js 简单实现获取短信按钮倒计时60秒

<!DOCTYPE html>
<html lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>js实现倒计时60秒的简单代码(推荐)</title>
<script type="text/javascript" src="js/jquery.js"></script>
</head>

<body>
<input type="button" id="btn" value="免费获取验证码" onclick="settime(this)" />
<script type="text/javascript">
var countdown=60;
function settime(val) {
if (countdown == 0) {
val.removeAttribute("disabled");
val.value="免费获取验证码";
countdown = 60;
} else {
val.setAttribute("disabled", true);
val.value="重新发送(" + countdown + ")";
countdown--;
setTimeout(function() {
settime(val)
},1000)
}

}
</script>
</body>
</html>