JSFiddle - React, Tailwind, and code Playground

HTML

<div id="computed">This div has width and height set in CSS.</div>

CSS

#computed{
    width: 14em;
    height: 14em;
    background: rgba(00,00,00,.3);
}

JavaScript

$('#computed').click(function(){
    alert($(this).css('width') + "\n" + $(this).width());
});