October broken on Firefox Nightly

[fczuardi]

Steps to reproduce:

1. Download and install Firefox Nightly 40.0a1 (2015-04-29) (mac osx 10.9.5)
2. Open the demo page at http://www.gpbl.org/react-day-picker/
3. Navigate to October 2014, or October 2015 or October 2016

Expected results:

• A nice looking calendar for that month

Actual results:

• The 4th line duplicates the 3th line and then extends 6 more days missing one, example (October 2014): 12, 13, 14, 15, 16, 17, 18, 20, 21, 22, 23, 24, 25

[fczuardi]

This is a warning I get on the console when I browse to one of the broken Octobers:

"Warning: flattenChildren(...): Encountered two children with the same key, .$290. Child keys must be unique; when two children share a key, only the first child will be used."

[fczuardi]

I am trying to dig into this, the function weeks of ./CalendarUtils is returning one 8 days week for the month of october for some reason:

Array [ Array[3], Array[7], Array[8], Array[7], Array[7] ]

[fczuardi]

I wonder if this might be a daylight saving time issue, patching this CalendarUtils.js line

https://github.com/gpbl/react-day-picker/blob/master/dist/CalendarUtils.js#L22

to increase the day using:

currentDay.endOf('day').add(1, 'd');

instead of

currentDay.add(1, 'd');

fixed the "8 days week" issue (and duplicated day in a week, and duplicate key in react issues), but not the layout of the calendar yet, maybe because of a similar addition or subtractions of day in the code.

I will dig deeper and look for a related moments issue as well…

[fczuardi]

A simplified testcase:

var oct182014Plus1 = moment('2014-10-18').add(1,'d');
console.log('18 of october 2014 + 1 day', oct182014Plus1.format(), oct182014Plus1.valueOf());

On Chrome returns:

18 of october 2014 + 1 day 2014-10-19T01:00:00-02:00 1413687600000

and on Firefox:

"18 of october 2014 + 1 day" "2014-10-18T23:00:00-03:00" 1413684000000

[fczuardi]

Ok, it boils down to local date vs utc date, one possible fix is to update line #22 of CalendarUtils.js to use UTC instead of local, with:

      currentDay.utc().add(1, 'd');

[fczuardi]

I have created a pull request with a fix, please let me know if this is not the proper fix or the proper way to contribute :)

[gpbl]

@fczuardi thanks for taking care, it is indeed a weird issue. i'd like to investigate it first – maybe a problem with the nightly itself?

[fczuardi]

Yes, it might be a firefox bug, please leave an update in the related moment js issue if you figure out.

[fczuardi]

@gpbl check the comments on moment/moment#2353 to see the explanation, it is not necessarily a firefox bug since "The ECMAScript spec does not define the behavior for a local time value that falls into a DST transition", just a different implementation.

Anyways, from the moment.js folks this issue is a wontfix, they are fine living with october 18 + 1 day = october 18 since in brasilia's local time that day has 25 hours :)

As for the react-day-picker side of things, this is still a bug since it breaks the calendar layout.

[gpbl]

Hey @fczuardi thanks for the follow up. Interesting case. Will merge your PR 👍

[gpbl]

Fix published on npm as v0.8.2

[fczuardi]

Checking on the github commits historty doesn't look like the pr was merged, I will test it later on my computer to let you know if this is still happening in 0.8.2