JSFiddle - React, Tailwind, and code Playground

HTML

<div style="width:10px;border:0;margin:0;padding:0;">
    <div id="test" style="width:25%;border:0;margin:0;padding:0;">
    </div>
</div>

JavaScript

console.log(document.getElementById('test').getBoundingClientRect());
console.log(document.getElementById('test').getBoundingClientRect().width);
console.log(document.getElementById('test').offsetWidth);