JavaScript - subtract hours from date

In this article, we would like to show you how to subtract hours from date in JavaScript.

Quick solution:

// ONLINE-RUNNER:browser;

const date = new Date('2021-06-30T00:00:00.000Z');

date.setHours(date.getHours() - 2);   // subtracted 2 hours from existing date

console.log(date.toISOString());      // 2021-06-29T22:00:00.000Z

1. Example reusable lambda function

In this example, we create a simple function that takes two arguments:

• date from which we want to subtract some seconds,
• hours - a number of hours we want to subtract.

Runnable example:

// ONLINE-RUNNER:browser;

const subtractHours = (date, hours) => {
  const result = new Date(date);
  result.setHours(result.getHours() - hours);
  return result;
};

const date = new Date('2021-06-30T00:00:00.000Z');

console.log(subtractHours(date, 2).toISOString());

Output:

2021-06-29T22:00:00.000Z

Note:

As you can see, the function also handles the case of the day change.

2. Extending existing Date class with Date.prototype

In this example, we add a function to the Date.prototype so we can use it on any date object.

// ONLINE-RUNNER:browser;

Date.prototype.subtractHours = function (hours) {
  let date = new Date(this.valueOf());
  date.setHours(date.getHours() - hours);
  return date;
};

let date = new Date('2021-06-30T00:00:00.000Z');

console.log(date.subtractHours(2).toISOString());

Output: 

2021-06-29T22:00:00.000Z