From 7a023077b34e0eef509638a6db866f4326e5ff7b Mon Sep 17 00:00:00 2001
From: gorhill <rhill@raymondhill.net>
Date: Sun, 12 Mar 2017 10:22:46 -0400
Subject: [PATCH] performance work for pseudo-user styles code

---
 src/js/contentscript.js | 80 +++++++++++++++++++++++++----------------
 1 file changed, 50 insertions(+), 30 deletions(-)

diff --git a/src/js/contentscript.js b/src/js/contentscript.js
index c4d29e574..e11d868cb 100644
--- a/src/js/contentscript.js
+++ b/src/js/contentscript.js
@@ -229,55 +229,75 @@ var platformHideNode = vAPI.hideNode,
     }
 
     var uid,
-        timerId,
+        timer,
         observer,
-        changedNodes = [];
-    var observerOptions = {
+        changedNodes = [],
+        observerOptions = {
         attributes: true,
         attributeFilter: [ 'style' ]
     };
 
-    var overrideInlineStyle = function(node) {
-        var style = window.getComputedStyle(node),
-            display = style.getPropertyValue('display'),
-            attr = node.getAttribute('style') || '';
-        if ( node[uid] === undefined ) {
-            node[uid] = node.hasAttribute('style') && attr;
+    // https://jsperf.com/clientheight-and-clientwidth-vs-getcomputedstyle
+    //   Avoid getComputedStyle(), detecting whether a node is visible can be
+    //   achieved with clientWidth/clientHeight.
+    // https://gist.github.com/paulirish/5d52fb081b3570c81e3a
+    //   Do not interleave read-from/write-to the DOM. Write-to DOM
+    //   operations would cause the first read-from to be expensive, and
+    //   interleaving means that potentially all single read-from operation
+    //   would be expensive rather than just the 1st one.
+    //   Benchmarking toggling off/on cosmetic filtering confirms quite an
+    //   improvement when:
+    //   - batching as much as possible handling of all nodes;
+    //   - avoiding to interleave read-from/write-to operations.
+    //   However, toggling off/on cosmetic filtering repeatedly is not
+    //   a real use case, but this shows this will help performance
+    //   on sites which try to use inline styles to bypass blockers.
+    var batchProcess = function() {
+        timer.clear();
+        var cNodes = changedNodes, i = cNodes.length,
+            vNodes = [], j = 0,
+            node;
+        while ( i-- ) {
+            node = cNodes[i];
+            if ( node[uid] !== undefined && node.clientHeight && node.clientWidth ) {
+                vNodes[j++] = node;
+            }
         }
-        if ( display !== '' && display !== 'none' ) {
-            if ( attr !== '' ) { attr += '; '; }
+        cNodes.length = 0;
+        while ( j-- ) {
+            node = vNodes[j];
+            var attr = node.getAttribute('style');
+            if ( !attr ) {
+                attr = '';
+            } else {
+                attr += '; ';
+            }
             node.setAttribute('style', attr + 'display: none !important;');
         }
     };
 
-    var timerHandler = function() {
-        timerId = undefined;
-        var nodes = changedNodes,
-            i = nodes.length, node;
-        while ( i-- ) {
-            node = nodes[i];
-            if ( node[uid] !== undefined ) {
-                overrideInlineStyle(node);
-            }
-        }
-        nodes.length = 0;
-    };
-
     var observerHandler = function(mutations) {
-        var i = mutations.length;
+        var i = mutations.length,
+            cNodes = changedNodes,
+            j = cNodes.length;
         while ( i-- ) {
-            changedNodes.push(mutations[i].target);
-        }
-        if ( timerId === undefined ) {
-            timerId = vAPI.setTimeout(timerHandler, 1);
+            cNodes[j++] = mutations[i].target;
         }
+        timer.start();
     };
 
     platformHideNode = function(node) {
         if ( uid === undefined ) {
             uid = vAPI.randomToken();
+            timer = new vAPI.SafeAnimationFrame(batchProcess);
         }
-        overrideInlineStyle(node);
+        if ( node[uid] === undefined ) {
+            node[uid] = node.hasAttribute('style') && (node.getAttribute('style') || '');
+        }
+        // Performance: batch-process nodes to hide.
+        var cNodes = changedNodes;
+        cNodes[cNodes.length] = node;
+        timer.start();
         if ( observer === undefined ) {
             observer = new MutationObserver(observerHandler);
         }