Issue 6989 - Optimize CSS rule generation

lib/elemHide.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 258 matching lines @@
   // calculate the sizes of the selectors and divide them up accordingly, but
   // this approach is more efficient and has worked well in practice. In theory
   // this could still lead to some selectors not working on Chromium, but it is
   // highly unlikely.
   // See issue #6298 and https://crbug.com/804179
   for (let i = 0; i < selectors.length; i += selectorGroupSize)
     yield selectors.slice(i, i + selectorGroupSize);
 }
 
 /**
- * Creates element hiding CSS rules for a given list of selectors. Each rule
- * contains no more than the maximum number of selectors as determined by the
- * value of <code>{@link selectorGroupSize}</code>.
+ * Creates an element hiding CSS rule for a given list of selectors.
  *
  * @param {Array.<string>} selectors
- * @yields {string}
+ * @returns {string}
  */
-function* createRules(selectors)
+function createRule(selectors)
 {
-  for (let selectorGroup of splitSelectors(selectors))
-    yield selectorGroup.join(", ") + " {display: none !important;}";
+  let rule = "";
+
+  for (let i = 0; i < selectors.length - 1; i++)

[Manish Jethani, 2018/09/26 15:29:56]

I tried a few things here:

 1.  Used `for...of` and sliced out the ", " at the end before appending "
{display: none !important;}\n"
 2.  Used `selectors.pop()`, a `for...of` loop, and concatenated the last
element in the array at the end
 3.  Used a regular `for` loop until the second to last entry, then concatenated
the last entry at the end

The last one (which is in the current patch) performs the best.

[hub, 2018/09/26 16:49:11]

Acknowledged.

+    rule += selectors[i] + ", ";
+
+  rule += selectors[selectors.length - 1] + " {display: none !important;}\n";
+
+  return rule;
 }
 
 /**
  * Creates an element hiding CSS style sheet from a given list of selectors.
  * @param {Array.<string>} selectors
  * @returns {string}
  */
 function createStyleSheet(selectors)
 {
   let styleSheet = "";
 
-  for (let rule of createRules(selectors))
-    styleSheet += rule + "\n";
+  for (let selectorGroup of splitSelectors(selectors))
+    styleSheet += createRule(selectorGroup);
 
   return styleSheet;
 }
 
 exports.createStyleSheet = createStyleSheet;