计算是今年的第几天

/**
 * @param:  '2014,4,1'或  Date对象
 */
function getWhichDay(time){ 
     var datetime = new Date(),
	     gap = 0;
		 
	  if(time){
		datetime = time instanceof Date ? time : new Date(time);
		gap = 1;
	  } 

     var day_MillSeconds=24*3600*1000, //一天的秒数
         year = datetime.getFullYear(),
         firstDay = new Date(year, 0, 1);    //新年第一天
 
     var dayOfYear = (datetime-firstDay) / day_MillSeconds +  gap;
     return Math.ceil(dayOfYear);
 }