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 王天杨
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import { compareAsc } from "./compareAsc.mjs";
import { differenceInCalendarISOWeekYears } from "./differenceInCalendarISOWeekYears.mjs";
import { subISOWeekYears } from "./subISOWeekYears.mjs";
import { toDate } from "./toDate.mjs";
/**
* @name differenceInISOWeekYears
* @category ISO Week-Numbering Year Helpers
* @summary Get the number of full ISO week-numbering years between the given dates.
*
* @description
* Get the number of full ISO week-numbering years between the given dates.
*
* ISO week-numbering year: http://en.wikipedia.org/wiki/ISO_week_date
*
* @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 ISO week-numbering years
*
* @example
* // How many full ISO week-numbering years are between 1 January 2010 and 1 January 2012?
* const result = differenceInISOWeekYears(
* new Date(2012, 0, 1),
* new Date(2010, 0, 1)
* )
* //=> 1
*/
export function differenceInISOWeekYears(dateLeft, dateRight) {
let _dateLeft = toDate(dateLeft);
const _dateRight = toDate(dateRight);
const sign = compareAsc(_dateLeft, _dateRight);
const difference = Math.abs(
differenceInCalendarISOWeekYears(_dateLeft, _dateRight),
);
_dateLeft = subISOWeekYears(_dateLeft, sign * difference);
// Math.abs(diff in full ISO years - diff in calendar ISO years) === 1
// if last calendar ISO year is not full
// If so, result must be decreased by 1 in absolute value
const isLastISOWeekYearNotFull = Number(
compareAsc(_dateLeft, _dateRight) === -sign,
);
const result = sign * (difference - isLastISOWeekYearNotFull);
// Prevent negative zero
return result === 0 ? 0 : result;
}
// Fallback for modularized imports:
export default differenceInISOWeekYears;
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