locale

Thin wrappers over Intl for locale-aware labels and formatting. Pass a BCP-47 locale string (for example 'en-US', 'en-GB', or 'ar'); everything is computed on demand, and no locale data is bundled beyond what the runtime already provides.

DatePicker uses these to render its calendar header, weekday row, and field text.

getFirstDayOfWeek(locale)

function getFirstDayOfWeek(locale: string): number

Returns the locale's first day of the week, read from Intl.Locale's weekInfo (with a getWeekInfo() fallback for older runtimes).

Parameter	Type	Description
locale	string	BCP-47 locale tag.

Returns: number where 0 is Sunday … 6 is Saturday. When the locale is invalid or the runtime does not expose week info, it falls back to 1 (Monday).

import { getFirstDayOfWeek } from '@myghf/ui'

getFirstDayOfWeek('en-US') // → 0 (Sunday)
getFirstDayOfWeek('en-GB') // → 1 (Monday)
getFirstDayOfWeek('de-DE') // → 1 (Monday)

getWeekdayLabels(locale, weekStartsOn)

function getWeekdayLabels(locale: string, weekStartsOn: number): string[]

Builds seven short weekday labels (for example 'Sun', 'Mon') in the given locale, rotating so the first label is weekStartsOn. The start index is normalised modulo 7, so negative and out-of-range values wrap.

Parameter	Type	Description
locale	string	BCP-47 locale tag.
weekStartsOn	number	First day of the week; 0 = Sunday … 6 = Saturday.

Returns: string[] of exactly seven labels, starting at weekStartsOn.

import { getFirstDayOfWeek, getWeekdayLabels } from '@myghf/ui'

const first = getFirstDayOfWeek('en-US') // 0
const labels = getWeekdayLabels('en-US', first)
// ['Sun', 'Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat']

getWeekdayLabels('en-GB', 1)[0] // → 'Mon'

getMonthLabel(date, locale)

function getMonthLabel(date: Date, locale: string): string

Formats a long month name plus year, for a calendar header.

Parameter	Type	Description
date	Date	Any date in the target month.
locale	string	BCP-47 locale tag.

Returns: string such as 'January 2026', localised to locale.

import { getMonthLabel } from '@myghf/ui'

getMonthLabel(new Date(2026, 0, 15), 'en-US') // → 'January 2026'
getMonthLabel(new Date(2026, 0, 15), 'fr-FR') // → 'janvier 2026'

formatLocalizedDate(date, locale)

function formatLocalizedDate(date: Date, locale: string): string

Formats a date with Intl.DateTimeFormat's { dateStyle: 'medium' }.

Parameter	Type	Description
date	Date	The date to format.
locale	string	BCP-47 locale tag.

Returns: string such as 'Jan 15, 2026' (en-US) or '15 janv. 2026' (fr-FR).

import { formatLocalizedDate } from '@myghf/ui'

formatLocalizedDate(new Date(2026, 0, 15), 'en-US') // → 'Jan 15, 2026'

formatLocalizedTime(date, locale, hourFormat)

function formatLocalizedTime(date: Date, locale: string, hourFormat: '12' | '24'): string

Formats the time of day, forcing a 12- or 24-hour clock regardless of the locale's default.

Parameter	Type	Description
date	Date	The date whose time is formatted.
locale	string	BCP-47 locale tag.
hourFormat	'12' | '24'	'24' uses hourCycle: 'h23'; '12' uses hour12: true.

Returns: string such as '09:30' ('24') or '9:30 AM' ('12').

import { formatLocalizedTime } from '@myghf/ui'

const at = new Date(2026, 0, 1, 9, 30)
formatLocalizedTime(at, 'en-GB', '24') // → '09:30'
formatLocalizedTime(at, 'en-US', '12') // → '9:30 AM'

Notes

• These are display helpers only. To parse or move between Date and the picker's value types, use the date utilities.
• Formatting depends on the runtime's ICU data. Node and modern browsers ship full ICU, so output matches between server and client; very small ICU builds may fall back to a default locale.
• Pass DatePicker's locale prop to keep the field and this formatting in agreement.