https://mrcoles.com/bookmarklet/

React Bookmarklet.js

function loadScript(url) {
  return new Promise(function (resolve, reject) {
    try {
      function callback() {
        resolve(url);
      }
      var s = document.createElement("script");
      s.src = url;
      if (s.addEventListener) {
        s.addEventListener("load", callback, false);
      } else if (s.readyState) {
        s.onreadystatechange = callback;
      }
      document.body.appendChild(s);
    } catch (e) {
      reject(e);
    }
  });
}

(async function () {
  const loadReact = await loadScript(
    "https://unpkg.com/react@16/umd/react.development.js"
  );
  const loadReactDOM = await loadScript(
    "https://unpkg.com/react-dom@16/umd/react-dom.development.js"
  );
  console.log("React loaded", React);
  window.React = React;
})();