code: function isSubdomainOf(subdomain, host) {
  
          // Comparisons must be case-insensitive
          subdomain   = subdomain.toLowerCase();
          host        = host.toLowerCase();
  
          // If we're ignoring www, remove it from both
          // (if www is the first domain component...)
          if (crawler.ignoreWWWDomain) {
              subdomain = subdomain.replace(/^www./ig, "");
              host = host.replace(/^www./ig, "");
          }
  
          // They should be the same flipped around!
          return subdomain.split("").reverse().join("").substr(0, host.length) ===
                  host.split("").reverse().join("");
      }
docs: Checks if the first domain is a subdomain of the second