add `Instant -> JSDate`

[coot]

The purescript-now library provides a way to get Instant. The only way to get JSDate I can find is through DateTime, but this is a long walk ;). We could solve it either by

• adding an effect in now livbrary to get an js date
• or add a function Instant -> JSDate

or both :)

[chexxor]

This is really needed. I've struggled to get a JSDate value for the current time several times - it's ridiculously hard problem to solve in PS.

[garyb]

Can I ask why you need the JSDate for rather than a Date / DateTime?

It was left out on purpose, because JSDate is gross and should be avoided if at all possible. 😉

[chexxor]

I've decided that the browser part of my app is best to use JSDate everywhere, because that app interacts with lots of JS libraries, and they all use JSDate. I need to do simple stuff like pre-fill a datetime-input with the current time, or one a week from now.

A related note: I'd prefer to not ship any DateTime libraries to the browser due to my policy. To do that, then, would require adding an FFI function to this library like foreign import currentJsDate :: Eff _ JSDate.