48 lines
1.7 KiB
JavaScript
48 lines
1.7 KiB
JavaScript
|
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;
|