appendHash(url, hash) {
    if (!url) {
      return url;
    }

    return url + (url.indexOf("?") === -1 ? "?" : "&") + hash;
  }
Appends a cache busting hash to the query string of the url
E.g. http://localhost:8080/ -> http://localhost:8080/?50c9096ba6183fd728eeb065a26ec175

@private
@param {string | undefined} url
@param {string} hash