发送验证码 重发倒计时

//发送验证码 重发倒计时
var countdown=60; 
function settime(obj) { 
    if (countdown == 0) { 
        obj.removeAttribute("disabled");    
        obj.value="发送验证码"; 
        countdown = 60; 
        return;
    } else { 
        obj.setAttribute("disabled", true); 
        obj.value="重发(" + countdown + ")"; 
        countdown--; 
    } 
setTimeout(function() { 
    settime(obj) }
    ,1000) 
}