Add new feature addBusinessDays

[codinsonn]

Should partly solve #584. Allthough it does not take holidays into consideration, I recon it might still have some value for end users.

[codinsonn]

PS: Also planning on making a PR for a getWeekDays function somewhere in the near future.

This is how I've solved the lack thereof so far:

// Get a range or number of weekdays
export const weekDays = (start: DirtyDateType, end: DirtyDateType, asNumber: boolean = false) => {
    const businessDays = eachDay(toDate(start), toDate(end)).filter(d => !isWeekend(d));
    return asNumber ? businessDays.length : businessDays;
};

Is a function like this something that could be handy in your opinion?

[kossnocorp]

I like the idea but weekday means any day, not just working days so I suggest naming it addWorkingDays.

[kossnocorp]

Update: I've figured that "business day" is more common term, so please name it addBusinessDays.

[codinsonn]

Update: I've figured that "business day" is more common term, so please name it addBusinessDays.

Updated to addBusinessDays as requested 🙌

[kossnocorp]

Thanks for the update! I see that the tests fail in America/Santiago time zone: https://travis-ci.org/date-fns/date-fns/jobs/543469770#L691

The problem that your tests operate on the DST edge (which is a lucky coincidence) and it causes an hour shift. Look how eachDayOfInterval solves this problem: https://github.com/date-fns/date-fns/blob/master/src/eachDayOfInterval/index.js#L94. However, in your case, instead of setting time to 00:00, you have to save hours from the original date and reapply in each iteration. I think this will work.

Since your function, is affected by DST, please add a DST test. See:

• https://github.com/date-fns/date-fns/blob/master/scripts/test/dst.sh
• https://github.com/date-fns/date-fns/blob/master/test/dst/eachDayOfInterval/basic.js

Also, please rebase your branch with the fresh master.

Please tell me if you need assistance!

[codinsonn]

I'm not 100% sure I follow.
I get that the DST is giving problems in some regions, but I'm still unsure of how to fix it.

More specifically, I'm unsure of:

• How to "save" hours in the function
• If I should move the failing test from ./src/addBusinessDays/test.js to ./test/dst/addBusinessDays/basic.js

PS: I'll likely only have time to get back to this in a few days.
Any help would be appreciated though.

[kossnocorp]

Alrighty, I'll proceed from here 👌

[kossnocorp]

You can see the solution for the DST problem: 03bbf4d

[kossnocorp]

It's complete.

[kossnocorp]

This PR was released as v2.0.0-alpha.32: https://gist.github.com/kossnocorp/a307a464760b405bb78ef5020a4ab136#v200-alpha32

[codinsonn]

Thanks a bunch for the help and finalisation! 🙌 I’ll try to take some time this weekend to check out how the final pieces actually connect with fixing the tests

[hugows]

Its very unexpected that this function doesn't accept negative arguments.