title: Access a React component method / state from outside the component
body: <p>I have embedded a <code>reactjs</code> component into an existing HTML page by referencing it's ID like described in React's tutorial:</p>
  
  <pre><code>ReactDOM.render(
    &lt;Page /&gt;,
    document.getElementById('my-react-compnent')
  );
  </code></pre>
  
  <p>Then:</p>
  
  <pre><code>&lt;div id="my-react-compnent&gt;&lt;/div&gt;
  </code></pre>
  
  <p>The component is displayed and works as expected.</p>
  
  <p>Now I want to link a button located on that page to my component (to be specific I would like to retrive its state, but for the example even invoking one of its methods would be fine).</p>
  
  <p>In other words - when clicking the outside button, I want to invoke a method from the <code>Page</code> component?</p>
  
  <p>How can I do that?</p>