How to implement countdown in JS

function countDown(times){
    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 = &#39;0&#39; + day;
        if (hour <= 9) hour = &#39;0&#39; + hour;
        if (minute <= 9) minute = &#39;0&#39; + minute;
        if (second <= 9) second = &#39;0&#39; + second;
        //
        console.log(day+"天:"+hour+"小时："+minute+"分钟："+second+"秒");
        times--;
    },1000);
    if(times<=0){
        clearInterval(timer);
    }
}//单纯分钟和秒倒计时
function resetTime(time){
    var timer=null;
    var t=time;
    var m=0;
    var s=0;
    m=Math.floor(t/60%60);
    m<10&&(m=&#39;0&#39;+m);
    s=Math.floor(t%60);
    function countDown(){
      s--;
      s<10&&(s=&#39;0&#39;+s);
      if(s.length>=3){
        s=59;
        m="0"+(Number(m)-1);
      }
      if(m.length>=3){
        m=&#39;00&#39;;
        s=&#39;00&#39;;
        clearInterval(timer);
      }
      console.log(m+"分钟"+s+"秒");
    }
    timer=setInterval(countDown,1000);
}