Node Mutation Hook Library

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Node Mutation Hook Library

A wrapper around MutationObserver to hook into creation of elements (filtered on CSS selector) or removal of nodes.

This script should not be not be installed directly. It is a library for other scripts to include with the meta directive // @require https://update.greatest.deepsurf.us/scripts/565361/1853994/Node%20Mutation%20Hook%20Library.js

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// ==UserScript==
// @name        Node Mutation Hook Library
// @namespace   https://greatest.deepsurf.us/users/1545341
// @version     3.0.1
// @license     MIT
// @author      abcenjoyer
// @description A wrapper around MutationObserver to hook into creation of elements (filtered on CSS selector) or removal of nodes.
// ==/UserScript==

/*
 * Copyright (c) 2026 abcenjoyer
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

// callbacks should return a truthy value when they want no more elements to be processed, and falsy value when they want to continue processing
function hookCreation(selector, callback, callbackOnExisting) {
  const observerTarget = document.documentElement;

  if (callbackOnExisting) {
    for (const element of observerTarget.querySelectorAll(selector)) {
      if (callback(element)) {
        return;
      }
    }
  }

  const observer = new MutationObserver((mutations) => {
    for (const record of mutations) {
      for (const node of record.addedNodes) {
        if (node.nodeType === Node.ELEMENT_NODE) {
          if (node.matches(selector)) {
            if (callback(node)) {
              observer.disconnect();
              return;
            }
          }

          for (const element of node.querySelectorAll(selector)) {
            if (callback(element)) {
              observer.disconnect();
              return;
            }
          }
        }
      }
    }
  });

  observer.observe(observerTarget, {
    childList: true,
    subtree: true
  });
}

function hookRemoval(targetNode, callback) {
  const observer = new MutationObserver((mutations) => {
    for (const record of mutations) {
      for (const node of record.removedNodes) {
          if (node.contains(targetNode)) {
            observer.disconnect();
            callback();
          }
      }
    }
  });

  // observing the entire document is required because if targetNode is deleted because an ancestor node was, observing the parent won't work
  observer.observe(document, {
    childList: true,
    subtree: true
  });
}