JavaScript - add days to date

In this article, we would like to show you how to add days 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 days,
• days - a number of days we want to add.

Runnable example:

// ONLINE-RUNNER:browser;

const addDays = (date, days) => {
  let result = new Date(date);
  result.setDate(result.getDate() + days);
  return result;
};

let date = new Date('2021-08-30T23:59:59.000Z');
let result = addDays(date, 1);

console.log(result.toISOString());  // 2021-08-31T23:59:59.000Z

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.addDays = function (days) {
  let date = new Date(this.valueOf());
  date.setDate(date.getDate() + days);
  return date;
};

let date = new Date('2021-08-30T23:59:59.000Z');
let result = date.addDays(1)

console.log(result.toISOString());  // 2021-08-31T23:59:59.000Z