38 lines
1.3 KiB
JavaScript
38 lines
1.3 KiB
JavaScript
import { getISOWeekYear } from "./getISOWeekYear.mjs";
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import { startOfISOWeek } from "./startOfISOWeek.mjs";
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import { constructFrom } from "./constructFrom.mjs";
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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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* @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).
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*
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* @param date - The original date
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*
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* @returns The start of an ISO week-numbering year
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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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* const 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 function startOfISOWeekYear(date) {
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const year = getISOWeekYear(date);
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const fourthOfJanuary = constructFrom(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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return startOfISOWeek(fourthOfJanuary);
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}
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// Fallback for modularized imports:
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export default startOfISOWeekYear;
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