Issue 4057 - Use Set for seenFilters, number for key

Author: kzar

lib/elemHide.js

@@ -31,7 +31,7 @@ var {FilterNotifier} = require("filterNotifier");
  * Lookup table, filters by their associated key
  * @type Object
  */
-var filterByKey = [];
+var filterByKey = Object.create(null);
 
 /**
  * Lookup table, keys of the filters by filter text
@@ -47,7 +47,7 @@ var keyByFilter = Object.create(null);
 var usingGetSelectorsForDomain = !("nsIStyleSheetService" in Ci);
 
 /**
- * Nested lookup table, filter (or false if inactive) by filter text by domain.
+ * Nested lookup table, filter (or false if inactive) by filter key by domain.
  * (Only contains filters that aren't unconditionally matched for all domains.)
  * @type Object
  */
@@ -125,7 +125,7 @@ var ElemHide = exports.ElemHide =
    */
   clear: function()
   {
-    filterByKey = [];
+    filterByKey = Object.create(null);
     keyByFilter = Object.create(null);
     filtersByDomain = Object.create(null);
     filtersBySelector = Object.create(null);
@@ -192,7 +192,12 @@ var ElemHide = exports.ElemHide =
       if (filter.text in keyByFilter)
         return;
 
-      let key = filterByKey.push(filter) - 1;
+      let key;
+      do {
+        key = Math.random() * 0x0FFFFFFF | 0;
+      } while (key in filterByKey);
+
+      filterByKey[key] = filter;
       keyByFilter[filter.text] = key;
 
       if (usingGetSelectorsForDomain)
@@ -482,7 +487,7 @@ var ElemHide = exports.ElemHide =
 
     let selectors = [];
 
-    let seenFilters = Object.create(null);
+    let seenFilters = new Set();
     let currentDomain = domain ? domain.toUpperCase() : "";
     while (true)
     {
@@ -494,9 +499,9 @@ var ElemHide = exports.ElemHide =
       {
         for (let filterKey in filters)
         {
-          if (filterKey in seenFilters)
+          if (seenFilters.has(filterKey))
             continue;
-          seenFilters[filterKey] = true;
+          seenFilters.add(filterKey);
 
           let filter = filters[filterKey];
           if (filter && !this.getException(filter, domain))