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';
// or, from the all-in-one package (same code, one install):
import { addDays } from 'helpers4/date';

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

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

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

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

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)
Temporal.Instant | Temporal.ZonedDateTime — read via their epochMilliseconds property

type DateLike = Date | number | string | Temporal.Instant | Temporal.ZonedDateTime