39 lines
1.4 KiB
JavaScript
39 lines
1.4 KiB
JavaScript
import { addWeeks } from "./addWeeks.mjs";
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import { millisecondsInWeek } from "./constants.mjs";
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import { startOfISOWeekYear } from "./startOfISOWeekYear.mjs";
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/**
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* @name getISOWeeksInYear
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* @category ISO Week-Numbering Year Helpers
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* @summary Get the number of weeks in an ISO week-numbering year of the given date.
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*
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* @description
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* Get the number of weeks in an ISO week-numbering year of the given date.
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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 given date
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*
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* @returns The number of ISO weeks in a year
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*
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* @example
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* // How many weeks are in ISO week-numbering year 2015?
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* const result = getISOWeeksInYear(new Date(2015, 1, 11))
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* //=> 53
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*/
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export function getISOWeeksInYear(date) {
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const thisYear = startOfISOWeekYear(date);
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const nextYear = startOfISOWeekYear(addWeeks(thisYear, 60));
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const diff = +nextYear - +thisYear;
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// Round the number of weeks to the nearest integer because the number of
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// milliseconds in a week is not constant (e.g. it's different in the week of
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// the daylight saving time clock shift).
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return Math.round(diff / millisecondsInWeek);
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}
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// Fallback for modularized imports:
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export default getISOWeeksInYear;
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