Issue 6559 - Use maps and sets where appropriate

lib/elemHide.js

Index: lib/elemHide.js
===================================================================
--- a/lib/elemHide.js
+++ b/lib/elemHide.js
@@ -21,38 +21,39 @@
  * @fileOverview Element hiding implementation.
  */
 
 const {ElemHideException} = require("./filterClasses");
 const {FilterNotifier} = require("./filterNotifier");
 
 /**
  * Lookup table, filters by their associated key
- * @type {Object}
+ * @type {Filter[]}
  */
 let filterByKey = [];
 
 /**
  * Lookup table, keys of the filters by filter
- * @type {Map.<Filter,string>}
+ * @type {Map.<Filter,number>}
  */
 let keyByFilter = new Map();
 
 /**
  * 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 {Map.<string,Map.<string,(Filter|boolean)>>}
+ * @type {Map.<string,Map.<number,(Filter|boolean)>>}
  */
 let filtersByDomain = new Map();
 
 /**
  * Lookup table, filter key by selector. (Only used for selectors that are
  * unconditionally matched for all domains.)
+ * @type {Map.<string,number>}
  */
-let filterKeyBySelector = Object.create(null);
+let filterKeyBySelector = new Map();
 
 /**
  * This array caches the keys of filterKeyBySelector table (selectors which
  * unconditionally apply on all domains). It will be null if the cache needs to
  * be rebuilt.
  */
 let unconditionalSelectors = null;
 
@@ -64,44 +65,44 @@
 let unconditionalFilterKeys = null;
 
 /**
  * Object to be used instead when a filter has a blank domains property.
  */
 let defaultDomains = new Map([["", true]]);
 
 /**
- * Lookup table, keys are known element hiding exceptions
- * @type {Object}
+ * Set containing known element hiding exceptions
+ * @type {Set.<string>}
  */
-let knownExceptions = Object.create(null);
+let knownExceptions = new Set();
 
 /**
  * Lookup table, lists of element hiding exceptions by selector
- * @type {Object}
+ * @type {Map.<string,Filter>}
  */
-let exceptions = Object.create(null);
+let exceptions = new Map();
 
 /**
  * Container for element hiding filters
  * @class
  */
 let ElemHide = exports.ElemHide = {
   /**
    * Removes all known filters
    */
   clear()
   {
+    for (let collection of [keyByFilter, filtersByDomain, filterKeyBySelector,
+                            knownExceptions, exceptions])
+    {
+      collection.clear();
+    }
     filterByKey = [];
-    keyByFilter = new Map();
-    filtersByDomain = new Map();
-    filterKeyBySelector = Object.create(null);
     unconditionalSelectors = unconditionalFilterKeys = null;
-    knownExceptions = Object.create(null);
-    exceptions = Object.create(null);
     FilterNotifier.emit("elemhideupdate");
   },
 
   _addToFiltersByDomain(key, filter)
   {
     let domains = filter.domains || defaultDomains;
     for (let [domain, isIncluded] of domains)
     {
@@ -115,66 +116,68 @@
   /**
    * Add a new element hiding filter
    * @param {ElemHideFilter} filter
    */
   add(filter)
   {
     if (filter instanceof ElemHideException)
     {
-      if (filter.text in knownExceptions)
+      if (knownExceptions.has(filter.text))
         return;
 
       let {selector} = filter;
-      if (!(selector in exceptions))
-        exceptions[selector] = [];
-      exceptions[selector].push(filter);
+      let list = exceptions.get(selector);
+      if (list)
+        list.push(filter);
+      else
+        exceptions.set(selector, [filter]);
 
       // If this is the first exception for a previously unconditionally
       // applied element hiding selector we need to take care to update the
       // lookups.
-      let filterKey = filterKeyBySelector[selector];
+      let filterKey = filterKeyBySelector.get(selector);
       if (typeof filterKey != "undefined")
       {
         this._addToFiltersByDomain(filterKey, filterByKey[filterKey]);
-        delete filterKeyBySelector[selector];
+        filterKeyBySelector.delete(selector);
         unconditionalSelectors = unconditionalFilterKeys = null;
       }
 
-      knownExceptions[filter.text] = true;
+      knownExceptions.add(filter.text);
     }
     else
     {
       if (keyByFilter.has(filter))
         return;
 
       let key = filterByKey.push(filter) - 1;
       keyByFilter.set(filter, key);
 
