getLocaleStartOfWeek

Signature

getLocaleStartOfWeek(value: string, locale: string): string

import { getLocaleStartOfWeek } from "@northguild/gmt/plain/calculate";

Return the start of the week containing value, using locale’s

• first day of week (e.g. en-US: Sunday, fr-FR: Monday).
• Resolves the locale’s first day of week via Intl.Locale.prototype.weekInfo.
• Falls back to Monday if the runtime’s weekInfo data doesn’t resolve a first day for the locale.
• Distinct from startOfDate(value, "week", { weekStartsOn }), which takes an explicit ISO-biased weekStartsOn option instead of deriving it from a locale.
• Returns “” if value or locale is invalid.

Parameters

Parameter	Type	Description
value	string	ISO 8601 date string
locale	string	BCP 47 locale tag (e.g. “en-US”, “fr-FR”)

Returns

ISO 8601 date string for the start of value’s locale-relative week, or “” on invalid input

Examples

getLocaleStartOfWeek("2024-02-29", "en-US") // "2024-02-25" (Sunday)
getLocaleStartOfWeek("2024-02-29", "fr-FR") // "2024-02-26" (Monday)
getLocaleStartOfWeek("invalid-date", "en-US") // ""
getLocaleStartOfWeek("2024-02-29", "not-a-locale") // ""

Source

plain/calculate/getLocaleStartOfWeek.ts