Testing react bug with dev libraries not working in tampermonkey environment.

test-react.user.js

// ==UserScript==
// @name         Test react bug with dev module
// @version      0.1
// @description  React Development
// @author       Prozacgod
// @match        http://localhost:8080/
// @grant       unsafeWindow
// @grant      GM_registerMenuCommand
// @grant      GM_xmlhttpRequest

// Works with these
// @require       https://cdnjs.cloudflare.com/ajax/libs/react/16.4.2/umd/react.development.js
// @require       https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.4.2/umd/react-dom.development.js

// // @require    https://cdnjs.cloudflare.com/ajax/libs/react/16.10.2/umd/react.production.min.js
// // @require    https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.10.2/umd/react-dom.production.min.js

// Crashes/Infinite loops in different ways with 16.5.2 and onward (development versions)
// // @require       https://cdnjs.cloudflare.com/ajax/libs/react/16.10.2/umd/react.development.js
// // @require       https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.10.2/umd/react-dom.development.js

// ==/UserScript==

(function() {
    'use strict';

    let elem = document.getElementById('testing-element');
    if (!elem) {
        elem = document.createElement('div');
        elem.id = 'testing-element';
        document.body.appendChild(elem);
    }

    ReactDOM.render(React.createElement('div', {}, ["Foo!"]), elem);
})();