Issue 6665 - Optimize element hiding emulation filter lookups

lib/common.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 83 matching lines @@
         start = i + 1;
       }
     }
   }
 
   selectors.push(selector.substring(start));
   return selectors;
 }
 
 exports.splitSelector = splitSelector;
+
+/**
+ * Yields subdomains of a domain
+ * @param {string} domain
+ * @yields {string}
+ */
+function* subdomains(domain)
+{
+  while (true)
+  {
+    let index = domain.indexOf(".");
+    if (index == -1)
+      break;
+
+    yield domain = domain.substring(index + 1);
+  }
+}
+
+exports.subdomains = subdomains;