get localWeekday() {
    return this.isValid ? possiblyCachedLocalWeekData(this).weekday : NaN;
  }
Get the day of the week according to the locale.
1 is the first day of the week and 7 is the last day of the week.
If the locale assigns Sunday as the first day of the week, then a date which is a Sunday will return 1,
@returns {number}