addDays

Adds days to a date.

Returns a new Date — the original is never mutated. Returns null if the input is invalid.

Available since v2.0.0

Import

import { addDays } from '@helpers4/date';

Signature

addDays(date: DateLike, amount: number): Date | null

Parameters

Parameter	Type	Description
date	DateLike	The base date
amount	number	Number of days to add (negative to subtract)

Returns

Date | null — A new Date, or null if the input is invalid

Examples

addDays

addDays('2025-01-19', 10)   // => Date(2025-01-29)
addDays('2025-01-19', -5)   // => Date(2025-01-14)

Related Types

DateLike

A value that can be converted to a Date.

• Date — used as-is (validated for Invalid Date)
• number — treated as a timestamp (seconds or milliseconds, auto-detected); 0 is treated as invalid and produces null in ensureDate
• string — parsed via new Date(string)
• EpochMilliseconds — any object with a epochMilliseconds property (e.g. Temporal.Instant, Temporal.ZonedDateTime)

// TODO: When the Temporal API reaches Stage 4 and is available without // flags in all major runtimes, consider narrowing the union to the // concrete Temporal types for stricter type-checking.

type DateLike = Date | number | string | EpochMilliseconds

EpochMilliseconds

An object that exposes an epoch timestamp in milliseconds.

This structural type is satisfied by Temporal.Instant and Temporal.ZonedDateTime (and any future object that carries the same property), so callers can pass Temporal values without importing them.

interface EpochMilliseconds {
  epochMilliseconds: number;
}

Source

View source on GitHub