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45 lines
1.4 KiB
45 lines
1.4 KiB
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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