firstWeekFirstDayInYear method

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

当年第一周的第一天。 算法：获取1月4号所在周的第一天

Implementation

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