Function tzOffset

pkgs/tz/src/tzOffset/index.ts:22–48

(timeZone: string | undefined, date: Date)

 * @returns UTC offset in minutes (e.g., `480` for date in UTC+8).
 */
export function tzOffset(timeZone: string | undefined, date: Date): number {
  try {
    // Create `Intl.DateTimeFormat` with `"longOffset"` that gives us consistent
    // date strings like `"5/19/2026, GMT-08:00"`.
    const format = (offsetFormatCache[timeZone!] ||= new Intl.DateTimeFormat(
      "en-US",
      { timeZone, timeZoneName: "longOffset" },
    ).format);

    // Get `"-08:00"`.
    const offsetStr = format(date).split("GMT")[1]!;

    // Avoid parsing the same offset string.
    if (offsetStr in offsetCache) return offsetCache[offsetStr]!;

    // Calculate offset from `["-08", "00"]` and cache it.
    return calcOffset(offsetStr, offsetStr.split(":"));
  } catch {
    // Fallback to manual parsing if the runtime doesn't support
    // `±HH:MM/±HHMM/±HH`. See: https://github.com/nodejs/node/issues/53419.
    if (timeZone! in offsetCache) return offsetCache[timeZone!]!;
    const captures = timeZone?.match(offsetRe);
    if (captures) return calcOffset(timeZone!, captures.slice(1));

    return NaN;
  }
}

const offsetRe = /([+-]\d\d):?(\d\d)?/;