Give element class when specific element has active class

Question

Is it possible with Jquery to add another class to the .body element when the third li element has an .active class? It cant just add an class based on the .active class, it has to be the .active on the third li element specifically.

<div id="extendedinfobox">
   <ul class="prodtabmenu">
    <li></li>
    <li></li>
    <li class="active"></li>
    <li></li>
    <li></li>
  </ul>
 </div>
<div class="body">

Answer 1

https://jsfiddle.net/sn2nc9bd/1/

if($('ul.prodtabmenu').find('li:nth-child(3)').hasClass('active'))
{
   $('.body').addClass('newClass');   
}

Answer 2

if ($('ul.prodtabmenu').find('li:nth-child(3)').hasClass('active')) {
  //$('body').addClass('disabled');
  $('.body').addClass('disabled');
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.0/jquery.min.js"></script>
<div id="extendedinfobox">
  <ul class="prodtabmenu">
    <li>2</li>
    <li>21</li>
    <li class="active">3</li>
    <li>4</li>
    <li>1</li>
  </ul>
</div>
<div class="body">

Try like this

Use .nth-child()

Description: Selects all elements that are the nth-child of their parent.

use .nth-child(3) to select the 3rd li