setInterval()

js/script.js

function funClock() {
var date = new Date();
var hours = date.getHours();
var minutes = date.getMinutes();
var seconds = date.getSeconds();
if(hours < 10) {
hours = '0' + hours;
}
if(minutes < 10) {
minutes = '0' + minutes;
}
if(seconds < 10) {
seconds = '0' + seconds;
}
var time = hours + ':' + minutes + ':' + seconds;
document.getElementById('t').innerHTML = time;
}
function funMake() {
setInterval('funClock()', 1000);
}

function funClock() {
var date = new Date();
var hours = date.getHours();
var minutes = date.getMinutes();
var seconds = date.getSeconds();
if(hours < 10) {
hours = '0' + hours;
}
if(minutes < 10) {
minutes = '0' + minutes;
}
if(seconds < 10) {
seconds = '0' + seconds;
}
var time = hours + ':' + minutes + ':' + seconds;
document.getElementById('t').innerHTML = time;
}
function funMake() {
setInterval('funClock()', 1000);
}

index.html

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title>New Page</title>
<script src="js/script.js"></script>
</head>
<body>
<time id="t"></time>
<script>
funMake();
</script>
</body>
</html>

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title>New Page</title>
<script src="js/script.js"></script>
</head>
<body>
<time id="t"></time>
<script>
funMake();
</script>
</body>
</html>