How to find the nearest day of the week with date-fns

Question

I want to be able to find out the nearest Day of the week in the past based on the current date with date-fns. Say I need to find nearest Friday, Wednesday, Thursday etc in the past based on the current date.

I looked in to the documentation and can see only these tow methods https://date-fns.org/docs/closestTo and https://date-fns.org/v1.29.0/docs/getDay that I thought might help but the one I am looking for is missing.

Any thoughts?

Answer 1

// use require or import in your code
// const { getISODay, addDays } = require("date-fns");
const { getISODay, addDays } = dateFns;

function getDayInPast(dayOfWeek, fromDate = new Date()) {
  // follow the getISODay format (7 for Sunday, 1 for Monday)
  const dayOfWeekMap = {
    Mon: 1,
    Tue: 2,
    Wed: 3,
    Thur: 4,
    Fri: 5,
    Sat: 6,
    Sun: 7,
  };

  // dayOfWeekMap[dayOfWeek] get the ISODay for the desired dayOfWeek
  const targetISODay = dayOfWeekMap[dayOfWeek];
  const fromISODay = getISODay(fromDate);

  // targetISODay >= fromISODay means we need to trace back to last week
  // e.g. target is Wed(3), from is Tue(2)
  // hence, need to -7 the account for the offset of a week
  const offsetDays =
    targetISODay >= fromISODay
      ? -7 + (targetISODay - fromISODay)
      : targetISODay - fromISODay;

  return addDays(fromDate, offsetDays);
}

console.log(getDayInPast("Mon"));
console.log(getDayInPast("Tue"));
console.log(getDayInPast("Wed"));
console.log(getDayInPast("Thur"));
console.log(getDayInPast("Fri"));
console.log(getDayInPast("Sat"));
console.log(getDayInPast("Sun"));

<script src="https://cdnjs.cloudflare.com/ajax/libs/date-fns/1.30.1/date_fns.min.js"></script>

Thanks @giraff for pointing out the issue about offset in the previous version