基于jquery的-获取短信验证码-倒计时

1 <input class="gain" type="button" value="获取验证码">

 1 var istime=true;
 2     $(".gain").click(function(){if(istime){getCode($(this),30)}})
 3 
 4     //获取验证码
 5     function getCode(a,n){//a:DOM节点,n:倒数秒数
 6         istime=false;
 7         a.val(n+"s");
 8         var times=setTimeout(changetime,1000);
 9         function changetime(){
10             if(n>0){n--;a.val(n+"s");times=setTimeout(changetime,1000);}else{clearTimeout(times);a.val("重新获取");istime=true;}
11         }
12     }