Исходный код этого примера:

timestr = "00:00:00";
title=document.title;

tid = 0;
pause = 0;
var to;
var bcount;
var tcount;
function time(n) {
tid=window.setTimeout("time(1)",to);
today = new Date()
if(today.getMinutes() < 10) pad = "0"
else pad = "";
if(today.getSeconds() < 10) pads = "0"
else pads = "";
timestr=today.getHours()+":"+pad+today.getMinutes()+":"+pads+today.getSeconds();
document.title = title+' '+timestr;
window.clearTimeout(tid);
tid=window.setTimeout("time()",to);
}
function start(x) {
f=x;
to=60;
time(x);
}
function cleartids() {
window.clearTimeout(tid);
}