Issue 5735 - Use JS Map instead of Object for global keyByFilter in elemHide.js

lib/elemHide.js

Index: lib/elemHide.js
diff --git a/lib/elemHide.js b/lib/elemHide.js
index e99bb8a7f269e4df2370fb95bd950031503540b4..c38a5cd142a5cd36b6432a351f30370df1cf5ed4 100644
--- a/lib/elemHide.js
+++ b/lib/elemHide.js
@@ -31,10 +31,10 @@ const {FilterNotifier} = require("filterNotifier");
 let filterByKey = [];
 
 /**
- * Lookup table, keys of the filters by filter text
- * @type {Object}
+ * Lookup table, keys of the filters by filter
+ * @type {Map.<Filter,string>}
  */
-let keyByFilter = Object.create(null);
+let keyByFilter = new Map();
 
 /**
  * Nested lookup table, filter (or false if inactive) by filter key by domain.
@@ -91,7 +91,7 @@ let ElemHide = exports.ElemHide = {
   clear()
   {
     filterByKey = [];
-    keyByFilter = Object.create(null);
+    keyByFilter = new Map();
     filtersByDomain = new Map();
     filterKeyBySelector = Object.create(null);
     unconditionalSelectors = unconditionalFilterKeys = null;
@@ -143,11 +143,11 @@ let ElemHide = exports.ElemHide = {
     }
     else
     {
-      if (filter.text in keyByFilter)
+      if (keyByFilter.has(filter))
         return;
 
       let key = filterByKey.push(filter) - 1;
-      keyByFilter[filter.text] = key;
+      keyByFilter.set(filter, key);
 
       if (!(filter.domains || filter.selector in exceptions))
       {
@@ -204,12 +204,12 @@ let ElemHide = exports.ElemHide = {
     }
     else
     {
-      if (!(filter.text in keyByFilter))
+      let key = keyByFilter.get(filter);
+      if (typeof key == "undefined")
         return;
 
-      let key = keyByFilter[filter.text];
       delete filterByKey[key];
-      delete keyByFilter[filter.text];
+      keyByFilter.delete(filter);
       this._removeFilterKey(key, filter);
     }