I’m trying to find week days between first date and second date (exclusive first and second). In the array that contains the weekday dates, the values get increment after line 1 in executed, which is unexpected.

private getListOfWeekDaysBetweenTwoDates(
    startDate: Date,
    endDate: Date
  ): Date[] {
    const weekdaysList = [];
    let tempDate = this.addDaystoGivenDate(startDate, 1);
    while (tempDate < endDate) {
      if (this.isWeekDay(tempDate)) {
        weekdaysList.push(tempDate);
      }
//line 1
      tempDate = this.addDaystoGivenDate(tempDate, 1);
    }
    return weekdaysList;
  }

 private addDaystoGivenDate(date: Date, numberOfDays: number): Date {
    return new Date(date.setUTCDate(date.getUTCDate() + numberOfDays));
  }

private isWeekDay(day: Date): boolean {
    if (day.getUTCDay() >= 1 && day.getUTCDay() <= 5) {
      return true;
    }
    return false;
  }

How do I stop array values changing?

>Solution :

Isolating the problem, you’re changing the date after inserting it to the array, but what you’re inserting is a reference to the date:

let d = new Date()
d.setUTCDate(1)
const arr = []
arr.push(d)
console.log(arr)
d.setUTCDate(10)
console.log(arr) //date in arr changes from 1 to 10

That’s because you’re calling date.setUTCDate() over tempDate.

There is more than one way to solve it, but for example you could store not the reference to tempDate but a completely new Date object:

weekdaysList.push(tempDate); => weekdaysList.push(new Date(tempDate));

In the simplified example:

let d = new Date()
const arr = []
d.setUTCDate(1)
arr.push(new Date(d))
console.log(arr)
d.setUTCDate(10)
console.log(arr) //date in arr keeps 1