getLocaleStartOfWeek

Signature

getLocaleStartOfWeek(value: string, locale: string | string[]): string

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 is invalid or locale is not a well-formed BCP 47 tag (ECMA-402 IsWellFormedLanguageTag). A well-formed tag with no matching locale data is not an error: it falls back to the host’s default locale, as ECMA-402 ResolveLocale requires.

Parameter	Type	Description
`value`	`string`	ISO 8601 date string
`locale`	`string` \| `string[]`	BCP 47 locale tag (e.g. “en-US”, “fr-FR”), or a preference list of tags (ECMA-402; the first with locale data is read). Required: omitted, or an empty list (which ECMA-402 would resolve to the host default), returns ""

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

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

getLocaleStartOfWeek("2024-02-29", "en-US") // "2024-02-25" (Sunday)