title: Error "reactRouter is undefined" when using script from CDN
body: <p>I am trying to use ReactRouterDOM in a plain-vanilla HTML + JSX page, using a CDN to retrieve the various React dependencies, as shown in the code below.</p>
  <p>When the JSX code ...</p>
  <pre><code>        &lt;BrowserRouter&gt;
            &lt;Routes&gt;
              &lt;Route path=&quot;/&quot; element={&lt;Home /&gt;} /&gt;
            &lt;/Routes&gt;
          &lt;/BrowserRouter&gt;
  </code></pre>
  <p>... is used, the browser complains that <code>React.useRef is not a function</code>. Do I need to use a different version of the CDN scripts, or is there one that I am missing?</p>
  <hr />
  <pre><code>&lt;!DOCTYPE html&gt;
  &lt;html&gt;
    &lt;head&gt;
  
      &lt;script src=&quot;https://cdnjs.cloudflare.com/ajax/libs/react/16.6.3/umd/react.development.js&quot;&gt;&lt;/script&gt;
      &lt;script src=&quot;https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.6.3/umd/react-dom.development.js&quot;&gt;&lt;/script&gt;  
      &lt;script src=&quot;https://cdnjs.cloudflare.com/ajax/libs/react-router/6.3.0/react-router.development.js&quot;&gt;&lt;/script&gt;    
      &lt;script src=&quot;https://cdnjs.cloudflare.com/ajax/libs/react-router-dom/6.3.0/react-router-dom.development.js&quot;&gt;&lt;/script&gt;
      &lt;script src=&quot;https://cdnjs.cloudflare.com/ajax/libs/babel-core/5.8.23/browser.js&quot;&gt;&lt;/script&gt;
  
      &lt;title&gt;React Router by CDN&lt;/title&gt;
    &lt;/head&gt;
  &lt;body&gt;
    &lt;div id=&quot;root&quot;&gt;&lt;/div&gt;
  
    &lt;script type=&quot;text/babel&quot;&gt;
      const {
        BrowserRouter,
        Routes,
        Route
      } = ReactRouterDOM
  
  
      function App() {
        return &lt;Home /&gt;
        // Comment out the line above to create an error that says
        // Uncaught TypeError: React.useRef is not a function
        
        return (
          &lt;BrowserRouter&gt;
            &lt;Routes&gt;
              &lt;Route path=&quot;/&quot; element={&lt;Home /&gt;} /&gt;
            &lt;/Routes&gt;
          &lt;/BrowserRouter&gt;
        );
      }
  
  
      function Home() {
        return (&lt;div&gt;
          This is Home
        &lt;/div&gt;)
      }
  
  
      ReactDOM.render(
        &lt;App /&gt;,
        document.getElementById(&quot;root&quot;)
      )
    &lt;/script&gt;
  &lt;/body&gt;
  &lt;/html&gt;
  </code></pre>