How to Get the First Day of the Current Week and Month

const today = new Date(); 
const firstWeekD = today.getDate() - today.getDay()-1; 
const lastWeekD = firstWeekD + 6; 
const firstdayOfWeek = new Date(today.setDate(firstWeekD)).toLocaleString("sv-SE").slice(0,10);
const lastdayOfWeek = new Date(today.setDate(lastWeekD)).toLocaleString("sv-SE").slice(0,10);
const date = new Date();
const firstDayOfMonth = new Date(date.getFullYear(), date.getMonth(), 1).toLocaleString("sv-SE").slice(0,10);
const lastDayOfMonth = new Date(date.getFullYear(), date.getMonth() + 1, 0).toLocaleString("sv-SE").slice(0,10);
  
console.log(firstdayOfWeek); // first day of the week - Saturday
console.log(lastdayOfWeek); // last day of the week - Friday
console.log(firstDayOfMonth) // first day of the month
console.log(lastDayOfMonth) // last day of the month

How to get the first, second, third, and fourth week of the month?

Below method return next weekday's DateTime what you want from now or specific day.

DateTime getNextWeekDay(int weekDay, {DateTime from}) {
  DateTime now = DateTime.now();

  if (from != null) {
    now = from;
  }

  int remainDays = weekDay - now.weekday + 7;

  return now.add(Duration(days: remainDays));
}

The weekday parameter can be came like below DateTime const value or just int value.

class DateTime {
...
  static const int monday = 1;
  static const int tuesday = 2;
  static const int wednesday = 3;
  static const int thursday = 4;
  static const int friday = 5;
  static const int saturday = 6;
  static const int sunday = 7;
...
}

If you want to get next Monday from now, call like below.

DateTime nextMonday = getNextWeekDay(DateTime.monday);

If you want to get next next Monday from now, call like below.

Or you just add 7 days to 'nextMonday' variable.

DateTime nextMonday = getNextWeekDay(DateTime.monday);


DateTime nextNextMonday = getNextWeekDay(DateTime.monday, from: nextMonday);
or
DateTime nextNextMonday = nextMonday.add(Duration(days: 7));

Get the first day of all weeks of current month in iOS swift

You can create a DateComponents with the components:

year: someYear,
month: someMonth,
weekday: someCalendar.firstWeekday,
weekOfMonth: n

use Calendar.date(from:) to get the Date corresponding to those components. Now you just need to vary n from 1 to 5, and put each result into an array.

var firstsOfWeek = [Date]()
let year = 2020
let month = 10
let calendar = Calendar.current

for n in 1...5 {
    let dc = DateComponents(
        year: year,
        month: month,
        weekday: calendar.firstWeekday,
        weekOfMonth: n
    )
    firstsOfWeek.append(calendar.date(from: dc)!)
}

However, date(from:) will return a date that is not in someMonth if the first week of someMonth is only partially inside someMonth. For example, (assuming the week starts on a Sunday) the first week of October 2020 starts on 27 September, and date(from:) will give you that date if you ask it what the date corresponding to weekOfMonth: 1 is.

If you don't want that date. simply add a check to only include the start of month if it is a start of week as well, and change the for loop range to 2...5:

let firstDayOfMonth = calendar.date(from: DateComponents(year: year, month: month))!
if calendar.component(.weekday, from: firstDayOfMonth) == calendar.firstWeekday {
    firstsOfWeek.append(firstDayOfMonth)
}
for n in 2...5 {
...

But do note that if you do this, the resulting array will sometimes have 4 elements, and sometimes 5 elements.

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