javascript把毫秒转换为小时/分钟/秒的格式

今天遇到需要计算一个距离开场时间相差了多少时间的需求：

var date = new Date(),
	year = date.getFullYear(),
	month = date.getMonth() + 1,
	day = date.getDate(),
	hours = date.getHours(),
	minutes = date.getMinutes(),
	seconds = date.getSeconds();

month = month<10?'0'+month:month;
day = day<10?'0'+day:day;
hours = hours<10?'0'+hours:hours;
minutes = minutes<10?'0'+minutes:minutes;
seconds = seconds<10?'0'+seconds:seconds;

var startTime = new Date(year + '/' + month + '/' + day + '/' + ' 09:00:00'); //开始时间戳
var endTime = new Date().getTime() - startTime.getTime();  //当前时间减去开始时间相差毫秒数
alert(MillisecondToDate(endTime));//输出转换成时间格式

function MillisecondToDate(msd) {
   var time = parseFloat(msd) / 1000;
   if (null != time && "" != time) {
      if (time > 60 && time < 60 * 60) {
         time = getzf(parseInt(time / 60.0)) + ":" + getzf(parseInt((parseFloat(time / 60.0)) -
                  getzf(parseInt(time / 60.0)) * 60)) + "";
      }
      else if (time >= 60 * 60 && time < 60 * 60 * 24) {
         time = getzf((parseInt(time / 3600.0))) + ":" + getzf(parseInt((parseFloat(time / 3600.0) -
               parseInt(time / 3600.0)) * 60)) + ":" +
            getzf(parseInt((parseFloat((parseFloat(time / 3600.0) - parseInt(time / 3600.0)) * 60) -
               parseInt((parseFloat(time / 3600.0) - parseInt(time / 3600.0)) * 60)) * 60)) + "";
      }
      else {
         time = parseInt(time) + "";
      }
   }
   return time;
}
//补零
function getzf(num){
   if(parseInt(num) < 10){
      num = '0'+num;
   }
   return num;
}