Issue 6434 - Reimplement positionInParent with indexOf

lib/content/elemHideEmulation.js

Index: lib/content/elemHideEmulation.js
===================================================================
--- a/lib/content/elemHideEmulation.js
+++ b/lib/content/elemHideEmulation.js
@@ -13,32 +13,29 @@
  *
  * You should have received a copy of the GNU General Public License
  * along with Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
  */
 
 "use strict";
 
 const {textToRegExp, filterToRegExp, splitSelector} = require("../common");
+const {findIndex} = require("../coreUtils");
 
 let MIN_INVOCATION_INTERVAL = 3000;
 const MAX_SYNCHRONOUS_PROCESSING_TIME = 50;
 const abpSelectorRegexp = /:-abp-([\w-]+)\(/i;
 
 /** Return position of node from parent.
  * @param {Node} node the node to find the position of.
  * @return {number} One-based index like for :nth-child(), or 0 on error.
  */
 function positionInParent(node)
 {
-  let {children} = node.parentNode;
-  for (let i = 0; i < children.length; i++)
-    if (children[i] == node)
-      return i + 1;
-  return 0;
+  return findIndex(node.parentNode.children, child => child == node) + 1;
 }
 
 function makeSelector(node, selector)
 {
   if (node == null)
     return null;
   if (!node.parentElement)
   {