Add trusted-create-element scriptlet

As discussed with filter list maintainers.

* @scriptlet trusted-create-element
*
* @description
* Element(s) from a parsed HTML string are added as child element(s) to a
* specific parent element in the DOM.
*
* @param parent
* A CSS selector identifying the element to which created element(s) will be
* added.
*
* @param html
* An HTML string to be parsed using DOMParser, and which resulting elements
* are to be added as child element(s).
*
* @param duration
* Optional. If specified, the time in ms after which the added elements will
* be removed. No removal will occur if not specified.

src/js/resources/create-element.js

@@ -0,0 +1,112 @@
+/*******************************************************************************
+
+    uBlock Origin - a comprehensive, efficient content blocker
+    Copyright (C) 2025-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
+
+*/
+
+import { registerScriptlet } from './base.js';
+import { safeSelf } from './safe-self.js';
+
+/******************************************************************************/
+
+/**
+ * @scriptlet trusted-create-element
+ * 
+ * @description
+ * Element(s) from a parsed HTML string are added as child element(s) to a
+ * specific parent element in the DOM.
+ * 
+ * @param parent
+ * A CSS selector identifying the element to which created element(s) will be
+ * added.
+ * 
+ * @param html
+ * An HTML string to be parsed using DOMParser, and which resulting elements
+ * are to be added as child element(s).
+ * 
+ * @param duration
+ * Optional. If specified, the time in ms after which the added elements will
+ * be removed. No removal will occur if not specified.
+ * 
+ * */
+
+function trustedCreateElement(
+    parentSelector,
+    htmlStr = '',
+    durationStr = ''
+) {
+    if ( parentSelector === '' ) { return; }
+    if ( htmlStr === '' ) { return; }
+    const safe = safeSelf();
+    const logPrefix = safe.makeLogPrefix('trusted-create-element', parentSelector, htmlStr, durationStr);
+    // We do not want to recursively create elements
+    self.trustedCreateElement = true;
+    let ancestor = self.frameElement;
+    while ( ancestor !== null ) {
+        const doc = ancestor.ownerDocument;
+        if ( doc === null ) { break; }
+        const win = doc.defaultView;
+        if ( win === null ) { break; }
+        if ( win.trustedCreateElement ) { return; }
+        ancestor = ancestor.frameElement;
+    }
+    const duration = parseInt(durationStr, 10);
+    const domParser = new DOMParser();
+    const externalDoc = domParser.parseFromString(htmlStr, 'text/html');
+    const docFragment = new DocumentFragment();
+    const toRemove = [];
+    for ( const external of externalDoc.querySelectorAll('body > *') ) {
+        const imported = document.adoptNode(external);
+        docFragment.append(imported);
+        if ( isNaN(duration) ) { continue; }
+        toRemove.push(imported);
+    }
+    if ( docFragment.childElementCount === 0 ) { return; }
+    const remove = ( ) => {
+        for ( const elem of toRemove ) {
+            elem.remove();
+        }
+        safe.uboLog(logPrefix, 'Element(s) removed');
+    };
+    const append = ( ) => {
+        const parent = document.querySelector(parentSelector);
+        if ( parent === null ) { return false; }
+        parent.append(docFragment);
+        safe.uboLog(logPrefix, 'Element(s) appended');
+        if ( toRemove.length === 0 ) { return true; }
+        setTimeout(remove, duration);
+        return true;
+    };
+    if ( append() ) { return; }
+    const observer = new MutationObserver(( ) => {
+        if ( append() === false ) { return; }
+        observer.disconnect();
+    });
+    observer.observe(document, { childList: true, subtree: true });
+}
+registerScriptlet(trustedCreateElement, {
+    name: 'trusted-create-element.js',
+    requiresTrust: true,
+    dependencies: [
+        safeSelf,
+    ],
+    world: 'ISOLATED',
+});
+
+/******************************************************************************/

src/js/resources/scriptlets.js

@@ -21,6 +21,7 @@
 */
 
 import './attribute.js';
+import './create-element.js';
 import './href-sanitizer.js';
 import './json-edit.js';
 import './json-prune.js';