Is there a more efficient method for subtracting a set number of months from a date without having to repeat code?

Question

Is there a more efficient method for subtracting a set number of months from a date without having to repeat code?

Trying to develop a function that takes the current date as input using:

    const currDate = new Date()

The goal is to pass this value to a function that subtracts a specific number of months from the current date and returns the result in RFC 3399 format.

Referenced a post here, which provided a function for date subtraction:

export function subtractMonths(numOfMonths: number, date: Date = new Date()) {
  date.setMonth(date.getMonth() - numOfMonths);

  return date;
}

Encountering an issue when calling the function and formatting it. It changes the date instead of retaining the original value:

      const currDate = new Date(); // "2022-08-24T18:26:33.965Z"
      const endDate = subtractMonths(6, currDate) // this alters currDate to "2022-02-24T19:26:33.965Z"
      
      const formattedStartDate = endDate.toISOString() // "2022-08-24T18:26:33.965Z"
      const formattedEndDate = currDate.toISOString() // "2022-08-24T18:26:33.965Z"

Currently resolving the issue by creating two instances of the Date object, but seeking a more efficient approach to achieve this task.

Edit: Acknowledging the need to duplicate the date objects. Looking for a cleaner method to write the function while maintaining functionality.

javascript typescript datetime

Answer 1

Answer №1

Your function is currently mutating the date parameter, causing it not to work as expected. To fix this issue, you should clone the parameter so that only the clone is mutated.

Here is an updated version of your function:

export function subtractMonths(numOfMonths: number, date: Date = new Date()) {
  const clonedDate = new Date(date);
  clonedDate.setMonth(date.getMonth() - numOfMonths);

  return clonedDate;
}

If you need to manipulate dates and have the option to use external libraries, I recommend using date-fns

Answer 2

Your function is currently mutating the date parameter, causing it not to work as expected. To fix this issue, you should clone the parameter so that only the clone is mutated.

Here is an updated version of your function:

export function subtractMonths(numOfMonths: number, date: Date = new Date()) {
  const clonedDate = new Date(date);
  clonedDate.setMonth(date.getMonth() - numOfMonths);

  return clonedDate;
}

If you need to manipulate dates and have the option to use external libraries, I recommend using date-fns

Answer 3

Answer №2

I have a similar approach for determining if a given date falls on the last day of the month. This involves creating a new instance of Date since modifying the existing object using .setMonth() would change the original date. The same concept applies to .setDate() as demonstrated in the code snippet below.

function checkLastDayOfMonth(inputDate) {
    var tempDate = new Date(inputDate),
        day = tempDate.getDate();
    tempDate.setDate(day + 1);
    return tempDate.getMonth() !== inputDate.getMonth();
}

Answer 4

I have a similar approach for determining if a given date falls on the last day of the month. This involves creating a new instance of Date since modifying the existing object using .setMonth() would change the original date. The same concept applies to .setDate() as demonstrated in the code snippet below.

function checkLastDayOfMonth(inputDate) {
    var tempDate = new Date(inputDate),
        day = tempDate.getDate();
    tempDate.setDate(day + 1);
    return tempDate.getMonth() !== inputDate.getMonth();
}

Is there a more efficient method for subtracting a set number of months from a date without having to repeat code?

Answer №1

Answer №2

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