1 files changed, 70 insertions, 0 deletions
diff --git a/data/extensions/uBlock0@raymondhill.net/js/scriptlets/dom-survey-elements.js b/data/extensions/uBlock0@raymondhill.net/js/scriptlets/dom-survey-elements.js
new file mode 100644
index 0000000..85270ce
--- /dev/null
+++ b/data/extensions/uBlock0@raymondhill.net/js/scriptlets/dom-survey-elements.js
@@ -0,0 +1,70 @@
+/*******************************************************************************
+
+    uBlock Origin - a comprehensive, efficient content blocker
+    Copyright (C) 2015-present Raymond Hill
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see {http://www.gnu.org/licenses/}.
+
+    Home: https://github.com/gorhill/uBlock
+*/
+
+/******************************************************************************/
+
+// https://github.com/uBlockOrigin/uBlock-issues/issues/756
+//   Keep in mind CPU usage with large DOM and/or filterset.
+
+(( ) => {
+    if ( typeof vAPI !== 'object' ) { return; }
+
+    const t0 = Date.now();
+
+    if ( vAPI.domSurveyElements instanceof Object === false ) {
+        vAPI.domSurveyElements = {
+            busy: false,
+            hiddenElementCount: Number.NaN,
+            surveyTime: t0,
+        };
+    }
+    const surveyResults = vAPI.domSurveyElements;
+
+    if ( surveyResults.busy ) { return; }
+    surveyResults.busy = true;
+
+    if ( surveyResults.surveyTime < vAPI.domMutationTime ) {
+        surveyResults.hiddenElementCount = Number.NaN;
+    }
+    surveyResults.surveyTime = t0;
+
+    if ( isNaN(surveyResults.hiddenElementCount) ) {
+        surveyResults.hiddenElementCount = (( ) => {
+            if ( vAPI.domFilterer instanceof Object === false ) { return 0; }
+            const details = vAPI.domFilterer.getAllSelectors(0b11);
+            if (
+                Array.isArray(details.declarative) === false ||
+                details.declarative.length === 0
+            ) {
+                return 0;
+            }
+            return document.querySelectorAll(
+                details.declarative.join(',\n')
+            ).length;
+        })();
+    }
+
+    surveyResults.busy = false;
+
+    // IMPORTANT: This is returned to the injector, so this MUST be
+    //            the last statement.
+    return surveyResults.hiddenElementCount;
+})();