Issue 5735 - Use JS Map instead of Object for property domains of Filter objects

lib/elemHide.js

Index: lib/elemHide.js
diff --git a/lib/elemHide.js b/lib/elemHide.js
index e9243853e3733c83632710b690e69224f1983bea..3b0a9402eafe19fe2cd07539fe57e98e356a09ec 100644
--- a/lib/elemHide.js
+++ b/lib/elemHide.js
@@ -66,8 +66,8 @@ let unconditionalFilterKeys = null;
 /**
  * Object to be used instead when a filter has a blank domains property.
  */
-let defaultDomains = Object.create(null);
-defaultDomains[""] = true;
+let defaultDomains = new Map();
+defaultDomains.set("", true);

[Wladimir Palant, 2017/09/21 08:11:44]

You can initialize the Map object immediately: new Map([["", true]])

[sergei, 2017/09/21 10:50:33]

Done.

 
 /**
  * Lookup table, keys are known element hiding exceptions
@@ -104,13 +104,13 @@ let ElemHide = exports.ElemHide = {
   _addToFiltersByDomain(key, filter)
   {
     let domains = filter.domains || defaultDomains;
-    for (let domain in domains)
+    for (let [domain, isIncluded] of domains)
     {
       let filters = filtersByDomain[domain];
       if (!filters)
         filters = filtersByDomain[domain] = Object.create(null);

[Wladimir Palant, 2017/09/21 08:11:44]

Shouldn't this be turned in to a Map object as well while we are at it?

[sergei, 2017/09/21 10:50:33]

No, I find the change of filtersByDomain self-contained enough because the
current change is rather aimed at filterClasses module and the change in
elemHide.js is a consequence. In addition smaller commits are always better, for
instance we can easier compare the contribution in the performance and memory
usage from a change of type of one object with many entries with the change of
types of many objects with not so many entries.

 
-      if (domains[domain])
+      if (isIncluded)
         filters[key] = filter;
       else
         filters[key] = false;
@@ -182,7 +182,7 @@ let ElemHide = exports.ElemHide = {
     // We haven't found this filter in unconditional filters, look in
     // filtersByDomain.
     let domains = filter.domains || defaultDomains;
-    for (let domain in domains)
+    for (let domain of domains.keys())
     {
       let filters = filtersByDomain[domain];
       if (filters)