js倒计时

//倒计时
        function countdown(times, callback){
            var _this = this;
            var timer = null;
              timer=setInterval(function(){
                var day=0, hour=0, minute=0, second=0;//时间默认值
                if(times > 0){
                      day = Math.floor(times / (60 * 60 * 24));
                      hour = Math.floor(times / (60 * 60)) - (day * 24);
                      minute = Math.floor(times / 60) - (day * 24 * 60) - (hour * 60);
                      second = Math.floor(times) - (day * 24 * 60 * 60) - (hour * 60 * 60) - (minute * 60);
                }
                if (day <= 9) day = '0' + day;
                if (hour <= 9) hour = '0' + hour;
                if (minute <= 9) minute = '0' + minute;
                if (second <= 9) second = '0' + second;
                //console.log(minute+"分钟："+second+"秒");
                var new_time = day + '天' + hour + '小时' + minute + '分' + second + '秒';
                typeof callback == "function" ? callback({time: new_time}) : '';
                times--;
            },1000);
            if(times<=0){
                clearInterval(timer);
            }
        }