JavaScript - add hours to date

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

1. Example reusable lambda function

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

• date to which we want to add some hours,
• hours - a number of hours we want to add.

Runnable example:

// ONLINE-RUNNER:browser;

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


// Usage example:

const date = new Date('2021-08-30T23:00:00.000Z');

console.log(addHours(date, 2).toISOString());  // 2021-08-31T01:00:00.000Z

Output:

2021-08-31T01:00:00.000Z

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.addHours = function (hours) {
  let date = new Date(this.valueOf());
  date.setHours(date.getHours() + hours);
  return date;
};


// Usage example:

let date = new Date('2021-08-30T23:00:00.000Z');

console.log(date.addHours(2).toISOString());  // 2021-08-31T01:00:00.000Z

Output: 

2021-08-31T01:00:00.000Z