JSFiddle - React, Tailwind, and code Playground

HTML

<div id="testitem">
</div>
<div id="width">
</div>

CSS

#testitem {
  height: 200px;
}

JavaScript

var sizeImage = document.getElementById('testitem');
var sizeVue = sizeImage.offsetWidth +"x"+ sizeImage.offsetHeight;

document.getElementById('width').innerHTML = sizeVue;