title: Changing a Main Image when clicking on thumbnail
body: <p>I have been trying this for a while now and have reached the point where I am missing something very simple but just cannot see it now, so any help would be appreciated!
  I have 2 thumbnails with id "one" and "two" and I would like to use them to change the main img on the page.</p>
  
  <pre><code>&lt;script type="text/javascript"&gt;
              //&lt;![CDATA[ 
                  window.onload= function(){
                  var mainImg= document.getElementByID('ci');
  
                  document.getElementByID('one').onclick= function(){
                  mainImg.src='burningbush.png';
                  //alert('one clicked');
                  };
                  document.getElementByID('two').onclick = function(){
                  mainImg.src='burningbush.png';
                  //alert('two clicked');
                  }
                  };//]]&gt;
  &lt;/script&gt;
  
  
  &lt;div id="mainContainer"&gt;
                      &lt;div id="image"&gt;
                          &lt;img src="images/home.jpg" id="ci" alt="" /&gt;
                      &lt;/div&gt;
                      &lt;div id="thumbnail"&gt;
                          &lt;img id="one" src="burningbush.png"&lt;/img&gt;
                          &lt;img id="two" src="burningbush.png"&lt;/img&gt;
                      &lt;/div&gt;
  
                  &lt;/div&gt;
  </code></pre>