title: Uncaught TypeError: Cannot set property 'className' of undefined
body: <p>When you reduce the browser window a separate layout has been put for iPhone screens;
  you can see two arrows and when you click the right arrow it will move to the next slider, but I am not able to see the cubes.
  When I looked in close I see one error:</p>
  <blockquote>
  <p>Uncaught TypeError: Cannot set property 'className' of undefined</p>
  </blockquote>
  <p><a href="http://jsfiddle.net/UL3R2/" rel="nofollow noreferrer">http://jsfiddle.net/UL3R2/</a></p>
  <pre><code> var slider = new Swipe(document.getElementById('slider'), {
              callback: function(e, pos) {
  
                  var i = bullets.length;
                  while (i--) {
                      bullets[i].className = ' ';
                  }
                  bullets[pos].className = 'on';
  Uncaught TypeError: Cannot set property 'className' of undefined
  
              }
          }),
  </code></pre>