Function durationInMonths

packages/graph/src/TemporalTypes.ts:1767–1790

(start: TemporalValue, end: TemporalValue)

 * Compute the duration between two temporal values in months only.
 */
export function durationInMonths(start: TemporalValue, end: TemporalValue): DurationValue | null {
  if (
    (start instanceof DateValue ||
      start instanceof LocalDateTimeValue ||
      start instanceof DateTimeValue) &&
    (end instanceof DateValue || end instanceof LocalDateTimeValue || end instanceof DateTimeValue)
  ) {
    const startYear = start.year;
    const startMonth = start.month;
    const endYear = end.year;
    const endMonth = end.month;

    let months = (endYear - startYear) * 12 + (endMonth - startMonth);
    const startDay = start.day;
    const endDay = end.day;

    if (endDay < startDay) {
      months--;
    }

    return new DurationValue(months, 0, 0, 0);
  }
  return null;
}

/**
 * Compute the duration between two temporal values in days only.