34 lines
1.2 KiB
JavaScript
34 lines
1.2 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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import requiredArgs from "../_lib/requiredArgs/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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* @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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* 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 default function startOfISOWeekYear(dirtyDate) {
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requiredArgs(1, arguments);
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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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