JSFiddle - React, Tailwind, and code Playground

HTML

<div id="progress"></div>
<div id="runs"></div>

CSS

#progress {
    width: 0%;
    background-color: #cfc;
    height: 30px;
    padding: 5px;
}

JavaScript

var progress = document.getElementById('progress');
var runLogger = document.getElementById('runs');
var runs = 0;
var comeco = new Date().getTime();
var periodical = setInterval(function () {
    var start = new Date().getTime();
    for (var i = 0; i < 1000; i++) {
        for (var x = 0; x < 101; x++) {
            progress.innerHTML = x;
            progress.style.width = x + '%';
        }
    }

    var end = new Date().getTime();
    runLogger.innerHTML = ['Run nr: ' + runs, 'Dur. individual esperada: ' + 500, 'Dur. individual: ' + (end - start), '    Dur.total: ' + (end - comeco), 'Dur. total esperada: ' + (runs * 500)].join('<br />');
    if (runs++ > 9) clearInterval(periodical);
}, 500);