date-utils.js

/**
 * Compares a date with today in the client's time zone. The comparison is day-wise,
 * so that all dates since today's midnight till the next midnight are considered "today".
 * Yesterday and tomorrow are separate from the past and future.
 *
 * @param dateRepresentation {string|number|Date}
 * @returns {number}
 *      +2 - date is in the future (after tomorrow)
 *      +1 - tomorrow
 *      0 - today
 *      -1 - yesterday
 *      -2 - date is in the past (before yesterday)
 */
export function relativeToLocaleToday(dateRepresentation) {
    return relativeToDate(dateRepresentation, Date.now());
}

/**
 * Compares a date with the reference date in the client's time zone. The comparison is day-wise,
 * so that all dates since the date's midnight till the next midnight are considered "same day".
 *
 * @param dateRepresentation {string|number|Date}
 * @param to {string|number|Date}
 * @returns {number}
 *      +2 - the date is after the reference date (2 days or more)
 *      +1 - the date is next to the reference date
 *      0 - the same day
 *      -1 - the date is one day before the reference date
 *      -2 - the date is earlier the reference date (2 days or more)
 */
export function relativeToDate(dateRepresentation, to) {
    const date = new Date(dateRepresentation);
    const referenceDate = new Date(to);
    if (referenceDate.toDateString() === date.toDateString()) {
        return 0;
    }

    const inFuture = date > referenceDate;
    const midnight = new Date(
        referenceDate.getFullYear(),
        referenceDate.getMonth(),
        referenceDate.getDate() + (inFuture ? 2 : -1)
    );
    if (inFuture) {
        return midnight > date
            ? 1
            : 2;
    }

    return midnight <= date
        ? -1
        : -2;
}

/**
 * Returns a range of dates between 'from' and 'to' exclusively: 'from', [N+1, N+2, ...], 'to'.
 * If 'from' is greater than 'to', the range is reversed: 'from', [N-1, N-2, ...], 'to'.
 * If 'include' argument is true and 'from' is the same day as 'to' (time may be different),
 * the range would contain only one element, which is max('from', 'to').
 *
 * @param from {string|number|Date}
 * @param to {string|number|Date}
 * @param [include=false] {boolean} -
 *      include 'from' and/or 'to' to the resulting array.
 * @param [transform=null] {null|true|Function} -
 *      if null, time of the dates between 'from' and 'to' would be the same as 'from'.
 *      if true, time of the dates would be set to locale midnight,
 *      if Function, each Date in the range would be passed to the function,
 *          returned value is used in the resulting array.
 * @returns {[]}
 */
export function datesRange(from, to, {include = false, transform = null} = {}) {
    const range = [];
    from = new Date(from);
    to = new Date(to);
    const reversed = from > to;
    if (reversed) {
        [from, to] = [to, from];
    }
    const insert = reversed ? range.unshift.bind(range) : range.push.bind(range);
    const formatter = typeof transform === 'function' ? transform : function (d) {
        if (transform === true) {
            d.setHours(0);
            d.setMinutes(0);
            d.setSeconds(0);
            d.setMilliseconds(0);
        }

        return d;
    };
    const fromToOffset = relativeToDate(from, to);
    if (fromToOffset < -1) {
        const toMidnight = new Date(to.getFullYear(), to.getMonth(), to.getDate());
        const nextDay = new Date(from);
        while (nextDay.setDate(nextDay.getDate() + 1) < toMidnight) {
            insert(formatter(new Date(nextDay)));
        }
    }

    if (include) {
        insert(formatter(to));
        if (fromToOffset) {
            const resultFrom = formatter(from);
            if (reversed) {
                range.push(resultFrom);
            } else {
                range.unshift(resultFrom);
            }
        }
    }

    return range;
}