arrays - Javascript - How do i get every date in a week from a given week number and year

Question

How do I get every weekday (monday through friday) in a week from a given week number

input

var weekNumber = "week + " " + year"; //"35 2020"

Wanted output

var weekArray = ["2020-08-24", "2020-08-25", "2020-08-26", "2020-08-27", "2020-08-28"];

Answer 1

Here's an example building on top of: javascript calculate date from week number

Get the first date of the week, then return an array of 7 elements, incrementing the date for each element.

If the day number goes above the number of days in the month, then add one to the month temp.m and reset the day temp.d equal to one.

function getISOWeek(w, y) {
    var simple = new Date(y, 0, 1 + (w - 1) * 7);
    var dow = simple.getDay();
    var ISOweekStart = simple;
    if (dow <= 4)
        ISOweekStart.setDate(simple.getDate() - simple.getDay() + 1);
    else
        ISOweekStart.setDate(simple.getDate() + 8 - simple.getDay());
    const temp = {
      d: ISOweekStart.getDate(),
      m: ISOweekStart.getMonth(),
      y: ISOweekStart.getFullYear(),
    }
    //console.log(ISOweekStart)
    const numDaysInMonth = new Date(temp.y, temp.m + 1, 0).getDate()
    
    return Array.from({length: 7}, _ => {
      if (temp.d > numDaysInMonth){
        temp.m +=1;
        temp.d = 1;
        // not needed, Date(2020, 12, 1) == Date(2021, 0, 1)
        /*if (temp.m >= 12){
          temp.m = 0
          temp.y +=1
        }*/
      }      
      return new Date(temp.y, temp.m, temp.d++).toUTCString()
    });
}

// var weekNumber = "week + " " + year"; //"35 2020"
const weekNumber = "53 2020";

const weekYearArr = weekNumber.split(" ").map(n => parseInt(n))

const weekOut = getISOWeek(...weekYearArr) 

console.log(weekOut);