Date difference in Javascript (ignoring time of day)

Question

I\'m writing an equipment rental application where clients are charged a fee for renting equipment based on the duration (in days) of the rental. So, basically, (daily fee *

Answer 1

I would also suggest having a look at the incredible moment.js library. It has a versatile diff function, which you can use to solve the above example as follows:

function is_same_date(startDate, endDate) {
   var startMoment = moment(startDate).clone().startOf('day'),
       endMoment = moment(endDate).clone().startOf('day');
   return startMoment.diff(endMoment, 'days') == 0;
}

Here are some examples using moment.js diff:

> d1 = new Date(2012,04,04,0,0)
Fri May 04 2012 00:00:00 GMT-0400 (EDT)

> d2 = new Date(2012,04,03,23,0)
Thu May 03 2012 23:00:00 GMT-0400 (EDT)

> d3 = new Date(2012,04,05,23,0)
Sat May 05 2012 23:00:00 GMT-0400 (EDT)

> moment(d2).diff(d1, 'days')
0

> moment(d1).diff(d2, 'days')
0

> moment(d1).diff(d3, 'days') // uh oh. this is why we use `startOf`
-2

> moment(d2).diff(d3, 'days')
-2

> moment(d3).startOf('day') // this modified d3, sets the time to 00:00:00.0000
> d3
Sat May 05 2012 00:00:00 GMT-0400 (EDT)

If timezones are a concern, you can also use moment.utc() to convert to a normalized timezone.

Answer 2

I used to check the result of datediff function which uses .getTime() with Excel for the 18th century. The result returns correct. I have another method to calculate different days:

    function DaysOfYear(nYear) {
        if ((nYear % 4) == 0) {
            return 366;
        }
        else {
            return 365;
        }
    }


    function DiffDays(fDate, tDate) {
        var fYear = fDate.getFullYear();
        var tYear = tDate.getFullYear();
        var fMonth = fDate.getMonth();
        var tMonth = tDate.getMonth();
        var fDay = fDate.getDate();
        var tDay = tDate.getDate();
        var nDays = 0;

        if (tYear > fYear) {   // different year
            // remain days of from year
            nDays = DaysOfYear(fYear) - YTD_Days(fDate);
            // days of between fYear to tYear
            for (y = (fYear + 1); y < tYear; y++) {
                nDays = nDays + DaysOfYear(y);
            }
            // days from the beginning of tYear
            nDays = nDays + YTD_Days(tDate);
        }
        else {   // in the same year
            nDays = YTD_Days(tDate) - YTD_Days(fDate);
        };
        return nDays;
    }

    function YTD_Days(dDate) {
        var y = dDate.getFullYear();
        var m = dDate.getMonth();
        var nDays = 0

        for (i = 0; i < m; i++) {
            switch (i) {
                case 0:     // January
                    nDays = nDays + 31;
                    break;
                case 1:     // February
                    if ((y % 4) == 0) {
                        nDays = nDays + 29;
                    }
                    else {
                        nDays = nDays + 28;
                    };
                    break;
                case 2:     // March
                    nDays = nDays + 31;
                    break;
                case 3:     // April
                    nDays = nDays + 30;
                    break;
                case 4:     // May
                    nDays = nDays + 31;
                    break;
                case 5:     // June
                    nDays = nDays + 30;
                    break;
                case 6:     // July
                    nDays = nDays + 31;
                    break;
                case 7:     // August
                    nDays = nDays + 31;
                    break;
                case 8:     // September
                    nDays = nDays + 30;
                    break;
                case 9:     // October
                    nDays = nDays + 31;
                    break;
                case 10:     // November
                    nDays = nDays + 30;
                    break;
                case 11:     // December
                    nDays = nDays + 31;
                    break;
            }
        }
        nDays = nDays + dDate.getDate();
        return nDays;
    }

Answer 3

If you want whole days for your student camera rental example ...

function daysBetween(first, second) {

    // Copy date parts of the timestamps, discarding the time parts.
    var one = new Date(first.getFullYear(), first.getMonth(), first.getDate());
    var two = new Date(second.getFullYear(), second.getMonth(), second.getDate());

    // Do the math.
    var millisecondsPerDay = 1000 * 60 * 60 * 24;
    var millisBetween = two.getTime() - one.getTime();
    var days = millisBetween / millisecondsPerDay;

    // Round down.
    return Math.floor(days);
}

Answer 4

To get the full days the date interval over daylight saving time changes the floor(days) must be replaced by round. Otherwise it's a very useful function.

Answer 5

I just had this problem and solved it after finding this question, so I came back to post this. This will get the total days regardless of time. And DST doesn't mess it up:

date1 = Date.UTC(date1.getFullYear(), date1.getMonth(), date1.getDate());
date2 = Date.UTC(date2.getFullYear(), date2.getMonth(), date2.getDate());
var ms = Math.abs(date1-date2);
return Math.floor(ms/1000/60/60/24); //floor should be unnecessary, but just in case

The trick is converting to a UTC date that doesn't even know about the times of the original dates.

Answer 6

Since the Julian day is effectively the number of days (and in some cases also the fraction of number of days) since a certain date, it is practically the same as a UNIX timestamp, presented differently. You can get the number of whole days since 1970 like so:

Date.prototype.getWholeDays = function () {
    return Math.floor(new Date() / 1000*60*60*24);
};

function dateDiff(startDate, endDate) {
    return endDate.getWholeDays() - startDate.getWholeDays();
}