Function localTimeToTimestamp

src/time/localized-time.ts:78–98

(parts: WallClock, timezone?: string)

 * of drifting backwards into the gap (which used to yield a past date).
 */
export function localTimeToTimestamp(parts: WallClock, timezone?: string): number {
  const guess = Date.UTC(
    parts.year, parts.month - 1, parts.day,
    parts.hour, parts.minute, parts.second, parts.millisecond
  );

  const firstOffset = getOffsetMinutes(new Date(guess), timezone);
  const candidate1 = guess - firstOffset * 60000;

  const secondOffset = getOffsetMinutes(new Date(candidate1), timezone);
  if (secondOffset === firstOffset) {
    return candidate1;
  }

  const candidate2 = guess - secondOffset * 60000;
  if (readsBackTo(candidate1, parts, timezone)) return candidate1;
  if (readsBackTo(candidate2, parts, timezone)) return candidate2;

  // Non-existent local time (spring-forward gap): resolve forward.
  return Math.max(candidate1, candidate2);
}

// Constructing an Intl.DateTimeFormat is expensive (~90us each on V8) while
// reusing one is ~16x cheaper. A formatter only depends on the timezone, so we