getDayOfWeekCode in date_utils has incorrect behavior.

[ymmt07039]

Describe the bug
getDayOfWeekCode in date_utils returns an incorrect value.
It is expected to return day-of-week codes such as sun, mon, tue, but currently returns the day of year month.

Expected behavior
getDayOfWeekCode should return lowercase day-of-week codes such as sun, mon, tue (see #800).

Additional context

• The current behavior occurs because the format ddd is used.
• In date-fns, the correct format for day of week is eee.
• The locale needs to be fixed to en, and the result needs to be converted to lowercase.
• Reference code:
  

  react-datepicker/src/date_utils.ts

  Lines 592 to 594 in 548a1f3

  	export function getDayOfWeekCode(day: Date, locale?: Locale): string {
  	return formatDate(day, "ddd", locale);
  	}

• date-fns format document:
  https://date-fns.org/docs/format

[balajis-qb]

Hi,

Actually the code ddd is correct here, because we're just using it to add the dynamic class names for the month days. But the function name and it's documentation is a bit-confusing. I'll update that.

[ymmt07039]

Wasn't this feature originally implemented to apply style to days of the week? #800

I suspect it was caused by date-fns v2 breaking changes. (v1 was ddd)
https://github.com/date-fns/date-fns/blob/main/CHANGELOG.md#200---2019-08-20

[balajis-qb]

Hi,

Thanks for the catch. Yes, as you mentioned initially getDayOfWeekCode was implemented to return day-of-week codes such as sun, mon, tue.

But later when the date_utils module was refactored due to the removal of moment.js. As a part of that PR only we installed date_utils@2.0.0-alpha.23. Since that time itself it was implemented as ddd (which was supposed to be EEE as we were using date-fns v2.0.0-alpha.23). As it was implemented long back, many tests were written on the days to assert for the codes like 001, 002, 003, etc. So, we can't remove that class name as it will break many tests.

I'll add both the day-of-week codes class names to the day component along with the day-of-month codes class name.

[ymmt07039]

I understand. Thank you!