Get Monday date of the upcoming week

Question

I'm trying to get the date of Monday of the upcoming week, so for example, if I run the script now I will get 2021-09-13.

I tried solving this myself, and wrote this:

export function getMondayDate() {
  const d = new Date();
  const DAYS_IN_WEEK = 7;

  var today = d.getDay()


  const daysToMonday = (DAYS_IN_WEEK - today) + 1;
  const Monday = d.getDate() + d.getDay() + daysToMonday;

  return new Date(d.setDate(Monday));
}

I thought about getting the current day, so for example getDay() will return 3.

So, when subtracting DAYS_IN_WEEK from today, will result in the number 4 that would get Sunday and than to add 1 to get Monday. So, from Today, it will be 5 days to get to Monday.

But for some reason I get the wrong date, I can't really see what's wrong here.

What do you expect when today is Sunday? Tomorrow? Or 8 days later? — trincot, Sep 08 '21 at 19:04
Does this answer your question? [Get next week's date of a certain day in JavaScript](https://stackoverflow.com/questions/43582087/get-next-weeks-date-of-a-certain-day-in-javascript) — jsejcksn, Sep 08 '21 at 19:22

trincot · Accepted Answer · 2021-09-08T19:14:03.437

2

You shouldn't add d.getDay() to d.getDate(). You have already used d.getDate() to determine daysToMonday, so you should not use it again.

Secondly, if you want on a Sunday to get the next day as return value (instead of one week later), then you should add a % 7 in the formula.

Currently your function will return a date with a time part that is equal to the current time. Maybe you want to reset the time part to 0.

function getMondayDate() {
  const d = new Date();
  const daysToMonday = (7 - d.getDay()) % 7 + 1;
  const monday = d.getDate() + daysToMonday;

  return new Date(d.getFullYear(), d.getMonth(), monday);
}

console.log(getMondayDate().toString());

edited Sep 08 '21 at 19:14

answered Sep 08 '21 at 19:08

trincot

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was going to close it as duplicate :) https://stackoverflow.com/a/43582700/17447 – naveen Sep 08 '21 at 19:19
While the JS Date constructor attempts to correct invalid day of month values (e.g. potential overflows like in your code example), is it wise to rely on that behavior? – jsejcksn Sep 08 '21 at 19:21
@jsejcksn, this behaviour is baked into the [ECMAScript language specification](https://tc39.es/ecma262/multipage/numbers-and-dates.html#sec-date-constructor). We can rely on it. – trincot Sep 08 '21 at 19:33

choz · Answer 2 · 2021-09-08T19:37:53.883

You can use Date.prototype.getDay to get the day in the week. From there, you have enough information to get when's the next monday.

E.g.

const nowMs = Date.now();
const today = new Date(nowMs);

/*
The getDay() method returns the day of the week for the specified date according to local time, where 0 represents Sunday
*/
const dayOfTheWeek = today.getDay();

// Monday is 1st day of the week, so..
const itsSunday = dayOfTheWeek === 0;
let deltaDayToMonday;

if (itsSunday) {
  deltaDayToMonday = 1; // monday is tomorrow
}
else {
  deltaDayToMonday = 8 - dayOfTheWeek;
}

console.log(`Monday is in ${deltaDayToMonday} day(s)`);

/*
We're using the milliseconds to generate the new date for monday
To handle the dates overflowing months or years
*/
const nextMondayInMs = nowMs + (deltaDayToMonday * 24 * 60 * 60 * 1000);
const nextMondayUtc = new Date(nextMondayInMs);

console.log("Next monday is", nextMondayUtc.toLocaleString());

Get Monday date of the upcoming week

2 Answers2