JSFiddle - React, Tailwind, and code Playground
HTML
<div id="container" style="border: 1px solid; height: 100px; width: 500px;"></div>
JavaScript
var height = document.getElementById('container').style.height;
alert(height);
<div id="container" style="border: 1px solid; height: 100px; width: 500px;"></div>
var height = document.getElementById('container').style.height;
alert(height);