code: function getHostname(url, userOptions = {}) {
    const defaults = {
      removeSubdomains: true,
    };
    const options = Object.assign({}, defaults, userOptions);
    const domainRegExp = /^(?:[a-z]+:\/\/)?(?:[^/@]+@)?([^/:]+)/i;
    const ipAddressRegExp = /^\d{1,3}\.\d{1,3}.\d{1,3}\.\d{1,3}$/;
    const domainMatch = url.match(domainRegExp);
  
    if (domainMatch === null) {
      throw new Error(`URL is invalid: ${url}`);
    }
  
    // If the hostname is an IP address, no further processing can be done.
    const hostname = domainMatch[1];
    if (ipAddressRegExp.test(hostname)) {
      return hostname;
    }
  
    // Return the hostname with subdomains removed, if requested.
    return (options.removeSubdomains) ? removeSubdomains(hostname) : hostname;
  }
docs: Isolate the domain name of a URL.