https://www.kvasiny.cz/bundles/datumcas/js/datumcas.js?v=v6.5.0b

1function SetDate(objDate) {
2    var hours = objDate.getHours();
3    var minutes = objDate.getMinutes();
4    var seconds = objDate.getSeconds();
5
6    if (hours == 0) hours = '0' + hours;
7    if (minutes <= 9) minutes = '0' + minutes;
8    if (seconds <= 9) seconds = '0' + seconds;
9
10    var field = document.getElementById('datumcas');
11    if (field) field.innerHTML = hours + ':' + minutes + ':' + seconds;
12}
13
14function Clock() {
15    var currentDate = new Date();
16    SetDate(currentDate);
17    setTimeout('Clock()', 1000);
18}
19function InitClock() {
20    Clock();
21}
22evt.add(window, 'load', InitClock);