regex-text-replacer.user.js

// ==UserScript==
// @name        Regex text replacer
// @version     1.0.2
// @description Replace any regex with any other text
// @match       http://*/*
// @match       https://*/*
// @match       file://*/*
// @author      voc
// @namespace   https://github.com/Vocaned
// @grant       none
// @run-at      document-end
// ==/UserScript==

// NOTE: The regex will always have /gi flags applied
const DICTIONARY = [
  [/\bfoot\b/, 'paw'],
  [/\bfeet\b/, 'paws']
];


(() => {
  const patterns = Object.fromEntries(DICTIONARY.map(e => [e[0].source, e[1]]));
  const replacementRegex = new RegExp(Object.keys(patterns).map(p => `(${p})`).join('|'), 'gi');

  const seenNodes = new WeakSet();
  function replaceTextNode(node) {
    if (seenNodes.has(node)) return;
    let changed = false;
    const newText = node.nodeValue.replace(replacementRegex, (...matches) => {
      for (let i = 1; i < matches.length - 2; i++) {
        if (matches[i] !== undefined) {
          changed = true;
          const newStr = patterns[Object.keys(patterns)[i - 1]];
          if (newStr === newStr.toLowerCase()) return matchCase(matches[i], newStr);
          return newStr;
        }
      }
    });
    if (changed) {
      node.nodeValue = newText;
      seenNodes.add(node);
    }
  }

  const elementBlacklist = ['script', 'style', 'noscript', 'textarea', 'input', 'template', 'svg'];
  function replaceElementNode(node) {
    if (node === null) return; // FIXME: what causes a null node to get here on some sites when manually replacing <title>?
    const walker = document.createTreeWalker(node, NodeFilter.SHOW_TEXT,
      {
        acceptNode: n => {
          if (n.parentNode && elementBlacklist.includes(n.parentNode.nodeName)) {
            return NodeFilter.FILTER_REJECT;
          }
          return NodeFilter.FILTER_ACCEPT;
        }
      });

    let curNode;
    while (curNode = walker.nextNode()) {
      replaceTextNode(curNode);
    }
  }

  function matchCase(text, replacement) {
    const isAllCaps = text.toUpperCase() === text;
    const isCapitalized = text.charAt(0).toUpperCase() === text.charAt(0) && text.slice(1).toLowerCase() === text.slice(1);
    const isAllLower = text.toLowerCase() === text;

    if (isAllCaps) {
      return replacement.toUpperCase();
    } else if (isCapitalized) {
      return replacement.charAt(0).toUpperCase() + replacement.slice(1).toLowerCase();
    } else if (isAllLower) {
      return replacement.toLowerCase();
    }

    return replacement;
  }

  const observer = new MutationObserver(mutations => {
    for (const mutation of mutations) {
      for (const node of mutation.addedNodes) {
        if (node?.nodeType === Node.TEXT_NODE) replaceTextNode(node);
        else if (node?.nodeType == Node.ELEMENT_NODE) replaceElementNode(node);
      }
    }
  });

  replaceElementNode(document.head.querySelector('title'));
  observer.observe(document.body, {
    childList: true,
    subtree: true
  });

  const origAttachShadow = Element.prototype.attachShadow;
  Element.prototype.attachShadow = function(init) {
    const shadow = origAttachShadow.call(this, init);
    observer.observe(shadow, {
      childList: true,
      subtree: true
    });
    return shadow;
  };
})();