Issue 6437 - Cache pattern attributes

lib/content/elemHideEmulation.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 20 matching lines @@
 {
   let {children} = node.parentNode;
   for (let i = 0; i < children.length; i++)
     if (children[i] == node)
       return i + 1;
   return 0;
 }
 
 function getCachedPropertyValue(object, name, defaultValueFunc = () => {})
 {
-  if (!(name in object))
-    Object.defineProperty(object, name, {value: defaultValueFunc()});
-  return object[name];

[hub, 2018/03/07 23:11:30]

here I would rather do something like:

let value = object[name];
if (value == undefined)
{
   value = defaultValueFunc();
   Object.defineProperty(object, name, {value});
}
return value;

The `in` operator is slower than `[]` and then we avoid a second lookup in the
fast path (hitting the cache).

[Manish Jethani, 2018/03/08 15:29:58]

Thanks, this is a good idea.

Done.

(I'm using strict equality to compare the cached value though since the value
could genuinely be null).

+  let value = object[name];
+  if (value === undefined)
+  {
+    value = defaultValueFunc();
+    Object.defineProperty(object, name, {value});
+  }
+  return value;
 }
 
 function makeSelector(node, selector)
 {
   if (node == null)
     return null;
   if (!node.parentElement)
   {
     let newSelector = ":root";
     if (selector)
@@ skipping 780 matching lines @@
           characterData: shouldObserveCharacterData(this.patterns),
           subtree: true
         }
       );
       this.document.addEventListener("load", this.onLoad.bind(this), true);
     }
   }
 };
 
 exports.ElemHideEmulation = ElemHideEmulation;