title: Javascript: Loop Through every third child node
body: <p>If I got a parent node, how can I loop through every third child node?</p>
  
  <p>I've got now this code:</p>
  
  <pre><code>var parents = document.getElementById('ID_of_parent');
  var first_child = parents.firstChild.data.id;
  alert(parents);
  alert(first_child);
  </code></pre>
  
  <p>For the parents, i got now '<em>[object HTMLDivElement]</em>' and for first_child i got '<em>undefined</em>'.</p>