JSFiddle - React, Tailwind, and code Playground

JavaScript

var body = $$('body')[0];

var test = new Element('div', {'style':'visibility:hidden; width: 100px; height: 100px; overflow: scroll;'});

test.inject(body);

var scrollbar = {
    width: test.offsetWidth - test.scrollWidth
    , height: test.offsetHeight - test.scrollHeight
}

test.set('text',  [test.offsetWidth, test.scrollWidth, scrollbar.width, scrollbar.height].join(',') );

test.setStyle('visibility', '');