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 t

Answer 1

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

Answer 2

Using moment.js:

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

Answer 3

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

Answer 4

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)

Answer 5

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.

Answer 6

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);