Issue 6727 - Use string rather than map for single-domain filters

lib/elemHide.js

Index: lib/elemHide.js
===================================================================
--- a/lib/elemHide.js
+++ b/lib/elemHide.js
@@ -67,16 +67,20 @@
 
 /**
  * Adds a filter to the lookup table of filters by domain.
  * @param {Filter} filter
  */
 function addToFiltersByDomain(filter)
 {
   let domains = filter.domains || defaultDomains;
+
+  if (typeof domains == "string")

[sergei, 2018/05/28 09:22:07]

Will the refactoring of that `typeof DOMAINS == "string"` with the applying of
an action for each domain significantly negatively affect performance and the
memory usage?

I'm also not a big fan of spreading the logic
let defaultDomains = new Map([["", true]]);
and
domains = [[domains, true]];
among files, IMO it would be better to keep it in filter classes.

[kzar, 2018/06/05 16:51:30]

Agreed, if possible (without messing up performance / memory usage) that would
be nice.

+    domains = [[domains, true]];
+
   for (let [domain, isIncluded] of domains)
   {
     // There's no need to note that a filter is generically disabled.
     if (!isIncluded && domain == "")
       continue;
 
     let filters = filtersByDomain.get(domain);
     if (!filters)
@@ -183,17 +187,21 @@
     {
       filterBySelector.delete(filter.selector);
       unconditionalSelectors = null;
     }
     // Conditionally applied element hiding filters
     else
     {
       let domains = filter.domains || defaultDomains;
-      for (let domain of domains.keys())
+
+      if (typeof domains == "string")
+        domains = [[domains]];
+
+      for (let [domain] of domains)
       {
         let filters = filtersByDomain.get(domain);
         if (filters)
           filters.delete(filter);
       }
     }
 
     knownFilters.delete(filter);