定时器1：setTimeout()
<!DOCTYPE html>
<html>
<head>
<title>js12.html</title>
<script type="text/javascript">
function count()
{
setTimeout("alert('执行成功')",2000); //两秒钟后执行 alert
}
</script>
</head>
<body>
<input type = "button" value = "计时开始" name = "timing" onclick="count()">
</body>
</html>
第二种：setInterval()
<!DOCTYPE html>
<html>
<head>
<title>js13.html</title>
<script type="text/javascript">
var sec = 0;
var timeId = setInterval("count();", 1000);//每隔 1 秒执行一次 count()
function count()
{
document.getElementById("num").innerHTML = sec++;
}
function stop()
{
clearInterval(timeId);
}
</script>
</head>
<body>
<font color="red" id ="num">0</font>秒钟
<input type = "button" value = "停止" onclick="stop();" >
</body>
</html>
结果： 点击 Stop，计时停止