firstWeekLastDayInYear method

DateTime firstWeekLastDayInYear([
  1. int firstWeekDay = 1
])

当年第一周的最后一天。 算法：获取1月4号所在的周

Implementation

DateTime firstWeekLastDayInYear([int firstWeekDay = 1]) {
  return DateTime(year, 1, 4).lastDayInWeek(firstWeekDay);
}