代码：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
</head>
<body onload="startTime()">
<script>
// var date = new Date();
// date.setFullYear(2010,1,11)
// document.write(date)
//时钟
function startTime() {
var today = new Date();
var h = today.getHours();
var m = today.getMinutes();
var s = today.getSeconds();
m = checkTime(m);
s = checkTime(s);
document.getElementById("timetxt").innerHTML = h+":"+m+":"+s
t= setTimeout(function () { //setTimeout的中的500的意思是多久调用一次函数，这里使用了递归
startTime()
},500);
}
function checkTime(i) {
if(i<10){
i = "0" + i;
}
return i
}
</script>
<div id="timetxt"></div>
</body>
</html>
利用setInterval()方法来实现
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
</head>
<body>
<p id="ptime"></p>
<script>
var mytime = setInterval(function () {
getTime();
},1000);
function getTime() {
var d = new Date();
var t = d.toLocaleTimeString();
document.getElementById("ptime").innerHTML = t;
}
</script>
</body>
</html>