function setWatch(){
var now = new Date();
var nowH = now.getHours();
var nowM = now.getMinutes();
var nowS = now.getSeconds();
if (nowH < 10) { nowH = "0" + nowH; }
if (nowM < 10) { nowM = "0" + nowM; }
if (nowS < 10) { nowS = "0" + nowS; }
now = nowH + ":" + nowM + ":" + nowS;
window.status = now;
setTimeout("setWatch()",1000);
}
<BODY onLoad="setWatch()">