title: How to add a callback for setAttribute?
body: <p>Is it possible to add a callback on <code>setAttribute</code> on Prototype ? </p>
  
  <p>For this example, I would like to show an <code>alert("done !")</code> when <code>setAttribute()</code> is finished. </p>
  
  <pre><code>img.setAttribute("src", "http://blabla.com/c.jpg");
  </code></pre>