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From: "Christoph M. Becker" <cmbecker69@arcor.de>
Newsgroups: comp.lang.javascript
Subject: Re: Date arithmetic
Date: Thu, 13 Nov 2014 15:27:03 +0100
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Evertjan. wrote:

> "Christoph M. Becker" <cmbecker69@arcor.de> wrote on 12 nov 2014 in 
> comp.lang.javascript:
> 
> The code I provided can be used on selected clientside and serverside 
> platforms, so please can we discuss the code:
> 
> ========================
> function dateDifference(d0, d1) {
> 
>   var msPerDay = 8.64e7;
> 
>   // make JS-dates from string parameters
>   var x0 = new Date(d0);
>   var x1 = new Date(d1);
> 
>   // set both to noon to minimize DST errors
>   x0.setHours(12,0,0);
>   x1.setHours(12,0,0);
> 
>   // substract and then round to remove DST errors
>   return Math.round( (x1 - x0) / msPerDay );
> 
> };
> =========================

In the given case (there is no time involved), I would work around any
potential DST issues by using Date.UTC().  Parsing the date strings is
slightly more complex, but the calculations should be exact (not even
Math.round() is needed).

    function daysBetween(isoDay1, isoDay2) {
        var msPerDay = 24 * 60 * 60 * 1000,
            isoExp = /^\s*(\d{4})-(\d\d)-(\d\d)\s*$/,
            parts, timestamp1, timestamp2;

        parts = isoExp.exec(isoDay1);
        timestamp1 = Date.UTC(parts[1], parts[2] - 1, parts[3]);
        parts = isoExp.exec(isoDay2);
        timestamp2 = Date.UTC(parts[1], parts[2] - 1, parts[3]);

        return Math.abs(timestamp2 - timestamp1) / msPerDay;
    }

-- 
Christoph M. Becker