formatInTimezone

Formats a date in a specific IANA timezone using Intl.DateTimeFormat.

Returns null if the date or timezone is invalid.

Available since v2.0.0

Import

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

Signature

formatInTimezone(date: DateLike, tz: string, options: FormatInTimezoneOptions): string | null

Parameters

Parameter	Type	Description
date	DateLike	The date to format
tz	string	IANA timezone identifier (e.g. 'Asia/Tokyo')
options	FormatInTimezoneOptions	Optional locale and format configuration

Returns

string | null — A formatted date string, or null

Examples

formatInTimezone

formatInTimezone('2025-01-19T12:00:00Z', 'Asia/Tokyo')
// => "1/19/2025, 9:00:00 PM" (en-US default)

formatInTimezone('2025-01-19T12:00:00Z', 'Europe/Paris', {
  locale: 'fr-FR',
  formatOptions: { dateStyle: 'long', timeStyle: 'short' },
})
// => "19 janvier 2025, 13:00"

Related Types

FormatInTimezoneOptions

Options for formatInTimezone.

interface FormatInTimezoneOptions {
  formatOptions?: DateTimeFormatOptions;
  locale?: string;
}

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