47 lines
1.7 KiB
JavaScript
47 lines
1.7 KiB
JavaScript
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import { millisecondsInWeek } from "./constants.mjs";
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import { startOfISOWeek } from "./startOfISOWeek.mjs";
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import { getTimezoneOffsetInMilliseconds } from "./_lib/getTimezoneOffsetInMilliseconds.mjs";
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/**
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* @name differenceInCalendarISOWeeks
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* @category ISO Week Helpers
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* @summary Get the number of calendar ISO weeks between the given dates.
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*
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* @description
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* Get the number of calendar ISO weeks between the given dates.
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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 dateLeft - The later date
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* @param dateRight - The earlier date
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*
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* @returns The number of calendar ISO weeks
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*
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* @example
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* // How many calendar ISO weeks are between 6 July 2014 and 21 July 2014?
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* const result = differenceInCalendarISOWeeks(
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* new Date(2014, 6, 21),
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* new Date(2014, 6, 6)
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* )
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* //=> 3
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*/
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export function differenceInCalendarISOWeeks(dateLeft, dateRight) {
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const startOfISOWeekLeft = startOfISOWeek(dateLeft);
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const startOfISOWeekRight = startOfISOWeek(dateRight);
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const timestampLeft =
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+startOfISOWeekLeft - getTimezoneOffsetInMilliseconds(startOfISOWeekLeft);
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const timestampRight =
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+startOfISOWeekRight - getTimezoneOffsetInMilliseconds(startOfISOWeekRight);
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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((timestampLeft - timestampRight) / millisecondsInWeek);
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}
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// Fallback for modularized imports:
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export default differenceInCalendarISOWeeks;
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