JSFiddle - React, Tailwind, and code Playground

HTML

<div id="time" data-now="1429018329000"></div>

JavaScript

var elem  = document.getElementById('time');
var timer = setInterval(initTime, 1000);

function initTime() {
    var time = +(elem.getAttribute('data-now')),
    time = time + 1000; // add one second
        
    var today = new Date( time ),
        h = today.getHours(),
        m = today.getMinutes(),
        s = today.getSeconds();

        m = checkTime(m);
        s = checkTime(s);
    
    elem.innerHTML = h + ":" + m + ":" + s;
    elem.setAttribute('data-now', today.getTime());
}

function checkTime(i) {
    if (i < 10) {
        i = "0" + i
    }; // add zero in front of numbers < 10
    return i;
}