How to index number of specific DIV simple html dom

Question

how would i get index number of div class="age" using simple html dom?

         <div class="main">   
          <div id="names">
             <div class="name">...</div>
             <div class="subject">...</div>
             <div class="class">...</div>
             <div class="age">...</div>
            </div>
      </div>

Answer 1

var parent = document.getElementById('names');
var c = parent.children;

for (var i=0; i< c.length; i++) 
  if (c[i].classList.contains('age'))
    console.log('Found at index '+ i);

<div class="main">
  <div id="names">
    <div class="name">...</div>
    <div class="subject">...</div>
    <div class="class">...</div>
    <div class="age">...</div>
  </div>
</div>