Function getISOWeeksInYear

pkgs/core/src/getISOWeeksInYear/index.ts:31–43

(
  date: DateArg<Date> & {},
  options?: GetISOWeeksInYearOptions | undefined,
)

 * //=> 53
 */
export function getISOWeeksInYear(
  date: DateArg<Date> & {},
  options?: GetISOWeeksInYearOptions | undefined,
): number {
  const thisYear = startOfISOWeekYear(date, options);
  const nextYear = startOfISOWeekYear(addWeeks(thisYear, 60));
  const diff = +nextYear - +thisYear;

  // Round the number of weeks to the nearest integer because the number of
  // milliseconds in a week is not constant (e.g. it's different in the week of
  // the daylight saving time clock shift).
  return Math.round(diff / millisecondsInWeek);
}