How to Subtract Years From a Date in JavaScript

1. Date setFullYear() and getFullYear() methods

To subtract years from a Date in JavaScript:

1. Call the getFullYear() method on the Date to get the year.
2. Subtract the years.
3. Pass the result of the subtraction to the setFullYear() method.

For example:

function subtractYears(date, years) {
  date.setFullYear(date.getFullYear() - years);
  return date;
}

// Feb 20, 2022
const date = new Date('2022-02-20T00:00:00.000Z');

const newDate = subtractYears(date, 3);

// Feb 20, 2019
console.log(newDate); // 2019-02-20T00:00:00.000Z

Our subtractYears() function takes a Date object and the number of years to subtract as arguments. It returns the same Date object with the years subtracted.

The Date getFullYear() method returns a number that represents the year of a particular Date.

The Date setFullYear() method sets the year of a Date to a specified number.

Avoid side effects

The setFullYear() method mutates the Date object it is called on. This introduces a side effect into our subtractYears() function. To avoid modifying the passed Date and create a pure function, make a copy of the Date and call setFullYear() on this copy, instead of the original.

function subtractYears(date, years) {
  // 👇 make copy with "Date" constructor
  const dateCopy = new Date(date);

  dateCopy.setFullYear(date.getFullYear() - years);

  return dateCopy;
}

const date = new Date('2022-02-20T00:00:00.000Z');

const newDate = subtractYears(date, 3);

// Feb 20, 2019
console.log(newDate); // 2019-02-20T00:00:00.000Z

// 👇 Original not modified
console.log(date); // 2022-02-20T00:00:00.000Z

Tip: Functions that don’t modify external state (i.e., pure functions) tend to be more predictable and easier to reason about, as they always give the same output for a particular input. This makes it a good practice to limit the number of side effects in your code.

2. date-fns subYears() function

Alternatively, we can use the subYears() function from the date-fns NPM package to quickly subtract years from a Date. It works like our pure subtractYears() function.

import { subYears } from 'date-fns';

const date = new Date('2022-02-20T00:00:00.000Z');

const newDate = subYears(date, 3);

// Feb 20, 2019
console.log(newDate); // 2019-02-20T00:00:00.000Z

// 👇 Original not modified
console.log(date); // 2022-02-20T00:00:00.000Z

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