Пример пользовательского скрипта с React

React-Userscript.user.js

// ==UserScript==
// @name         React Userscript
// @namespace    http://tampermonkey.net/
// @version      0.1
// @description  shows how to use babel compiler
// @author       You
// @require      https://cdnjs.cloudflare.com/ajax/libs/babel-standalone/6.18.2/babel.js
// @require      https://cdnjs.cloudflare.com/ajax/libs/babel-polyfill/6.16.0/polyfill.js
// @require      https://unpkg.com/react@16/umd/react.development.js
// @require      https://unpkg.com/react-dom@16/umd/react-dom.development.js
// @require      https://ifx.su/~va
// @match        https://vk.com/*
// @noframes
// ==/UserScript==

var inline_src = (<><![CDATA[
class App extends React.Component {
  constructor(props) {
    super(props);
    this.state = {};
  }

  static searchElement(elements) {
    elements.forEach((el) => {
      if (!el || !el.querySelector) {
        return;
      }

      const action_search = el.querySelector('.im-action_search:not(.im-action_stat)');

      if (!action_search) {
        return;
      }

      const action_stat = action_search.cloneNode();

      action_stat.textContent = 'Test menu';
      action_stat.classNames += ' im-action_stat';
      action_stat.onclick = App.onMenuClick;

      action_search.parentElement.insertBefore(action_stat, action_search);
    })
  }

  static initSearch() {
    App.searchElement([document.body]);
    new MutationObserver((mutations) => {
      App.searchElement(mutations);
    }).observe(document.body, {
      subtree: true,
      childList: true,
    });
  }

  static onMenuClick() {
    alert('OK');
  }

  render() {
    return (
      <div> Hello React UserScript! </div>
    );
  }
}

App.initSearch();
]]></>).toString();

var source = Babel.transform(inline_src, { presets: [ "es2015", "es2016", "react" ] });
eval(source.code);