-      if (!(filter.domains || filter.selector in exceptions))
+      if (!(filter.domains || exceptions.has(filter.selector)))
       {
         // The new filter's selector is unconditionally applied to all domains
-        filterKeyBySelector[filter.selector] = key;
+        filterKeyBySelector.set(filter.selector, key);
         unconditionalSelectors = unconditionalFilterKeys = null;
       }
       else
       {
         // The new filter's selector only applies to some domains
         this._addToFiltersByDomain(key, filter);
       }
     }
 
     FilterNotifier.emit("elemhideupdate");
   },
 
   _removeFilterKey(key, filter)
   {
-    if (filterKeyBySelector[filter.selector] == key)
+    if (filterKeyBySelector.get(filter.selector) == key)
     {
-      delete filterKeyBySelector[filter.selector];
+      filterKeyBySelector.delete(filter.selector);
       unconditionalSelectors = unconditionalFilterKeys = null;
       return;
     }
 
     // We haven't found this filter in unconditional filters, look in
     // filtersByDomain.
     let domains = filter.domains || defaultDomains;
     for (let domain of domains.keys())
@@ -188,24 +191,24 @@
   /**
    * Removes an element hiding filter
    * @param {ElemHideFilter} filter
    */
   remove(filter)
   {
     if (filter instanceof ElemHideException)
     {
-      if (!(filter.text in knownExceptions))
+      if (!knownExceptions.has(filter.text))
         return;
 
-      let list = exceptions[filter.selector];
+      let list = exceptions.get(filter.selector);
       let index = list.indexOf(filter);
       if (index >= 0)
         list.splice(index, 1);
-      delete knownExceptions[filter.text];
+      knownExceptions.delete(filter.text);
     }
     else
     {
       let key = keyByFilter.get(filter);
       if (typeof key == "undefined")
         return;
 
       delete filterByKey[key];
@@ -220,20 +223,20 @@
    * Checks whether an exception rule is registered for a filter on a particular
    * domain.
    * @param {Filter} filter
    * @param {string} docDomain
    * @return {ElemHideException}
    */
   getException(filter, docDomain)
   {
-    if (!(filter.selector in exceptions))
+    let list = exceptions.get(filter.selector);
+    if (!list)
       return null;
 
-    let list = exceptions[filter.selector];
     for (let i = list.length - 1; i >= 0; i--)
     {
       if (list[i].isActiveOnDomain(docDomain))
         return list[i];
     }
 
     return null;
   },
@@ -276,33 +279,33 @@
 
   /**
    * Returns a list of selectors that apply on each website unconditionally.
    * @returns {string[]}
    */
   getUnconditionalSelectors()
   {
     if (!unconditionalSelectors)
-      unconditionalSelectors = Object.keys(filterKeyBySelector);
+      unconditionalSelectors = [...filterKeyBySelector.keys()];
     return unconditionalSelectors.slice();
   },
 
   /**
    * Returns a list of filter keys for selectors which apply to all websites
    * without exception.
    * @returns {number[]}
    */
   getUnconditionalFilterKeys()
   {
     if (!unconditionalFilterKeys)
     {
       let selectors = this.getUnconditionalSelectors();
       unconditionalFilterKeys = [];
       for (let selector of selectors)
-        unconditionalFilterKeys.push(filterKeyBySelector[selector]);
+        unconditionalFilterKeys.push(filterKeyBySelector.get(selector));
     }
     return unconditionalFilterKeys.slice();
   },
 
 
   /**
    * Constant used by getSelectorsForDomain to return all selectors applying to
    * a particular hostname.
@@ -346,31 +349,31 @@
     if (criteria < ElemHide.NO_UNCONDITIONAL)
     {
       selectors = this.getUnconditionalSelectors();
       if (provideFilterKeys)
         filterKeys = this.getUnconditionalFilterKeys();
     }
 
     let specificOnly = (criteria >= ElemHide.SPECIFIC_ONLY);
-    let seenFilters = Object.create(null);
+    let seenFilters = new Set();
     let currentDomain = domain ? domain.toUpperCase() : "";
     while (true)
     {
       if (specificOnly && currentDomain == "")
         break;
 
       let filters = filtersByDomain.get(currentDomain);
       if (filters)
       {
         for (let [filterKey, filter] of filters)
         {
-          if (filterKey in seenFilters)
+          if (seenFilters.has(filterKey))
             continue;
-          seenFilters[filterKey] = true;
+          seenFilters.add(filterKey);
 
           if (filter && !this.getException(filter, domain))
           {
             selectors.push(filter.selector);
             // It is faster to always push the key, even if not required.
             filterKeys.push(filterKey);
           }
         }