static resolveUrl(url, baseUrl) {
    url = trim(url);
    if (!url) return null;
    if (startsWith(url, '#')) return null;
    const { protocol } = parse(url);
    if (includes(['http:', 'https:'], protocol)) {
      return url.split('#')[0];
    } else if (!protocol) { // eslint-disable-line no-else-return
      return resolve(baseUrl, url).split('#')[0];
    }
    return null;
  }
@param {!string} url
@param {!string} baseUrl
@return {!string}