js实现点击获取验证码倒计时效果

<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<input type="button" style="height:32px;width:120px;" value="点击发送验证码" onclick="sendCode(this)" />
<script type="text/javascript">
 var clock = '';
 var nums = 10;
 var btn;
 function sendCode(thisBtn)
 { 
 btn = thisBtn;
 btn.disabled = true; //将按钮置为不可点击
 btn.value = nums+'秒后可重新获取';
 clock = setInterval(doLoop, 1000); //一秒执行一次
 }
 function doLoop()
 {
 nums--;
 if(nums > 0){
 btn.value = nums+'秒后可重新获取';
 }else{
 clearInterval(clock); //清除js定时器
 btn.disabled = false;
 btn.value = '点击发送验证码';
 nums = 10; //重置时间
 }
 }
</script>