open('GET', url, true);

  req.onreadystatechange = function () {
    if (req.readyState === 4) {
      if (req.status === 200) {
        callback(req.response, false);
      } else {
        callback(req, req.statusText);
      }
    }
  };

  req.send();
}
AJAX Get utility function.
@function
@async
@param {string} url - URL of the request.
@param {function} callback - Callback after request is complete.