function poll(selector, callback, interval = 50, expiration = 20000) {

  // If element found, call callbacks
  if (typeof window.$ === 'function' && $.fn && $(selector).length) {

    callback($(selector));

  // If time has expired, return
  } else if (expiration <= 0) {

    return;

  // Otherwise, try again and decrement expiration
  } else {
    expiration -= interval;
    return setTimeout(pollForElement.bind(null, selector, callback, interval, expiration), interval);
  }

}