setTimeout 与setInterval的区别
setTimeout(code,millisec) 方法用于在指定的毫秒数后调用函数或计算表达式
setInterval(code,millisec) 方法可按照指定的周期（以毫秒计）来调用函数或计算表达式
区别：setTimeout() 只执行 code 一次。如果要多次调用，请使用 setInterval() 或者让 code 自身再次调用 setTimeout()
setTimeout() 函数实现时钟的例子
DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>预备启动秒表title>
<script type="text/javascript">
function timedMsg()
{
var second = document.getElementById("second").value;
var minute = document.getElementById("minute").value;
var hour = document.getElementById("hour").value;
second = parseInt(second);
minute = parseInt(minute);
hour = parseInt(hour);
var second = second + 1;
if(second >59){
second = 0;
minute = minute + 1;
if(minute > 59){
minute = 0;
hour = hour + 1;
if(hour>23){
hour = 0;
}
}
}
//数据格式处理
if(second < 10){
second = "0" + second;
}
if(minute < 10){
minute = "0" + minute;
}
if(hour < 10){
hour = "0" + hour;
}
document.getElementById('second').value= second;
document.getElementById('minute').value= minute;
document.getElementById('hour').value= hour;
var t = setTimeout("timedMsg();",1000);
}
script>
head>
<body>
<button onclick="timedMsg()">预备启动秒表button>
<br>
<br>
时<input type="text" name="hour" id="hour" value="00">
分<input type="text" name="minute" id="minute" value="00">
秒<input type="text" name="second" id="second" value="00">
body>
html>