title: Simple GetElementById issue
body: <p>I'm new to javascript I'm having a very simple problem. I just don't get what's going on.</p>
  
  <p>I just want to add a class to a <code>&lt;div&gt;</code> tag but it's not working</p>
  
  <p>This is my javascript:</p>
  
  <pre><code>var element = document.getElementById("main");
  element.classList.add("hidden");
  </code></pre>
  
  <p>Here's my fiddle:</p>
  
  <p><a href="http://jsfiddle.net/72o6j6r0/" rel="nofollow">http://jsfiddle.net/72o6j6r0/</a></p>