56 lines
2.0 KiB
JavaScript
56 lines
2.0 KiB
JavaScript
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import toDate from '../toDate/index.js';
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import startOfISOWeek from '../startOfISOWeek/index.js';
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/**
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* @name getISOWeekYear
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* @category ISO Week-Numbering Year Helpers
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* @summary Get the ISO week-numbering year of the given date.
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*
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* @description
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* Get the ISO week-numbering year of the given date,
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* which always starts 3 days before the year's first Thursday.
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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 `getISOYear` to `getISOWeekYear`.
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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., `getWeekYear`.
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*
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* @param {Date|Number} date - the given date
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* @returns {Number} the ISO week-numbering year
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* @throws {TypeError} 1 argument required
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*
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* @example
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* // Which ISO-week numbering year is 2 January 2005?
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* var result = getISOWeekYear(new Date(2005, 0, 2))
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* //=> 2004
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*/
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export default function getISOWeekYear(dirtyDate) {
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if (arguments.length < 1) {
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throw new TypeError('1 argument required, but only ' + arguments.length + ' present');
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}
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var date = toDate(dirtyDate);
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var year = date.getFullYear();
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var fourthOfJanuaryOfNextYear = new Date(0);
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fourthOfJanuaryOfNextYear.setFullYear(year + 1, 0, 4);
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fourthOfJanuaryOfNextYear.setHours(0, 0, 0, 0);
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var startOfNextYear = startOfISOWeek(fourthOfJanuaryOfNextYear);
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var fourthOfJanuaryOfThisYear = new Date(0);
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fourthOfJanuaryOfThisYear.setFullYear(year, 0, 4);
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fourthOfJanuaryOfThisYear.setHours(0, 0, 0, 0);
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var startOfThisYear = startOfISOWeek(fourthOfJanuaryOfThisYear);
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if (date.getTime() >= startOfNextYear.getTime()) {
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return year + 1;
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} else if (date.getTime() >= startOfThisYear.getTime()) {
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return year;
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} else {
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return year - 1;
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}
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}
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