Function differenceInMonths

pkgs/core/src/differenceInMonths/index.ts:28–64

(
  laterDate: DateArg<Date> & {},
  earlierDate: DateArg<Date> & {},
  options?: DifferenceInMonthsOptions | undefined,
)

 * //=> 7
 */
export function differenceInMonths(
  laterDate: DateArg<Date> & {},
  earlierDate: DateArg<Date> & {},
  options?: DifferenceInMonthsOptions | undefined,
): number {
  const [laterDate_, workingLaterDate, earlierDate_] = normalizeDates(
    options?.in,
    laterDate,
    laterDate,
    earlierDate,
  );

  const sign = compareAsc(workingLaterDate, earlierDate_);
  const difference = Math.abs(
    differenceInCalendarMonths(workingLaterDate, earlierDate_),
  );

  if (difference < 1) return 0;

  if (workingLaterDate.getMonth() === 1 && workingLaterDate.getDate() > 27)
    workingLaterDate.setDate(30);

  workingLaterDate.setMonth(workingLaterDate.getMonth() - sign * difference);

  let isLastMonthNotFull = compareAsc(workingLaterDate, earlierDate_) === -sign;

  if (
    isLastDayOfMonth(laterDate_) &&
    difference === 1 &&
    compareAsc(laterDate_, earlierDate_) === 1
  ) {
    isLastMonthNotFull = false;
  }

  const result = sign * (difference - +isLastMonthNotFull);
  return result === 0 ? 0 : result;
}