Beginner Exercism • javascript

Meetup

Challenge Overview

Your task is to find the exact date of a meetup, given a month, year, weekday and week.

Introduction

Every month, your partner meets up with their best friend. Both of them have very busy schedules, making it challenging to find a suitable date! Given your own busy schedule, your partner always double-checks potential meetup dates with you:

“Can I meet up on the first Friday of next month?”
“What about the third Wednesday?”
“Maybe the last Sunday?”

In this month’s call, your partner asked you this question:

“I’d like to meet up on the teenth Thursday; is that okay?”

Confused, you ask what a “teenth” day is. Your partner explains that a teenth day, a concept they made up, refers to the days in a month that end in ‘-teenth’:

13th (thirteenth)
14th (fourteenth)
15th (fifteenth)
16th (sixteenth)
17th (seventeenth)
18th (eighteenth)
19th (nineteenth)

As there are also seven weekdays, it is guaranteed that each day of the week has exactly one teenth day each month.

Now that you understand the concept of a teenth day, you check your calendar. You don’t have anything planned on the teenth Thursday, so you happily confirm the date with your partner.

Instructions

Your task is to find the exact date of a meetup, given a month, year, weekday and week.

There are six week values to consider: first, second, third, fourth, last, teenth.

For example, you might be asked to find the date for the meetup on the first Monday in January 2018 (January 1, 2018).

Similarly, you might be asked to find:

the third Tuesday of August 2019 (August 20, 2019)
the teenth Wednesday of May 2020 (May 13, 2020)
the fourth Sunday of July 2021 (July 25, 2021)
the last Thursday of November 2022 (November 24, 2022)
the teenth Saturday of August 1953 (August 15, 1953)

Teenth

The teenth week refers to the seven days in a month that end in ‘-teenth’ (13th, 14th, 15th, 16th, 17th, 18th and 19th).

If asked to find the teenth Saturday of August, 1953, we check its calendar:

    August 1953
Su Mo Tu We Th Fr Sa
                   1
 2  3  4  5  6  7  8
 9 10 11 12 13 14 15
16 17 18 19 20 21 22
23 24 25 26 27 28 29
30 31

From this we find that the teenth Saturday is August 15, 1953.

Source: Exercism javascript/meetup

💡 View Solution

const WEEKDAYS = ['Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday'];

export const meetup = (year, month, week, day) => {
  const dayIndex = WEEKDAYS.indexOf(day);
  let startDay = 1;
  let endDay = new Date(year, month, 0).getDate();

  if (week === 'teenth') {
    startDay = 13;
    endDay = 19;
  } else if (week === 'first') {
    startDay = 1;
    endDay = 7;
  } else if (week === 'second') {
    startDay = 8;
    endDay = 14;
  } else if (week === 'third') {
    startDay = 15;
    endDay = 21;
  } else if (week === 'fourth') {
    startDay = 22;
    endDay = 28;
  } else if (week === 'last') {
    startDay = endDay - 6;
  }

  for (let d = startDay; d <= endDay; d++) {
    const date = new Date(year, month - 1, d);
    if (date.getDay() === dayIndex) return date;
  }
};