@burglekitt/gmt/dist/zoned/validate/hasDaylightSaving.js

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

import { Temporal } from "@js-temporal/polyfill";
/**
 * Check whether an IANA timeZone identifier observes daylight saving time.
 *
 * - Compares UTC offsets at two dates six months apart (January and July).
 * - A zone is considered to have DST if its offset differs between the two dates.
 * - Returns false for invalid or unresolvable timeZone identifiers.
 *
 * @param timeZone timeZone identifier to check
 * @returns boolean indicating whether the timeZone observes DST
 *
 * @example hasDaylightSaving("America/New_York") // true
 * @example hasDaylightSaving("Europe/Berlin")     // true
 * @example hasDaylightSaving("Asia/Tokyo")        // false
 * @example hasDaylightSaving("UTC")               // false
 * @example hasDaylightSaving("Invalid/Zone")      // false
 */
export function hasDaylightSaving(timeZone) {
    try {
        const zdtJanuary = Temporal.ZonedDateTime.from({
            year: 2024,
            month: 1,
            day: 15,
            hour: 12,
            minute: 0,
            second: 0,
            timeZone,
        });
        const zdtJuly = Temporal.ZonedDateTime.from({
            year: 2024,
            month: 7,
            day: 15,
            hour: 12,
            minute: 0,
            second: 0,
            timeZone,
        });
        return zdtJanuary.offsetNanoseconds !== zdtJuly.offsetNanoseconds;
    }
    catch {
        return false;
    }
}