title: Uncaught TypeError: Cannot read property 'clientHeight' of null
body: <p>I don't know why it can't find the height. Any help would be appreciated.</p>
  
  <pre><code>var h = document.getElementById('big_button').clientHeight,
      center = -h / 2;
  window.onload = function () {
      document.getElementById('big_button_container2').style.marginTop = 'center';
  };
  </code></pre>
  
  <p><a href="http://jsfiddle.net/4zux6/" rel="nofollow">http://jsfiddle.net/4zux6/</a></p>