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JavaScript - add milliseconds to date

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Created by:

Gigadude

791

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

Runnable example:

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const addMilliseconds = (date, milliseconds) => {
  const result = new Date(date);
  result.setMilliseconds(result.getMilliseconds() + milliseconds);
  return result;
};
​
let date = new Date('2021-08-30T00:00:00.000Z');
​
console.log(addMilliseconds(date, 5).toISOString());  // 2021-08-30T00:00:00.005Z

Auto running

Output:

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2021-08-30T00:00:00.005Z

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.addMilliseconds = function (milliseconds) {
  let date = new Date(this.valueOf());
  date.setMilliseconds(date.getMilliseconds() + milliseconds);
  return date;
};
​
let date = new Date('2021-08-30T00:00:00.000Z');
​
console.log(date.addMilliseconds(5).toISOString());  // 2021-08-30T00:00:00.005Z