Issue 7250 - Optimize third-party request check

lib/domain.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-present eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 67 matching lines @@
 
 /**
  * Gets the base domain for the given hostname.
  *
  * @param {string} hostname
  * @returns {string}
  */
 function getDomain(hostname)
 {
   let slices = [];
-  let cutoff = null;
+  let cutoff = NaN;
 
   for (let suffix of suffixes(hostname))
   {
     slices.push(suffix);
 
     let offset = publicSuffixMap.get(suffix);
 
     if (typeof offset != "undefined")
     {
       cutoff = slices.length - 1 - offset;
       break;
     }
   }
 
-  if (cutoff == null)
+  if (isNaN(cutoff))
     return slices.length > 2 ? slices[slices.length - 2] : hostname;
 
   if (cutoff <= 0)
     return hostname;
 
   return slices[cutoff];
 }
 
 exports.getDomain = getDomain;
 
@@ skipping 18 matching lines @@
   if (requestHostname == documentHostname)
     return false;
 
   if (!isDomain(requestHostname) || !isDomain(documentHostname))
     return true;
 
   return getDomain(requestHostname) != getDomain(documentHostname);
 }
 
 exports.isThirdParty = isThirdParty;