83 lines
3.3 KiB
JavaScript
83 lines
3.3 KiB
JavaScript
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import toDate from "../toDate/index.js";
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import differenceInCalendarDays from "../differenceInCalendarDays/index.js";
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import requiredArgs from "../_lib/requiredArgs/index.js"; // Like `compareAsc` but uses local time not UTC, which is needed
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// for accurate equality comparisons of UTC timestamps that end up
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// having the same representation in local time, e.g. one hour before
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// DST ends vs. the instant that DST ends.
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function compareLocalAsc(dateLeft, dateRight) {
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var diff = dateLeft.getFullYear() - dateRight.getFullYear() || dateLeft.getMonth() - dateRight.getMonth() || dateLeft.getDate() - dateRight.getDate() || dateLeft.getHours() - dateRight.getHours() || dateLeft.getMinutes() - dateRight.getMinutes() || dateLeft.getSeconds() - dateRight.getSeconds() || dateLeft.getMilliseconds() - dateRight.getMilliseconds();
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if (diff < 0) {
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return -1;
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} else if (diff > 0) {
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return 1; // Return 0 if diff is 0; return NaN if diff is NaN
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} else {
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return diff;
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}
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}
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/**
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* @name differenceInDays
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* @category Day Helpers
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* @summary Get the number of full days between the given dates.
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*
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* @description
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* Get the number of full day periods between two dates. Fractional days are
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* truncated towards zero.
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*
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* One "full day" is the distance between a local time in one day to the same
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* local time on the next or previous day. A full day can sometimes be less than
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* or more than 24 hours if a daylight savings change happens between two dates.
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*
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* To ignore DST and only measure exact 24-hour periods, use this instead:
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* `Math.floor(differenceInHours(dateLeft, dateRight)/24)|0`.
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*
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*
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* @param {Date|Number} dateLeft - the later date
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* @param {Date|Number} dateRight - the earlier date
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* @returns {Number} the number of full days according to the local timezone
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* @throws {TypeError} 2 arguments required
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*
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* @example
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* // How many full days are between
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* // 2 July 2011 23:00:00 and 2 July 2012 00:00:00?
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* const result = differenceInDays(
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* new Date(2012, 6, 2, 0, 0),
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* new Date(2011, 6, 2, 23, 0)
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* )
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* //=> 365
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* // How many full days are between
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* // 2 July 2011 23:59:00 and 3 July 2011 00:01:00?
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* const result = differenceInDays(
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* new Date(2011, 6, 3, 0, 1),
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* new Date(2011, 6, 2, 23, 59)
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* )
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* //=> 0
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* // How many full days are between
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* // 1 March 2020 0:00 and 1 June 2020 0:00 ?
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* // Note: because local time is used, the
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* // result will always be 92 days, even in
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* // time zones where DST starts and the
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* // period has only 92*24-1 hours.
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* const result = differenceInDays(
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* new Date(2020, 5, 1),
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* new Date(2020, 2, 1)
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* )
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//=> 92
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*/
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export default function differenceInDays(dirtyDateLeft, dirtyDateRight) {
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requiredArgs(2, arguments);
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var dateLeft = toDate(dirtyDateLeft);
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var dateRight = toDate(dirtyDateRight);
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var sign = compareLocalAsc(dateLeft, dateRight);
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var difference = Math.abs(differenceInCalendarDays(dateLeft, dateRight));
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dateLeft.setDate(dateLeft.getDate() - sign * difference); // Math.abs(diff in full days - diff in calendar days) === 1 if last calendar day is not full
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// If so, result must be decreased by 1 in absolute value
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var isLastDayNotFull = Number(compareLocalAsc(dateLeft, dateRight) === -sign);
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var result = sign * (difference - isLastDayNotFull); // Prevent negative zero
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return result === 0 ? 0 : result;
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}
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