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  3. Add Hours to a Date in JavaScript or Node.js

Add Hours to a Date in JavaScript or Node.js

Working with dates is a common task in application development. You may provide ways to adjust dates and timestamps in your app. One of these tasks may be adding hours to a date in JavaScript. For example, you may allow users to tell your app to „remind me in 1 hour“ or „remind in 8 hours“ of something.

This tutorial shows you how to add hours do a date in JavaScript!

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Adding Hours to a Date in JavaScript

JavaScript natively comes with a Date type and provides lots of useful methods to interact with dates. The two methods of interest when interacting with hours are Date#setHours and Date#getHours.

The getHours returns the current number of hours of a given date. And the setHours method changes the hour of a given date instance.

The nice thing here is that JavaScript takes care of changing the day/month/year in case the added hours shift something of that.

Here's a sample function adding a given number of hours to a date:

/**
 * Returns a date instance with added `hours` of delay.
 *
 * @param {Number} hours - the number of hours to add
 * @param {Date|undefined} date
 *
 * @returns {Date}
 */
function addHours (hours, date = new Date()) {  
  if (typeof hours !== 'number') {
    throw new Error('Invalid "hours" argument')
  }

  if (!(date instanceof Date)) {
    throw new Error('Invalid "date" argument')
  }

  date.setHours(date.getHours() + hours)

  return date
}

Please notice, the sample addHours function from above supports a second, optional date argument which defaults to “now”. You may remove the “now” default or use a different in your application.

Here’s how you can use the addHours utility function. The last example adds five hours to New Year’s eve which requires an hour, day, and year switch and JavaScript handles all that for us:

addHours(1)  
// Tue Nov 15 2022 08:19:17 GMT+0100

addHours(4)  
// Tue Nov 15 2022 11:19:17 GMT+0100

addHours(5, new Date('2022-12-31 22:00'))  
// Sun Jan 01 2023 03:00:00 GMT+0100

Enjoy!

Mentioned Resources

Marcus Pöhls

Marcus is a fullstack JS developer. He’s passionate about the hapi framework for Node.js and loves to build web apps and APIs. Creator of Futureflix and the “learn hapi” learning path.

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