55 lines
2.3 KiB
JavaScript
55 lines
2.3 KiB
JavaScript
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import toDate from '../toDate/index.js';
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import differenceInCalendarISOWeekYears from '../differenceInCalendarISOWeekYears/index.js';
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import compareAsc from '../compareAsc/index.js';
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import subISOWeekYears from '../subISOWeekYears/index.js';
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/**
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* @name differenceInISOWeekYears
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* @category ISO Week-Numbering Year Helpers
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* @summary Get the number of full ISO week-numbering years between the given dates.
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*
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* @description
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* Get the number of full ISO week-numbering years between the given dates.
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*
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* ISO week-numbering year: http://en.wikipedia.org/wiki/ISO_week_date
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*
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* ### v2.0.0 breaking changes:
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*
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* - [Changes that are common for the whole library](https://github.com/date-fns/date-fns/blob/master/docs/upgradeGuide.md#Common-Changes).
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*
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* - The function was renamed from `differenceInISOYears` to `differenceInISOWeekYears`.
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* "ISO week year" is short for [ISO week-numbering year](https://en.wikipedia.org/wiki/ISO_week_date).
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* This change makes the name consistent with
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* locale-dependent week-numbering year helpers, e.g., `addWeekYears`.
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*
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* @param {Date|Number} dateLeft - the later date
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* @param {Date|Number} dateRight - the earlier date
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* @returns {Number} the number of full ISO week-numbering years
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* @throws {TypeError} 2 arguments required
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*
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* @example
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* // How many full ISO week-numbering years are between 1 January 2010 and 1 January 2012?
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* var result = differenceInISOWeekYears(
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* new Date(2012, 0, 1),
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* new Date(2010, 0, 1)
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* )
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* //=> 1
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*/
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export default function differenceInISOWeekYears(dirtyDateLeft, dirtyDateRight) {
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if (arguments.length < 2) {
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throw new TypeError('2 arguments required, but only ' + arguments.length + ' present');
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}
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var dateLeft = toDate(dirtyDateLeft);
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var dateRight = toDate(dirtyDateRight);
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var sign = compareAsc(dateLeft, dateRight);
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var difference = Math.abs(differenceInCalendarISOWeekYears(dateLeft, dateRight));
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dateLeft = subISOWeekYears(dateLeft, sign * difference); // Math.abs(diff in full ISO years - diff in calendar ISO years) === 1
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// if last calendar ISO year is not full
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// If so, result must be decreased by 1 in absolute value
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var isLastISOWeekYearNotFull = compareAsc(dateLeft, dateRight) === -sign;
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var result = sign * (difference - isLastISOWeekYearNotFull); // Prevent negative zero
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return result === 0 ? 0 : result;
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}
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