59 lines
1.9 KiB
JavaScript
59 lines
1.9 KiB
JavaScript
import { millisecondsInWeek } from "./constants.mjs";
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import { startOfWeek } from "./startOfWeek.mjs";
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import { startOfWeekYear } from "./startOfWeekYear.mjs";
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import { toDate } from "./toDate.mjs";
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/**
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* The {@link getWeek} function options.
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*/
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/**
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* @name getWeek
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* @category Week Helpers
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* @summary Get the local week index of the given date.
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*
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* @description
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* Get the local week index of the given date.
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* The exact calculation depends on the values of
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* `options.weekStartsOn` (which is the index of the first day of the week)
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* and `options.firstWeekContainsDate` (which is the day of January, which is always in
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* the first week of the week-numbering year)
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*
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* Week numbering: https://en.wikipedia.org/wiki/Week#The_ISO_week_date_system
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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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* @param options - An object with options
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*
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* @returns The week
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*
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* @example
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* // Which week of the local week numbering year is 2 January 2005 with default options?
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* const result = getWeek(new Date(2005, 0, 2))
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* //=> 2
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*
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* @example
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* // Which week of the local week numbering year is 2 January 2005,
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* // if Monday is the first day of the week,
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* // and the first week of the year always contains 4 January?
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* const result = getWeek(new Date(2005, 0, 2), {
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* weekStartsOn: 1,
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* firstWeekContainsDate: 4
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* })
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* //=> 53
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*/
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export function getWeek(date, options) {
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const _date = toDate(date);
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const diff = +startOfWeek(_date, options) - +startOfWeekYear(_date, options);
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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) + 1;
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}
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// Fallback for modularized imports:
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export default getWeek;
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