JSFiddle - React, Tailwind, and code Playground

HTML

<div></div>

CSS

div {
  height: 100px;
  margin: 50px 0;
  
  display: block;
  width: 100px;
  background: tomato;
}

JavaScript

var el = document.querySelector('div');

var elHeight = el.offsetHeight;
elHeight += parseInt(window.getComputedStyle(el).getPropertyValue('margin-top'));
elHeight += parseInt(window.getComputedStyle(el).getPropertyValue('margin-bottom'));

console.log(elHeight);