JSFiddle - React, Tailwind, and code Playground

HTML

<div id="parent" class="foo">
  <div id="child">
  </div>
</div>

JavaScript

$(function(){
  var element = $('#parent').children('#child');
  if (element.is('.foo *')) {
    console.log('Yay!');
  } else {
    console.log('Duh!');
  }
});