40 lines
1.4 KiB
JavaScript
40 lines
1.4 KiB
JavaScript
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import getISOWeekYear from '../getISOWeekYear/index.js';
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import startOfISOWeek from '../startOfISOWeek/index.js';
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/**
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* @name startOfISOWeekYear
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* @category ISO Week-Numbering Year Helpers
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* @summary Return the start of an ISO week-numbering year for the given date.
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*
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* @description
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* Return the start of an ISO week-numbering year,
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* which always starts 3 days before the year's first Thursday.
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* The result will be in the local timezone.
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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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* @param {Date|Number} date - the original date
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* @returns {Date} the start of an 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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* // The start of an ISO week-numbering year for 2 July 2005:
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* var result = startOfISOWeekYear(new Date(2005, 6, 2))
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* //=> Mon Jan 03 2005 00:00:00
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*/
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export default function startOfISOWeekYear(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 year = getISOWeekYear(dirtyDate);
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var fourthOfJanuary = new Date(0);
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fourthOfJanuary.setFullYear(year, 0, 4);
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fourthOfJanuary.setHours(0, 0, 0, 0);
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var date = startOfISOWeek(fourthOfJanuary);
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return date;
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}
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