倒计时定时器

function invokeSettime(obj){//发送验证码倒计时
            var countdown=60;
            settime(obj);
            function settime(obj) {
              if (countdown == 0) {
                $(obj).attr("disabled",false);
                $(obj).text("获取短信验证码");
                countdown = 60;
                return;
             } else {
                $(obj).attr("disabled",true);
                $(obj).text("(" + countdown + ") s 重新发送");
                countdown--;
             }
            setTimeout(function() {
                    settime(obj) }
                ,1000)
          }
     }