@burglekitt/gmt/dist/plain/locale/getLocaleEraNames.js

Temporal-based date and time utilities with timezone support and polyfill integration

import { Temporal } from "@js-temporal/polyfill";
/**
 * Return a locale's Gregorian era names as [BCE-label, CE-label].
 *
 * - The two-element array is [Before Common Era label, Common Era label].
 * - Uses the host runtime's `Intl` data via `Intl.DateTimeFormat`, so output
 *   depends on the runtime's ICU build (full-ICU runtimes localize every
 *   locale; partial-ICU runtimes fall back to English).
 * - If a locale has no distinct BCE/CE era names, both array elements
 *   contain the same string — the function never returns a sentinel for
 *   a valid locale, only for invalid input.
 * - Returns `[]` if `locale` is not a valid BCP 47 tag.
 *
 * @param locale BCP 47 locale tag (e.g. "en-US", "fr-FR", "ar-SA")
 * @param style Optional name style: `"long"` (default), `"short"`, or `"narrow"`
 * @returns 2-element `[BCE-label, CE-label]` array, or `[]` on invalid input
 *
 * @example getLocaleEraNames("en-US") // ["Before Christ", "Anno Domini"]
 * @example getLocaleEraNames("de-DE", "short") // ["v. Chr.", "n. Chr."]
 * @example getLocaleEraNames("ja-JP", "narrow") // ["BC", "AD"]
 * @example getLocaleEraNames("not-a-locale") // []
 */
export function getLocaleEraNames(locale, style = "long") {
    if (typeof locale !== "string")
        return [];
    try {
        new Intl.Locale(locale);
    }
    catch {
        return [];
    }
    try {
        const resolved = style === "short" || style === "narrow" ? style : "long";
        const formatter = new Intl.DateTimeFormat(locale, {
            calendar: "gregory",
            era: resolved,
            timeZone: "UTC",
        });
        // Year 1 BC (proleptic Gregorian) — Temporal represents 1 BC as year 0.
        const bceInstant = Temporal.ZonedDateTime.from({
            year: 0,
            month: 1,
            day: 1,
            hour: 12,
            timeZone: "UTC",
            calendar: "gregory",
        }).toInstant();
        // Year 1 AD (proleptic Gregorian).
        const ceInstant = Temporal.ZonedDateTime.from({
            year: 1,
            month: 1,
            day: 1,
            hour: 12,
            timeZone: "UTC",
            calendar: "gregory",
        }).toInstant();
        const bceParts = formatter.formatToParts(bceInstant.epochMilliseconds);
        const bceEra = bceParts.find((part) => part.type === "era")?.value ?? "";
        const ceParts = formatter.formatToParts(ceInstant.epochMilliseconds);
        const ceEra = ceParts.find((part) => part.type === "era")?.value ?? "";
        return [bceEra, ceEra];
    }
    catch {
        return [];
    }
}