<!DOCTYPE html>
<html>
<head>
<script src="http://libs.baidu.com/jquery/1.10.2/jquery.min.js"></script>
<script type="text/javascript">
var countdown=60;
function settime(obj) {
if (countdown == 0) {
obj.removeAttribute("disabled");
obj.value="免费获取验证码";
countdown = 60;
return;
} else {
obj.setAttribute("disabled", true);
obj.value="重新发送(" + countdown + ")";
countdown--;
}
setTimeout(function() {
settime(obj)
},1000)
}
</script>
<body>
<input type="button" id="btn" value="免费获取验证码" onclick="settime(this)" />
</body>
</html>
原文：http://www.cnblogs.com/clphp/p/5909301.html