Issue 5735 - Use JS Map instead of Object for Filter.knownFilters

lib/filterClasses.js

Index: lib/filterClasses.js
diff --git a/lib/filterClasses.js b/lib/filterClasses.js
index 626eabad9538553550f08df724b14fbd077cd08b..417e4d8df3cc13fdd4daa0d6ac14489ad73b92cb 100644
--- a/lib/filterClasses.js
+++ b/lib/filterClasses.js
@@ -79,9 +79,9 @@ Filter.prototype =
 
 /**
  * Cache for known filters, maps string representation to filter objects.
- * @type {Object}
+ * @type {Map.<string,Filter>}
  */
-Filter.knownFilters = Object.create(null);
+Filter.knownFilters = new Map();
 
 /**
  * Regular expression that element hiding filters should match
@@ -108,10 +108,10 @@ Filter.optionsRegExp = /\$(~?[\w-]+(?:=[^,\s]+)?(?:,~?[\w-]+(?:=[^,\s]+)?)*)$/;
  */
 Filter.fromText = function(text)
 {
-  if (text in Filter.knownFilters)
-    return Filter.knownFilters[text];
+  let ret = Filter.knownFilters.get(text);
+  if (ret)

[kzar, 2017/09/20 12:30:24]

Just an observation since I don't think it matters, but this behaviour is
slightly different. If we cached a falsey value for a filter previously we would
have returned it but now we won't.

+    return ret;
 
-  let ret;
   let match = (text.includes("#") ? Filter.elemhideRegExp.exec(text) : null);
   if (match)
   {
@@ -136,7 +136,7 @@ Filter.fromText = function(text)
   else
     ret = RegExpFilter.fromText(text);
 
-  Filter.knownFilters[ret.text] = ret;
+  Filter.knownFilters.set(ret.text, ret);
   return ret;
 };