例子，setTimeout实现一个简单的计时器。
推荐：javascript计时器工作原理
<!DOCTYPE html>
<html>
<head>
<script>
var c=0;
var t;
var timer_is_on=0;
//js计时器代码
function timedCount()
{
document.getElementById('txt').value=c;
c=c+1;
t=setTimeout("timedCount()",1000);
}
function doTimer()
{
if (!timer_is_on)
{
timer_is_on=1;
timedCount();
}
}
</script>
</head>
<body>
<form>
<input type="button" value="Start count!" onClick="doTimer()">
<input type="text" id="txt">
</form>
<p>Click on the button above. The input field will count forever, starting at 0.</p>
</body>
</html>