Launch an effect when element has specific class dynamically

I want to launch an alert when a specific element has certain class, but this class is only added by another trigger after the DOM is loaded. How can i capture the moment when this specific element recieve his new class and launch an other event?

Ex:

    <a class="active"></a>
    <a class="">&开发者_如何学Golt;/a>
    <a class=""></a>

    Click on <div>next</div>

    |
    V

   <a class=""></a>
   <a class="active"></a>
   <a class=""></a>

   Click on <div>next</div>

   |
   V
  <a class=""></a>
  <a class=""></a>
  <a class="active"></a> -> launch an alert at this moment

Thanks!!

---

There is no event raised by default when an element's class is changed. It is possible to raise an event manually though, like this:

$("#element").addClass("myClass");
$("#element").trigger("classChanged");

// Somewhere else in code:

$("#element").bind("classChanged", function() {
    // do something
});