Custom util to get weekday name or number

const getDayNameOrNo = (value) => {
  const mappings = [
    [0, "sunday"],
    [1, "monday"],
    [2, "tuesday"],
    [3, "wednesday"],
    [4, "thursday"],
    [5, "friday"],
    [6, "saturday"],
  ];

  const match = mappings.find(
    ([dayNo, name]) => dayNo === value || name === value
  );

  if (!match) return;

  const [matchedNo, matchedName] = match;
  return matchedNo === value ? matchedName : matchedNo;
};

console.log(getDayNameOrNo(0)); // sunday
console.log(getDayNameOrNo("sunday")); // 0
console.log(getDayNameOrNo("friday")); // 5

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Comments

[Ste Griffiths]

Thanks for the post. I think you could improve it by removing the hardcoded English day names and using the JS built-in features to get the day of the week in your locale.

Typescript:

getWeekDays(locale): string[] {
    var baseDate = new Date(Date.UTC(2017, 0, 1)); // just a Sunday
    var weekDays = [];
    for (let i = 0; i < 7; i++) {
      let dayName = baseDate.toLocaleDateString(locale, { weekday: 'long' });
      dayName = dayName[0].toUpperCase() + dayName.slice(1);
      weekDays.push(dayName);
      baseDate.setDate(baseDate.getDate() + 1);
    }
    return weekDays;
  }

[Mehul Lakhanpal]

Great i did not know that. Thanks 😀