JavaScript 計算倒計時

/**
 * 計算倒計時
 * @param endtime('yyyy-mm-dd hh:mm:ss' 格式 或者 timestamp 格式)
 * @param 'yyyy-mm-dd hh:mm:ss' 格式 或者 timestamp 格式)
 * @return obj對象(obj.days（天）,obj.hours（時）,obj.minutes（分）,obj.seconds（秒）)
 */
function caculateCountDownTime(endtime,nowtime){
    var timeObj = new Object();
    var endtimeDate = new Date(endtime);
    var nowtimeDate = new Date(nowtime);
    var endtimeStamp;
    var nowtimeStamp;
    if(endtimeDate == "Invalid Date"){
        endtimeStamp = endtime;
    }else{
        endtimeStamp = endtimeDate.getTime();
    }
    if(nowtimeDate == "Invalid Date"){
        nowtimestamp = nowtime;
    }else{
        nowtimestamp = nowtimeDate.getTime();
    }
    if(endtimeStamp>nowtimestamp){
          var date3=endtimeStamp-nowtimestamp; //時間差的毫秒數
          //計算出相差天數
          var days=Math.floor(date3/(24*3600*1000))
          //計算出小時數
          var leave1=date3%(24*3600*1000)    //計算天數后剩余的毫秒數
          var hours=Math.floor(leave1/(3600*1000))
          //計算相差分鐘數
          var leave2=leave1%(3600*1000)        //計算小時數后剩余的毫秒數
          var minutes=Math.floor(leave2/(60*1000))
          //計算相差秒數
          var leave3=leave2%(60*1000)      //計算分鐘數后剩余的毫秒數
          var seconds=Math.round(leave3/1000)
          timeObj.days = days;
          timeObj.hours = hours;
          timeObj.minutes = minutes;
          timeObj.seconds = seconds;
      }else{
          timeObj.days = 0;
          timeObj.hours = 0;
          timeObj.minutes = 0;
          timeObj.seconds = 0;
      }
      return timeObj;
}