timepiece/node_modules/date-fns/differenceInYears.mjs

48 lines
1.7 KiB
JavaScript
Raw Normal View History

2024-05-14 14:54:12 +00:00
import { compareAsc } from "./compareAsc.mjs";
import { differenceInCalendarYears } from "./differenceInCalendarYears.mjs";
import { toDate } from "./toDate.mjs";
/**
* @name differenceInYears
* @category Year Helpers
* @summary Get the number of full years between the given dates.
*
* @description
* Get the number of full years between the given dates.
*
* @typeParam DateType - The `Date` type, the function operates on. Gets inferred from passed arguments. Allows to use extensions like [`UTCDate`](https://github.com/date-fns/utc).
*
* @param dateLeft - The later date
* @param dateRight - The earlier date
*
* @returns The number of full years
*
* @example
* // How many full years are between 31 December 2013 and 11 February 2015?
* const result = differenceInYears(new Date(2015, 1, 11), new Date(2013, 11, 31))
* //=> 1
*/
export function differenceInYears(dateLeft, dateRight) {
const _dateLeft = toDate(dateLeft);
const _dateRight = toDate(dateRight);
const sign = compareAsc(_dateLeft, _dateRight);
const difference = Math.abs(differenceInCalendarYears(_dateLeft, _dateRight));
// Set both dates to a valid leap year for accurate comparison when dealing
// with leap days
_dateLeft.setFullYear(1584);
_dateRight.setFullYear(1584);
// Math.abs(diff in full years - diff in calendar years) === 1 if last calendar year is not full
// If so, result must be decreased by 1 in absolute value
const isLastYearNotFull = compareAsc(_dateLeft, _dateRight) === -sign;
const result = sign * (difference - +isLastYearNotFull);
// Prevent negative zero
return result === 0 ? 0 : result;
}
// Fallback for modularized imports:
export default differenceInYears;