How to Subtract Seconds From a Date in JavaScript

Tari Ibaba
Last updated on October 26, 2022
How to Subtract Seconds From a Date in JavaScript

Let's learn how to easily subtract any number of seconds from a Date object in JavaScript.

1. Date setSeconds() and getSeconds() methods

To subtract seconds from a Date:

  1. Call the getSeconds() method on the Date to get the number of seconds.
  2. Subtract the seconds.
  3. Pass the result of the subtraction to the setSeconds() method.

For example:

function subtractSeconds(date, seconds) {
  date.setSeconds(date.getSeconds() - seconds);

  return date;
}

// July 10, 2022 at 5:35:40 pm
const date = new Date('2022-07-10T17:35:40.000Z');

const newDate = subtractSeconds(date, 10);

// July 10, 2022 at 5:35:30 pm
console.log(newDate); // 2022-07-10T17:35:30.000Z

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

The Date getSeconds() method returns a number between 0 and 59 that represents the seconds of a particular Date.

The Date setSeconds() method sets the seconds of a Date to a specified number.

If the seconds subtracted decrease the minute, hour, day, month, or year of the Date object, setHours() automatically updates the Date information to reflect this.

// July 10, 2022 at 5:20:00 pm
const date = new Date('2022-07-10T17:20:00.000Z');

date.setSeconds(date.getSeconds() - 130);

// July 10, 2022 at 5:17:50 pm
console.log(date); // 2022-07-10T17:17:50.000Z

In this example, decreasing the seconds of the Date by 130 decreases the minutes by 3 and sets the seconds to 50.

Avoiding side effects

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

function subtractSeconds(date, seconds) {
  // make copy with Date() constructor
  const dateCopy = new Date(date);

  dateCopy.setSeconds(date.getSeconds() - seconds);

  return dateCopy;
}

// July 10, 2022 at 5:35:40 pm
const date = new Date('2022-07-10T17:35:40.000Z');

const newDate = subtractSeconds(date, 10);

// July 10, 2022 at 5:35:30 pm
console.log(newDate); // 2022-07-10T17:35:30.000Z

// original not modified
console.log(date); // 2022-07-10T17:35:40.000Z

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 subSeconds() function

Alternatively, we can use the subSeconds() function from the date-fns NPM package to quickly subtract seconds from a Date. It works similarly to our pure subtractSeconds() function.

import { subSeconds } from 'date-fns';

// July 10, 2022 at 5:35:40 pm
const date = new Date('2022-07-10T17:35:40.000Z');

const newDate = subSeconds(date, 10);

// July 10, 2022 at 5:35:30 pm
console.log(newDate); // 2022-07-10T17:35:30.000Z

// original not modified
console.log(date); // 2022-07-10T17:35:40.000Z
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