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JavaScript - add hours to date

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Created by:

user4838

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

1. Example reusable lambda function

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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:

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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

Auto running

Output:

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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`

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

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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