Noissue - Avoid redundant lookup in keyword-by-filter map

lib/matcher.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-present eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 328 matching lines @@
   /**
    * Checks whether a particular filter is slow
    * @param {RegExpFilter} filter
    * @returns {boolean}
    */
   isSlowFilter(filter)
   {
     let matcher = (
       filter instanceof WhitelistFilter ? this.whitelist : this.blacklist
     );
-    if (matcher.hasFilter(filter))
-      return !matcher.getKeywordForFilter(filter);
+    let keyword = matcher.getKeywordForFilter(filter);
+    if (keyword != null)
+      return keyword == "";

[Manish Jethani, 2018/09/18 14:10:26]

Well hold on, if we change this here to `keyword == ""` then we should also
change the condition in the following line of code, because it too never returns
null, just an empty string.

I'm iffy about this. I think `!keyword` is fine. Do we agree on this?

     return !matcher.findKeyword(filter);
   }
 
   /**
    * Optimized filter matching testing both whitelist and blacklist matchers
    * simultaneously. For parameters see
      {@link Matcher#matchesAny Matcher.matchesAny()}.
    * @see Matcher#matchesAny
    * @inheritdoc
    */
@@ skipping 52 matching lines @@
 
 exports.CombinedMatcher = CombinedMatcher;
 
 /**
  * Shared {@link CombinedMatcher} instance that should usually be used.
  * @type {CombinedMatcher}
  */
 let defaultMatcher = new CombinedMatcher();
 
 exports.defaultMatcher = defaultMatcher;