Javascript dates: what is the best way to deal with Daylight Savings Time?

In a previous question I wrote about a javascript date fu开发者_Go百科nction that was mysteriously stopping on 11/07/101. Thanks to the stackoverflow users I was told my problem is Daylight Savings Time. Javascript date, is this my error or did I find a bug?

So my last question on this is what is the recommended approach in Javascript to deal with Daylight Savings Time?

Is http://code.google.com/p/datejs/ the best approach to solve this?

---

The best way is not to deal with DST. Use the UTC methods and you won't have to worry about crossing a DST boundary, or any other timezone discontinuity (locale timezone rules can change for more reasons than just DST).

var timestamp= Date.UTC(2010, 10-1, 31, 0, 0, 0); // zero-based month: 9->october
var nextday= new Date(timestamp+86400000); // add one day
var ymd= [
    nextday.getUTCFullYear(),
    nextday.getUTCMonth()+1, // zero-based month
    nextday.getUTCDate()
].join('-');
alert(ymd); // 2010-11-1

If the above had been done with new Date(2010, ...) and getDate() etc, it'd return 2010-10-31, the day add failing due to the DST change (in my region, anyway).

It is a pity that the ‘default’ most-obvious methods in Date are about local time, especially since JavaScript provides so very little context to scripts on what ‘local time’ actually is. UTC is a more stable proposition.

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Use Date.setHours(hour,min,sec,millisec) to set the hour default to noon: Date.setHours(11); (view reference)

24 hours after noon on a day is guaranteed to be the next day, though on daylight savings time days it will be one hour off (which doesn't change the result in your script at all).

---

I was in a situation where I needed the date in the local time zone, i was doing a lot of adding and subtracting days via time stamps, some time later DST gave me issues, I made a function to add days to a time stamp and check if the time zone changed cause of DST
Heres is my scratchpad test:

function timeToHuman(stamp) {
    var monthNames = ["January", "February", "March", "April", "May", "June",
            "July", "August", "September", "October", "November", "December"],
        date = new Date(stamp*1000),
        month = monthNames[date.getMonth()],
        day = date.getDate(),
        year = date.getFullYear(),
        hour = date.getHours(),
        min = date.getMinutes(),
        amp;
    if(hour>11){
        hour -= 12;
        amp = "PM";
    }
    else
        amp="AM";
    hour = hour==0?12:hour;
    min = min<10?"0"+min:min;
    return month + " " + day + ", " + year + " @ " +  hour + ":" + min + " " + amp +// Month/Day /Year
        " || "+year+"/"+(date.getMonth()+1)+"/"+day+ " @ " +  date.getHours() + ":" + min;// Year/Month/Day
}
function addDays(stamp,days){//stamp = new Date().getTime()/1000
    var sec=days*86400,
        B4=new Date(stamp*1000).getTimezoneOffset(),
        A=new Date((stamp+sec)*1000).getTimezoneOffset();
    if(B4!=A){// DST correction
        A=(A-B4)*60;
        console.log('DST adjust by:',A,'seconds');
        sec+=A;
    }
    return stamp+sec;
}
var sample=[
         Math.floor(new Date('Sun Mar 10 2018 11:38:59 GMT-0500 (EDT)').getTime()/1000),// day before DST change
         Math.floor(new Date('Sun Mar 11 2018 11:38:59 GMT-0400 (EDT)').getTime()/1000),// day after DST change
         Math.floor(new Date('Sun Nov 3 2018 11:38:59 GMT-0400 (EDT)').getTime()/1000),// day before DST change
         Math.floor(new Date('Sun Nov 4 2018 11:38:59 GMT-0500 (EDT)').getTime()/1000)// day after DST change
      ]
    date=[];
for(i in sample){
    i=parseInt(i,10);
  date.push('Without DST Detection, Part '+(i+1));
  date.push('\t'+timeToHuman(sample[i]+2*86400));
  date.push('\t'+timeToHuman(sample[i]+1*86400));
  date.push('\t'+timeToHuman(sample[i]));
  date.push('\t'+timeToHuman(sample[i]+-1*86400));
  date.push('\t'+timeToHuman(sample[i]+-2*86400));
  date.push('\t'+timeToHuman(sample[i]+-3*86400));
  date.push('With DST Detection, Part '+(i+1));
  date.push('\t'+timeToHuman(addDays(sample[i],2)));
  date.push('\t'+timeToHuman(addDays(sample[i],1)));
  date.push('\t'+timeToHuman(sample[i]));
  date.push('\t'+timeToHuman(addDays(sample[i],-1)));
  date.push('\t'+timeToHuman(addDays(sample[i],-2)));
  date.push('\t'+timeToHuman(addDays(sample[i],-3)));
}
date.join('\n');

