Issue 6434 - Reimplement positionInParent with indexOf

lib/coreUtils.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 16 matching lines @@
 
   return descriptor;
 }
 exports.desc = desc;
 
 function extend(cls, properties)
 {
   return Object.create(cls.prototype, desc(properties));
 }
 exports.extend = extend;
+
+function findIndex(iterable, callback, thisArg)
+{
+  let index = 0;
+  for (let item of iterable)
+  {
+    if (callback.call(thisArg, item))
+      return index;
+
+    index++;
+  }
+
+  return -1;
+}
+exports.findIndex = findIndex;
+
+function indexOf(iterable, searchElement)
+{
+  return findIndex(iterable, item => item === searchElement);
+}
+exports.indexOf = indexOf;