Days between function returning odd answer with many decimal places

Question

I have this function on my calculator that is meant to determine the number of dates between two days:

    function DaysBetween(str1, str2) {
    var date1 = str1;
    var date2 = str2;

    diffDays = (new Date(date2).getTime() - new Date(date1).getTime())/(1000 * 60 * 60 * 24);

    if (diffDays == 0) {
        diffDays = 1;
    }

    return diffDays;
}

but when I put in the values of '10/10/2019', '11/13/2019' it gives me a strange output of 34.041666666666664

here is a fiddle:

function DaysBetween(str1, str2) {
    var date1 = '10/10/2019';
    var date2 = '11/13/2019';

    diffDays = (new Date(date2).getTime() - new Date(date1).getTime())/(1000 * 60 * 60 * 24);
    
    if (diffDays == 0) {
     diffDays = 1;
    }

    console.log (diffDays);
}

<button onclick="DaysBetween()">
Test!
</button>

Can someone help me fix this? Thanks.

Because Daylight Saving Time ends on November 3, so there's an extra hour on that day. — Barmar, Oct 08 '19 at 16:03
You would likely do better to parse the strings to their year, month and day components then simply do `(Date.UTC(y0, m0-1, d0) - Date.UTC(y1, m1-1, d1))/8.64e7`. UTC days are always 24 hours long so aren't affected by daylight saving. — RobG, Oct 09 '19 at 12:48

Mathieu Gemard · Answer 1 · 2019-10-09T13:57:18.260

-1

You need to use Math.round()

function DaysBetween(date1, date2) {
    diffDays = (new Date(date2).getTime() - new Date(date1).getTime())/(1000 * 60 * 60 * 24);
    console.log (Math.round(diffDays));
}

DaysBetween('10/10/2019', '11/13/2019')

34

edited Oct 09 '19 at 13:57

answered Oct 08 '19 at 16:04

Mathieu Gemard

514
7
11

1

`Math.round()` would be better. `ceil()` will add a whole day even though it was just an extra hour. – Barmar Oct 08 '19 at 16:05
The correct answer should be `34`, not `35`. – Barmar Oct 08 '19 at 16:06

Days between function returning odd answer with many decimal places

1 Answers1