title: Upgrading to react@18 and react-dom@18 fails
body: <p>I have an existing React 17 app that started life as a create-react-app output with the TypeScript option.  I wanted to change package.json to include <code>react@18.0.0</code> and <code>react-dom@18.0.0</code> and then start the app, and that step worked fine.</p>
  <p>Then I tried to change the <code>index.tsx</code> file the way that the React 18 migration instructions tell you to do it, by changing the relevant segment in <code>index.tsx</code> to:</p>
  <pre class="lang-js prettyprint-override"><code>ReactDOM.createRoot(
    &lt;React.StrictMode&gt;
      &lt;App /&gt;
    &lt;/React.StrictMode&gt;,
    document.getElementById('root')
  );
  </code></pre>
  <p>and either <code>npm run build</code> or <code>npm run start</code> gives me compile errors, saying that createRoot is not defined. This is probably due to the fact that I have dependencies on <code>@types/react@17.0.43</code> and <code>@types/react-dom@17.0.14</code>. There do not seem to be any updated versions of these files from DefinitelyTyped for React 18 yet.</p>
  <p>So, I went back and created a brand new app with <code>npx create-react-app react18 --template typescript</code>. It now wants <code>react@18</code> and <code>react-dom@18</code>, but still has the old <code>@types/</code> dependencies. It also gives the same compile error when you switch from render() to createRoot().</p>
  <p>As one further step, I asked myself &quot;what happens if we leave out TypeScript?&quot; Created yet another app with <code>npx create-react-app react18js</code>. It depends on <code>react@18.0.0</code> and <code>react-dom@18.0.0</code> as expected, but still generates <code>ReactDOM.render()</code> in its <code>index.js</code> output.</p>
  <p>That works, but change <code>ReactDOM.render</code> to <code>ReactDOM.createRoot</code> and you get no compile errors, but you also get no visible output if you try <code>npm run start</code>. It doesn't seem to render the <code>&lt;App/&gt;</code> component at all.</p>
  <p>Am I missing something? Are the instructions not quite adequate?</p>