JSFiddle - React, Tailwind, and code Playground

HTML

<div id="element">Ein Element</div>

CSS

#element { height: 20px; background: red; }

JavaScript

(function () {
    
    window.onresize = setWidth;
    window.onload = setWidth;
    
    var element;
    
    function getWidth () {
        return (Math.random() * 500) + 50;
    }
    function setWidth () {
        if (!element) element = document.getElementById('element');
        element.style.width = getWidth() + 'px';
    }
    
    
})();