JavaScript for getting the previous Monday

Question

I would like for the previous Monday to appear in the field where a user enters today's date.

E.g.: If today's date is entered 29-Jan-16 then the code would make the previous Monday's date to appear instead (which would be 25-Jan-16).

I have seen some code online:

function getPreviousMonday() {
  var date = new Date();
  if (date.getDay() != 0) {
    return new Date().setDate(date.getDate() - 7 - 6);
  } else {
    return new Date().setDate(date.getDate() - date.getDate() - 6);
  }
}

However, this is not quite working, why?

Possible duplicate of [Javascript: get Monday and Sunday of the previous week](http://stackoverflow.com/questions/13681702/javascript-get-monday-and-sunday-of-the-previous-week) — Noel, Jan 29 '16 at 16:25
Or a dup of [get the first day of the week from current date](https://stackoverflow.com/questions/4156434/javascript-get-the-first-day-of-the-week-from-current-date) — James Gentes, Nov 07 '18 at 16:02

score 46 · Answer 1 · answered Oct 03 '17 at 12:19

46

var prevMonday = new Date();
prevMonday.setDate(prevMonday.getDate() - (prevMonday.getDay() + 6) % 7);

I am a little late but I like this solution. It's a one liner and not that complicated. Making a function for that seems overkill to me.

answered Oct 03 '17 at 12:19

Philippe Dubé-Tremblay

461
1
4
6

Thanks @Philippe for your nice solution. I've put a wrapping function which accepts a date here https://stackoverflow.com/a/52750444/2012407 for those who are interested – antoni Oct 11 '18 at 00:28
This works as following: add 6 days to `getDay()` (current day of the week, e.g. Friday=5) and the remainder of the division by the number of a week's days (`(5+6)%7=4`) is subtracted from the current's day number (e.g. `29-4=25`). – CPHPython Jan 30 '20 at 14:26

score 14 · Accepted Answer · edited Nov 07 '20 at 04:08

14

I think your math is just a little off, and I tidied your syntax;

function getPreviousMonday()
{
    var date = new Date();
    var day = date.getDay();
    var prevMonday = new Date();
    if(date.getDay() == 0){
        prevMonday.setDate(date.getDate() - 7);
    }
    else{
        prevMonday.setDate(date.getDate() - (day-1));
    }

    return prevMonday;
}

That way you always get the last Monday that happened (which is 7 days ago if today is Monday)

edited Nov 07 '20 at 04:08

Sagodi97

106
1
6

answered Jan 29 '16 at 15:38

Matthew Lymer

916
6
10

1

This returned a number for me instead of a date – PhoenixB Apr 24 '18 at 20:22
This returns the time since epoch (i believe), instead instantiate the new date object and then make changes. Trying to do it fluidly will not produce the result you are expecting. (Which is a Date object, instead you receive an integer back) – Ryan Rentfro Sep 02 '18 at 08:15
2

execute `new Date(prevMonday);` it will return date – ABHISHEK BHARDWAJ Aug 23 '19 at 05:58
date.getDay() returns Sunday for 0, not Monday... I like @Philippe Dubé-Tremblay's answer below. – Matt Fiocca Aug 19 '20 at 21:35

gfrobenius · Answer 3 · 2016-01-29T15:55:44.330

Here is a fiddle demonstrating a few different formats: https://jsfiddle.net/umefez2j/3/

function getMonday(d) {
  var m_names = new Array("Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec");
  var d = new Date(d);
  var day = d.getDay(),
      diff = d.getDate() - day + (day == 0 ? -6:1); // adjust when day is sunday

  //Use this one to return this format: Mon Jan 25 2016 09:37:51 GMT-0600 (Central Standard Time)
  //return new Date(d.setDate(diff));

  //Use this one to return this format: Mon, 25 Jan 2016
  //monday=new Date(d.setDate(diff)).toUTCString();
  //monday=monday.split(' ').slice(0, 4).join(' ')
  //return monday;

  //Use this one to return this format: 25-Jan-2016
  monday=new Date(d.setDate(diff));
  var curr_date = monday.getDate();
  var curr_month = monday.getMonth();
  var curr_year = monday.getFullYear();
  return curr_date + "-" + m_names[curr_month] + "-" + curr_year;
}

alert(getMonday(new Date()));

