live clock javascript

1//javascript
2var span = document.getElementById('clock');
3
4function time() {
5  var d = new Date();
6  var s = d.getSeconds();
7  var m = d.getMinutes();
8  var h = d.getHours();
9  span.textContent = 
10    ("0" + h).substr(-2) + ":" + ("0" + m).substr(-2) + ":" + ("0" + s).substr(-2);
11}
12
13setInterval(time, 1000);
14
15//html
16<span id="clock"></span>