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