JSFiddle - React, Tailwind, and code Playground

HTML

<div id="test">This is a test.</div>

CSS

#test
{
    background-color: red;
    width: 100px;
}

JavaScript

var elem=document.getElementById('test');
if(window.getComputedStyle)
{
    // Modern browsers
    alert('Our width is: ' + window.getComputedStyle(test).width);
}
else if(elem.currentStyle)
{
    // IE8 and below
    alert('Our width is: ' + elem.currentStyle.width);
}