/*
Without DST Detection, Part 1
    March 12, 2018 @ 12:38 PM || 2018/3/12 @ 12:38
    March 11, 2018 @ 12:38 PM || 2018/3/11 @ 12:38
    March 10, 2018 @ 11:38 AM || 2018/3/10 @ 11:38
    March 9, 2018 @ 11:38 AM || 2018/3/9 @ 11:38
    March 8, 2018 @ 11:38 AM || 2018/3/8 @ 11:38
    March 7, 2018 @ 11:38 AM || 2018/3/7 @ 11:38
With DST Detection, Part 1
    March 12, 2018 @ 11:38 AM || 2018/3/12 @ 11:38
    March 11, 2018 @ 11:38 AM || 2018/3/11 @ 11:38
    March 10, 2018 @ 11:38 AM || 2018/3/10 @ 11:38
    March 9, 2018 @ 11:38 AM || 2018/3/9 @ 11:38
    March 8, 2018 @ 11:38 AM || 2018/3/8 @ 11:38
    March 7, 2018 @ 11:38 AM || 2018/3/7 @ 11:38
Without DST Detection, Part 2
    March 13, 2018 @ 11:38 AM || 2018/3/13 @ 11:38
    March 12, 2018 @ 11:38 AM || 2018/3/12 @ 11:38
    March 11, 2018 @ 11:38 AM || 2018/3/11 @ 11:38
    March 10, 2018 @ 10:38 AM || 2018/3/10 @ 10:38
    March 9, 2018 @ 10:38 AM || 2018/3/9 @ 10:38
    March 8, 2018 @ 10:38 AM || 2018/3/8 @ 10:38
With DST Detection, Part 2
    March 13, 2018 @ 11:38 AM || 2018/3/13 @ 11:38
    March 12, 2018 @ 11:38 AM || 2018/3/12 @ 11:38
    March 11, 2018 @ 11:38 AM || 2018/3/11 @ 11:38
    March 10, 2018 @ 11:38 AM || 2018/3/10 @ 11:38
    March 9, 2018 @ 11:38 AM || 2018/3/9 @ 11:38
    March 8, 2018 @ 11:38 AM || 2018/3/8 @ 11:38
Without DST Detection, Part 3
    November 5, 2018 @ 10:38 AM || 2018/11/5 @ 10:38
    November 4, 2018 @ 10:38 AM || 2018/11/4 @ 10:38
    November 3, 2018 @ 11:38 AM || 2018/11/3 @ 11:38
    November 2, 2018 @ 11:38 AM || 2018/11/2 @ 11:38
    November 1, 2018 @ 11:38 AM || 2018/11/1 @ 11:38
    October 31, 2018 @ 11:38 AM || 2018/10/31 @ 11:38
With DST Detection, Part 3
    November 5, 2018 @ 11:38 AM || 2018/11/5 @ 11:38
    November 4, 2018 @ 11:38 AM || 2018/11/4 @ 11:38
    November 3, 2018 @ 11:38 AM || 2018/11/3 @ 11:38
    November 2, 2018 @ 11:38 AM || 2018/11/2 @ 11:38
    November 1, 2018 @ 11:38 AM || 2018/11/1 @ 11:38
    October 31, 2018 @ 11:38 AM || 2018/10/31 @ 11:38
Without DST Detection, Part 4
    November 6, 2018 @ 11:38 AM || 2018/11/6 @ 11:38
    November 5, 2018 @ 11:38 AM || 2018/11/5 @ 11:38
    November 4, 2018 @ 11:38 AM || 2018/11/4 @ 11:38
    November 3, 2018 @ 12:38 PM || 2018/11/3 @ 12:38
    November 2, 2018 @ 12:38 PM || 2018/11/2 @ 12:38
    November 1, 2018 @ 12:38 PM || 2018/11/1 @ 12:38
With DST Detection, Part 4
    November 6, 2018 @ 11:38 AM || 2018/11/6 @ 11:38
    November 5, 2018 @ 11:38 AM || 2018/11/5 @ 11:38
    November 4, 2018 @ 11:38 AM || 2018/11/4 @ 11:38
    November 3, 2018 @ 11:38 AM || 2018/11/3 @ 11:38
    November 2, 2018 @ 11:38 AM || 2018/11/2 @ 11:38
    November 1, 2018 @ 11:38 AM || 2018/11/1 @ 11:38
*/