title: After changing parentNode.innerHTML, can't access parentNode
body: <p>Say I have the following DOM structure and scripts</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>var test = document.getElementById('test');
  test.parentNode.innerHTML += 'hello';
  console.log(test.parentNode); // null
  console.log(document.getElementById('test').parentNode); // normal result</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;div&gt;
  &lt;div id="test"&gt;&lt;/div&gt;
  &lt;/div&gt;</code></pre>
  </div>
  </div>
  </p>
  
  <p>As above script says, the first outputs <code>null</code> while the second outputs the actual node, does anyone know why the first output <code>null</code> rather than the normal node?</p>