Calculate previous working day excluding weekends and federal holidays in JavaScript

Question

I am writing a function which will provide me previous working day for any given date. Working day means it is a weekday and there's no federal holiday on that day.

My solution works when today (case 1) is '2019-06-20T07:00:00.000Z'; i.e. thursday // returns wed Also, works when today (case 2) is '2019-06-24T07:00:00.000Z' i.e. monday // returns friday

But fails when today (case 3) is 2019-05-28T07:00:00.000Z // tuesday.

For case 3, it should return previous business day as 24th May (Friday), Since Monday(27th May) is a holiday. It returns 27th May, Monday for case 3.

Below is my code, in my or statement I'm checking for previous day but it doesn't consider that,

const { DateTime } = require('luxon');// I'm using luxon for DateTime.
      function check_previous_business_date(date, timezone) {
      const startDate = new Date(DateTime.fromISO(date).setZone(timezone));
      const todayTimeStamp = +new Date(startDate); // Unix timestamp in milliseconds
      const oneDayTimeStamp = 1000 * 60 * 60 * 24; // Milliseconds in a day
      const diff = todayTimeStamp - oneDayTimeStamp;
      const yesterdayDate = new Date(diff);
      const yesterdayString = yesterdayDate.getFullYear()
         + '-' + (yesterdayDate.getMonth() + 1) + '-' + yesterdayDate.getDate();
      for (startDate.setDate(startDate.getDate() - 1);
        !startDate.getDay() || startDate.getDay() === 6 ||
        federalHolidays.includes(startDate.toISOString().split('T')[0]) ||
        federalHolidays.includes(yesterdayString);
        startDate.setDate(startDate.getDate() - 1)
      ) { 
      }

      return startDate.toISOString().split('T')[0];
    }


 const federalHolidays= [
  '2019-5-27',
  '2019-09-02',
  '2019-10-14',
  '2019-11-11',
  '2019-11-28',
  '2019-12-25',
  '2020-01-01',
  '2020-01-20',
  '2020-02-17',
  '2020-05-25',
  '2020-07-03',
  '2020-09-07',
  '2020-10-12',
  '2020-11-11',
  '2020-11-26',
  '2020-12-25',
  '2021-01-01',
  '2021-01-18',
  '2021-02-15',
  '2021-05-31',
  '2021-07-05',
  '2021-09-06',
  '2021-10-11',
  '2021-11-11',
  '2021-11-25',
  '2021-12-24',
  '2021-12-31',
  '2022-01-17',
  '2022-02-21',
  '2022-05-30',
  '2022-07-04',
  '2022-09-05',
  '2022-10-10',
  '2022-11-11',
  '2022-11-24',
  '2022-12-26',
  '2023-01-02',
  '2023-01-16',
  '2023-02-20',
  '2023-05-29',
  '2023-07-04',
  '2023-09-04',
  '2023-10-09',
  '2023-11-10',
  '2023-11-23',
  '2023-12-25',
  '2024-01-01',
  '2024-01-15',
  '2024-02-19',
  '2024-05-27',
  '2024-07-04',
  '2024-09-02',
  '2024-10-14',
  '2024-11-11',
  '2024-11-28',
  '2024-12-25',
  '2025-01-01',
  '2025-01-20',
  '2025-02-17',
  '2025-05-26',
  '2025-07-04',
  '2025-09-01',
  '2025-10-13',
  '2025-11-11',
  '2025-11-27',
  '2025-12-25',
  '2026-01-01',
  '2026-01-19',
  '2026-02-16',
  '2026-05-25',
  '2026-07-03',
  '2026-09-07',
  '2026-10-12',
  '2026-11-11',
  '2026-11-26',
  '2026-12-25',
  '2027-01-01',
  '2027-01-18',
  '2027-02-15',
  '2027-05-31',
  '2027-07-05',
  '2027-09-06',
  '2027-10-11',
  '2027-11-11',
  '2027-11-25',
  '2027-12-24',
  '2027-12-31',
  '2028-01-17',
  '2028-02-21',
  '2028-05-29',
  '2028-07-04',
  '2028-09-04',
  '2028-10-09',
  '2028-11-10',
  '2028-11-23',
  '2028-12-25',
  '2029-01-01',
  '2029-01-15',
  '2029-02-19',
  '2029-05-28',
  '2029-07-04',
  '2029-09-03',
  '2029-10-08',
  '2029-11-12',
  '2029-11-22',
  '2029-12-25'
];
    check_previous_business_date('2019-05-28T07:00:00.000Z', 'America/New_York');

// <script //src="https://cdn.jsdelivr.net/npm/luxon@1.21.1/build/global/luxon.min.j//s"></script>

Answer 1

You are not using Luxon to its full potential. You should leave the date as a Luxon object, do all the operations on it using Luxon's methods, and then convert the date into a string.

To do that, I defined a helper function prevBusinessDayHelper that takes a Luxon datetime and returns a date time representing the previous business day. It operates entirely in terms of Luxon datetimes, which makes it easy. Then in the outer function, I convert to and from Luxon datetimes.

const DateTime = luxon.DateTime;

// use a Set to make lookups cheaper
const federalHolidays = new Set([
  '2019-05-27', // <-- you were missing the 0 here in yours
  '2019-09-02',
  // snip
]);

// recursion is good here because it's very shallow
const prevBusinessDayHelper = dt => {

  // use luxon's tools!
  const yest = dt.minus({ days: 1 });

  if (yest.weekday == 6 || yest.weekday == 7 || federalHolidays.has(yest.toISODate()))
    return prevBusinessDayHelper(yest);

  return yest;
};

const prevBusinessDay = (isoString, zone) => {
  const dt = DateTime.fromISO(isoString).setZone(zone);
  return prevBusinessDayHelper(dt).toISODate();
};

console.log(prevBusinessDay("2019-05-28T07:00:00.000Z", "America/New_York"));

<script src="https://cdn.jsdelivr.net/npm/luxon@1.21.1/build/global/luxon.min.js"></script>

Answer 2

When you are checking for holidays array you are checking full date instead of the date part.

function check_previous_business_date(date, timezone) {
      const startDate = new Date(luxon.DateTime.fromISO(date).setZone(timezone));
      const todayTimeStamp = +new Date(startDate); // Unix timestamp in milliseconds
      const oneDayTimeStamp = 1000 * 60 * 60 * 24; // Milliseconds in a day
      const diff = todayTimeStamp - oneDayTimeStamp;
      const yesterdayDate = new Date(diff);
      const yesterdayString = yesterdayDate.getFullYear()
         + '-' + (yesterdayDate.getMonth() + 1) + '-' + yesterdayDate.getDate();
      for (startDate.setDate(startDate.getDate() - 1);
        !startDate.getDay() || startDate.getDay() === 6 ||
        federalHolidays.includes(startDate.toISOString().split('T')[0]) ||
        federalHolidays.includes(yesterdayString);
        startDate.setDate(startDate.getDate() - 1)
      ) { 
      }

      return startDate.toISOString().split('T')[0];
    }
const federalHolidays= [
  '2019-05-27',
  '2019-09-02',
  '2019-10-14',
  '2019-11-11'
];
console.log('Prev. day of 2019-05-28 is ',check_previous_business_date('2019-05-28T07:00:00.000Z', 'America/New_York'));
console.log('Prev. day of 2019-06-20 is ',check_previous_business_date('2019-06-20T07:00:00.000Z', 'America/New_York'));

<script src="https://cdn.jsdelivr.net/npm/luxon@1.21.1/build/global/luxon.min.js"></script>