@burglekitt/gmt
Version:
Temporal-based date and time utilities with timezone support and polyfill integration
32 lines (31 loc) • 1.43 kB
JavaScript
/**
* Resolve the minimum number of days a week must have in January for that
* week to count as a locale's week 1, via `Intl.Locale.prototype.weekInfo`.
*
* - Returns `null` if `locale` is not a valid BCP 47 tag.
* - Falls back to `4` (matching ISO 8601's rule — week 1 is the first
* week with at least 4 days in January, equivalently the week
* containing Jan 4) if `weekInfo` is unavailable on the runtime (older
* engines) or unresolvable for the given locale. This mirrors
* `getLocaleFirstDayOfWeek`'s fallback-to-ISO-default pattern.
* - Observed on Node 24 (V8/ICU 78): `weekInfo` omits `minimalDays`
* entirely, for every locale, even though Node 20/22 (ICU 77) populate
* it — so this fallback engages universally on that runtime rather
* than only for locales missing data. `getLocaleWeekYear` and
* `getWeeksInLocaleWeekYear` therefore lose locale-specific
* minimal-days behavior (silently degrading to the ISO value) on
* runtimes where the engine doesn't expose it, which is worth knowing
* before treating a Node-version-only test failure as a real bug.
*/
export function getLocaleMinimalDaysInFirstWeek(locale) {
try {
const weekInfo = new Intl.Locale(locale).weekInfo;
if (!weekInfo || typeof weekInfo.minimalDays !== "number") {
return 4;
}
return weekInfo.minimalDays;
}
catch {
return null;
}
}