八百年一次，这个七月有5个礼拜五，5个礼拜六，5个礼拜天（js Date对象练习良好方案）[原]

     < script >
         // move back one month
         function  prevMonth(thisMonth, thisYear) {
             if  (thisMonth  ==   1 ) {
                thisM  =   12 ;
                thisY  =  (thisYear  -   1 );
            }
             else  {
                thisM  =  (thisMonth  -   1 );
                thisY  =  thisYear;
            }
        }

         // move forward one month
         function  nextMonth(thisMonth, thisYear) {
             if  (thisMonth  ==   12 ) {
                thisM  =   1 ;
                thisY  =  (thisYear  +   1 )
            }
             else  {
                thisM  =  (thisMonth  +   1 );
                thisY  =  thisYear;
            }
        }
         // 转化为短的日期格式
         function  toShortDate(date) {
             var  dateStr  =  date.getFullYear()  +   " - "   +  (date.getMonth()  +   1 )  +   " - "   +  date.getDate();
             return  dateStr;
        }

         var  dtNow  =   new  Date();
         var  thisM  =  dtNow.getMonth() + 1 ;
         var  thisY  =  dtNow.getFullYear();
         var  arrayRecord  =  [];
         while  (thisY  >=   1900 ) {
            prevMonth(thisM, thisY);
             var  lastDayOfPrevMonth  =   new  Date(thisY, thisM,  0 );
             if  (lastDayOfPrevMonth.getDay()  ==   0   &&  lastDayOfPrevMonth.getDate()  ==   31 ) {
                arrayRecord.push(toShortDate(lastDayOfPrevMonth));
            }
        }

        document.write(arrayRecord.join( " \r " ));
     < / script>