Cannot select the day on which daylight savings starts

[davideaves]

Daylight savings starts on 27-Sep-2015 this year in New Zealand. When attempting to select this date by clicking on it in the datepicker the previous day is selected and highlighted instead. Selecting any other date works fine. The same behaviour is exhibited on the demo page.

The problem occurs in this code in the setTime() function:

var newDate = new Date(tempDate.getTime() + (tempDate.getTimezoneOffset() * 60000));

Replacing this with the following code resolves the issue for us:

var newDate = new Date(tempDate.getUTCFullYear(), tempDate.getUTCMonth(), tempDate.getUTCDate(), tempDate.getUTCHours(), tempDate.getUTCMinutes(), tempDate.getUTCSeconds(), tempDate.getUTCMilliseconds());

I note that getUTCTime() also uses Date.getTimezoneOffset() to adjust a date to UTC, but I'm unsure if this is a problem in that context. I haven't got my head around what it is doing and the picker seems to be behaving correctly without modifying getUTCTime().

Additional background:

New Zealand is +12 hours from UTC, or +13 hours during daylight savings. When selecting 27-Sep-2015 in the unmodified setTime():
unixDate is 1443312000000
tempDate is Sun Sep 27 2015 13:00:00 GMT+1300 (New Zealand Daylight Time)
newDate is Sat Sep 26 2015 23:00:00 GMT+1200 (New Zealand Standard Time)

newDate should instead be Sun Sep 27 2015 00:00:00 GMT+1200 (New Zealand Standard Time)

Thanks!

[dalelotts]

Thanks for the info. I'm not able to reproduce this problem with US daylight savings time - can you please create a test that reproduces this problem on the CI server?

[davideaves]

Hi - I'm unsure how I could create a test for this as it depends on the timezone of the environment in which the test is executed. Also I'm not very familiar with JavaScript testing!

Here is what I have observed from further investigation...

It is a problem for us in New Zealand because in our timezone ("(UTC+12:00) Auckland, Wellington") the conversion of tempDate to newDate crosses a daylight savings changeover. The timezone offset for tempDate (27-Sep-2015 13:00) is 13 hours while for newDate it is 12 hours.

Using date + date.getTimeZoneOffset() to create a date representing the datetime in UTC won't work in the general case for this reason. It happens to work in the US as the timezones are behind UTC so the conversion never crosses a daylight savings changeover. I expect any location that observes daylight savings and is more than a couple of hours ahead of UTC will experience the problem (assuming daylight savings always starts at 2am local). I tested this for Australia by setting my timezone to "(UTC+10:00) Canberra, Melbourne, Sydney" and encountered the same issue. Note not all Australian states observe daylight savings.

The code I proposed avoids this issue by getting the browser to perform the conversion instead.

I hope this helps. Dave

[dalelotts]

I understand your explanation, however, without a failing test I don't have the time to dig into this defect. Anyone willing to pitch in an help work through this issue?

[defmonk0]

JavaScript uses your local machine's time for its date functions. If you simply open the time settings on your machine and set your TZ to UTC+12: Auckland / Wellington, you should be able to reproduce it easily. I just did on the demo page.

[dalelotts]

I understand that, I looked into a bit, but at the moment I don't have time to solve it. I can't make any progress or accept a PR without a test - wanna send me a failing test?

[defmonk0]

Ah. Sorry. I don't have karma set up on my machine, and only commented in passing since I just started using this on a project at work. :P

[joelatty]

This happens for us ((UTC+10:00) Sydney Australia) on the 4th of October, clicking on the 4th populates the input with the 3rd and does not select any column on the calendar.

[dalelotts]

I completely believe that this is an issue - if someone could just get a failing test written I can find a fix - or a PR with a test and fix already in place would be great! - I've spent a few hours working on it and so far I am not able to reproduce it - sorry, if those effected by this defect cannot be bothered to work on it, why should I?