JSFiddle - React, Tailwind, and code Playground

HTML

<div id="relogio"></div>

JavaScript

function relogio(id) {
    var target = document.querySelector(id);
    function pad(nr) {
        return nr < 10 ? '0' + nr : nr;
    }
    return function() {
        var rel = new Date();
        var hora = rel.getHours();
        var minuto = rel.getMinutes();
        var segundo = rel.getSeconds();
        target.innerText = [hora, minuto, segundo].map(pad).join(':');
    }
}
window.setInterval(relogio('#relogio'), 1000);