Function getISOWeek

pkgs/core/src/getISOWeek/index.ts:32–43

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

 * //=> 53
 */
export function getISOWeek(
  date: DateArg<Date> & {},
  options?: GetISOWeekOptions | undefined,
): number {
  const _date = toDate(date, options?.in);
  const diff = +startOfISOWeek(_date) - +startOfISOWeekYear(_date);

  // 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) + 1;
}