How to get the index of the ACTIVE CHILD div of my container with jQuery?

<div id="container">
  <div class="active">
      <div class="active"></div>
  </div>
  <div>
  <开发者_StackOverflow/div>
</div>

How to write such a container?

Use .index() without parameters to get it's (0-based) index amongst siblings, like this:

var index = $("#container .active").index();

You can test it out here. For your example markup, it would be 0.