index.js
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import getISOWeekYear from '../getISOWeekYear/index.js';
import startOfISOWeek from '../startOfISOWeek/index.js';
import requiredArgs from '../_lib/requiredArgs/index.js';
/**
* @name startOfISOWeekYear
* @category ISO Week-Numbering Year Helpers
* @summary Return the start of an ISO week-numbering year for the given date.
*
* @description
* Return the start of an ISO week-numbering year,
* which always starts 3 days before the year's first Thursday.
* The result will be in the local timezone.
*
* ISO week-numbering year: http://en.wikipedia.org/wiki/ISO_week_date
*
* ### v2.0.0 breaking changes:
*
* - [Changes that are common for the whole library](https://github.com/date-fns/date-fns/blob/master/docs/upgradeGuide.md#Common-Changes).
*
* @param {Date|Number} date - the original date
* @returns {Date} the start of an ISO week-numbering year
* @throws {TypeError} 1 argument required
*
* @example
* // The start of an ISO week-numbering year for 2 July 2005:
* var result = startOfISOWeekYear(new Date(2005, 6, 2))
* //=> Mon Jan 03 2005 00:00:00
*/
export default function startOfISOWeekYear(dirtyDate) {
requiredArgs(1, arguments);
var year = getISOWeekYear(dirtyDate);
var fourthOfJanuary = new Date(0);
fourthOfJanuary.setFullYear(year, 0, 4);
fourthOfJanuary.setHours(0, 0, 0, 0);
var date = startOfISOWeek(fourthOfJanuary);
return date;
}