JSFiddle - React, Tailwind, and code Playground

HTML

<div id="hiddenParent">
  <div class="childDiv">child div 1</div>
  <div class="childDiv">child div 2</div>
  <div class="childDiv">child div 3</div>
</div>

CSS

.childDiv{
  height:10px;
}

JavaScript

var height = $(".childDiv").height();
$("#hiddenParent").hide();
alert(height);