//Created with help from:
//http://stackoverflow.com/a/27480352/3112803
//http://stackoverflow.com/a/4156516/3112803
//http://stackoverflow.com/a/27869948/3112803

I edited the answer to include a third format and to give props to the source that helped generate this. Hope this helps. I see you're new to stackoverflow, if this works for you mark this as the answer please. — gfrobenius, Jan 29 '16 at 15:56

Nagaraj Raveendran · Answer 4 · 2020-01-30T11:50:27.467

1

Using moment.js:

moment().day("Monday").format('YYYY-MM-DD');

edited Jan 30 '20 at 11:50

answered Jan 30 '20 at 11:42

Nagaraj Raveendran

965
13
23

If today is Sunday `2020-05-10`, and shouldn't this give `2020-05-11` whereas the expected is, `2020-05-03` – tezz May 06 '20 at 10:45

antoni · Answer 5 · 2020-07-05T03:23:32.283

0

Thank you @Philippe Dubé-Tremblay for your nice solution (above),

I will just put here the wrapping function for those who, like me, plan to call this function repeatedly.

// Accepts a date as parameter or with no parameter will assume the current date.
const getPreviousMonday = (date = null) => {
  const prevMonday = date && new Date(date.valueOf()) || new Date()
  prevMonday.setDate(prevMonday.getDate() - (prevMonday.getDay() + 6) % 7)
  return prevMonday
}

edited Jul 05 '20 at 03:23

answered Oct 11 '18 at 00:23

antoni

3,652
25
37

Thanks, just small feedback: instead of rather us _const prevMonday_ instead of _let_ (just to avoid linters flashing :)) – Braulio Jul 04 '20 at 10:03
Thanks for your idea @Braulio, I updated the answer :) – antoni Jul 05 '20 at 03:24

Matt Fiocca · Answer 6 · 2020-08-20T22:01:04.553

0

Based on @Philippe Dubé-Tremblay answer, i wanted to come up with something that lets you target any previous day:

let target = 1 // Monday
let date = new Date()
date.setDate(date.getDate() - ( date.getDay() == target ? 7 : (date.getDay() + (7 - target)) % 7 ))

This takes into account the previous Monday if today is also Monday

edited Aug 20 '20 at 22:01

answered Aug 19 '20 at 21:47

Matt Fiocca

1,293
10
18

My solution gets the current date if we are monday. So if you want the same maths, replacing the hardcoded 6 by (7-target) should do it. If you want the last monday in that case, I think those maths work : date.setDate(date.getDate() - (date.getDay() + (6 - target) % 7 + 1) – Philippe Dubé-Tremblay Aug 20 '20 at 18:17
@Philippe Dubé-Tremblay, nice and simple, however if i try your update, it grabs two weeks ago, instead of this week. Example: if I target 2 (Tuesday) while running this today on a Thursday, your code grabs two Tuesdays ago instead of the Tuesday from the start of this week – Matt Fiocca Aug 20 '20 at 21:58
Parenthesis problem I think: date.setDate(date.getDate() - (date.getDay() + 6 - target) % 7 + 1) – Philippe Dubé-Tremblay Aug 21 '20 at 22:09

score -1 · Answer 7 · answered Feb 11 '18 at 03:24

The easiest solution is to go back the number of days based on today's date. For example, if today's day(0) is Sunday, you can go back 6 days to find the previous Monday. If Today is Monday, you can go back 7 days. Therefore using a modulo will help you in this scenario simply because the number of days you will need to go back is %7 plus 6. Let me break it down in simple steps.

var today=new Date();

This will give you today's date. Now,

var todaysDay=today.getDay();

This will give you your day starting with zero.

var goBack=today.getDay()%7+6;

Now, declare a new date.

var lastMonday=new Date().setDate(today.getDate()-goBack);

Now, this will give you a numeric date value. Convert it back to Date

var desiredDate=new Date(lastMonday);

This is not correct - if today is Wednesday(3) then you would do `(3 % 7) + 6 = 9`. You do not need to go back 9 days, but instead 2 days. The correct formula is `(3 + 6) % 7 = 2`. I.E. `goBack = (today.getDay() + 6) % 7` — Andrew McOlash, Mar 11 '18 at 20:29

JavaScript for getting the previous Monday

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