<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title></title>
</head>
<body>
<form>
<input type="button" value="開始計時！" onClick="timedCount()">
<input type="text" id="txt">
</form>
<p>請點擊上面的按鈕。輸入框會從 0 開始一直進行計時。</p>
<script>
var c=0
var t
function timedCount()
{
document.getElementById('txt').value=c
c=c+1
t=setTimeout("timedCount()",1000)
}
</script>
</body>
</html>