PlainDate.dayOfWeek not adhering to the standard

[wundersolutions-juanjo]

In the current 0.2.0 version of the polyfill, PlainDate.dayOfWeek is not returning the correct value for ISO 8601 calendars

From the current docs on PlainDate,

The dayOfWeek read-only property gives the weekday number that the date falls on. For the ISO 8601 calendar, the weekday number is defined as in the ISO 8601 standard: a value between 1 and 7, inclusive, with Monday being 1, and Sunday 7. For an overview, see ISO 8601 on Wikipedia.

Usage example:

date = Temporal.PlainDate.from('2006-08-24');
['MON', 'TUE', 'WED', 'THU', 'FRI', 'SAT', 'SUN'][date.dayOfWeek - 1]; // => 'THU'

Testing that on a website using the https://cdn.jsdelivr.net/npm/[email protected]/global.min.js polyfill results on dates being one day off

[digaus]

Just had same observation. Day of week is not returning correct value:

Would be nice if this could get a hotfix

[digaus]

my current workarround:

const dayIntl: Intl.DateTimeFormat = new Intl.DateTimeFormat('en-GB', { weekday: 'short' } as Intl.DateTimeFormatOptions);
const day: 'Sun' | 'Mon' | 'Tue' | 'Wed' | 'Thu' | 'Fri'| 'Sat' =  dayIntl.format(temporalDate) as 'Sun' | 'Mon' | 'Tue' | 'Wed' | 'Thu' | 'Fri'| 'Sat';
return [ '', 'Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat', 'Sun' ].indexOf(day);

[arshaw]

I see what's going on here. The code is internally leveraging a zoned Date method (.getDay()) when it shouldn't be. This gives eradic results based on the current user's timezone. I'll get this fixed+released today.

[arshaw]

This is fixed in v0.2.1

Turns out I was incorrectly leveraging the timezone-sensitive Date::getDay() AND I had an off-by-one error when computing days-of-week, and the two bugs cancelled each other out for my particular timezone and the time of day I normally work, so I never experienced the bug (nor my CI). Fun.

[arshaw]

@digaus and @wundersolutions-juanjo could you kindly check to see if things work in your timezone (even tho timezone should not matter)

[digaus]

Yeah timezone should not matter but I can confirm, that it works now correctly with dayOfWeek

[wundersolutions-juanjo]

Looks good, both for #26 and #27, thank you very much!