Add weekdays to date

JavaScript, Date · Jan 7, 2021

Calculates the date after adding the given number of business days.

Use Array.from() to construct an array with length equal to the count of business days to be added.
Use Array.prototype.reduce() to iterate over the array, starting from startDate and incrementing, using Date.prototype.getDate() and Date.prototype.setDate().
If the current date is on a weekend, update it again by adding either one day or two days to make it a weekday.
NOTE: Does not take official holidays into account.

const addWeekDays = (startDate, count) =>
  Array.from({ length: count }).reduce(date => {
    date = new Date(date.setDate(date.getDate() + 1));
    if (date.getDay() % 6 === 0)
      date = new Date(date.setDate(date.getDate() + (date.getDay() / 6 + 1)));
    return date;
  }, startDate);

addWeekDays(new Date('Oct 09, 2020'), 5); // 'Oct 16, 2020'
addWeekDays(new Date('Oct 12, 2020'), 5); // 'Oct 19, 2020'

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