這一段是倒計時的代碼，他是什么意思？？function checkTime(i){    if(i<10)    {        i="0"+i;    }    return i;}var time = setInterval('showTime()',500);function showTime(){  　var timedate= new Date("2018/12/01,10:13:55");                  　　var now = new Date();                                         　　var date = parseInt(timedate.getTime() - now.getTime())/1000; 　  if(date <= 0)　  {　      document.getElementById("txtshow").innerHTML="倒計時已經結束";　      clearInterval(time);　  }　　var day = parseInt(date/60/60/24);         var hour = parseInt(date/60/60%24);    var minute = parseInt(date/60%60);    var second = parseInt(date%60);    hour = checkTime(hour);    minute = checkTime(minute);    second = checkTime(second);    var leftTime = day+"天"+hour+"時"+minute+"分"+second+"秒";    document.getElementById('timeShow').innerHTML = leftTime;    time;