//獲得某月的最后一天 
        function getLastDay(year,month) {        
             var new_year = year;    //取當前的年份         
             var new_month = month++;//取下一個月的第一天，方便計算（最后一天不固定）         
             if(month>12) {        
              new_month -=12;        //月份減         
              new_year++;            //年份增         
             }        
             var new_date = new Date(new_year,new_month,1);                //取當年當月中的第一天         
             return (new Date(new_date.getTime()-1000*60*60*24)).getDate();//獲取當月最后一天日期         
        }