发送验证码

输入手机号，发送验证码 60s倒计时

   //验证码 倒计时
   var countdown=60;  
   function settime(item) {  
       if (countdown == 0) {  
           item.removeAttr("disabled");  
           item.val("获取验证码");  
           countdown = 60;  
           return false;  
       } else {  
           item.attr("disabled", true);  
           item.val("重新发送(" + countdown + ")");  
           countdown--;  
       }  
       setTimeout(function() {  
           settime(item);  
       },1000);  
   } 

<input value="获取验证码" readonly />