46 lines
1.4 KiB
JavaScript
46 lines
1.4 KiB
JavaScript
var parse = require('../parse/index.js')
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var startOfISOWeek = require('../start_of_iso_week/index.js')
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/**
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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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* @param {Date|String|Number} date - the given date
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* @returns {Number} the ISO week-numbering year
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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 = getISOYear(new Date(2005, 0, 2))
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* //=> 2004
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*/
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function getISOYear (dirtyDate) {
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var date = parse(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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module.exports = getISOYear
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