React-datepicker: Replace `tether` with `popper` package for calendar popups

[tohjustin]

This is a follow up from the discussion at #899.

Since the project status for Tether is up in the air, Popper.js seems like a better alternative & even the maintainers of Tether recommended it.

[tohjustin]

@alex-shamshurin @martijnrusschen @rafeememon Would be great if you guy can assign this issue to me =)

[rafeememon]

I don't think we use assignments in this repo but you're free to start working on this!

[FezVrasta]

Take a look at react-popper for a battle tested React integration with Popper.js

[tohjustin]

@FezVrasta Thanks for the heads up, will look at it over the weekend!

[alex-shamshurin]

Waiting for PR to test it!

[tohjustin]

@alex-shamshurin @rafeememon Just a quick question, do you think we should use popper.js directly or just use react-popper? Cause I'm a bit skeptical about how 'battle tested' this wrapper module is when there's no form of testing implemented =/

Also, let's say we're using react-popper and there's some bug in popper.js or react-popper itself, won't we have to wait for the guys w/ the react-popper to fix the stuff before we can update our dependencies & ship the fix on our end?

[FezVrasta]

I use react-popper in production and it works wonderfully.

I know there's an issue open to add tests, rather than create a new project consider add tests to the existing one maybe?

Also, react-popper doesn't lock you to a specific version,this means you can update Popper.js independently.

[tohjustin]

@FezVrasta Thanks for the quick reply! Didn't realize that you're also the creator of popper.js, I guess I shouldn't be worried about this issue then xD

[tohjustin]

@alex-shamshurin @rafeememon Popper.js uses a different way of specifying the behavior of the popups & there's some differences in functionality...

Do you guys intend to maintain the same API & all tether related props? (classPrefix, attachment, targetAttachment, targetOffset, renderElementTo, constraints)