How does Scala.js deal with inconsistent browser APIs and type safety? Does it just include all of core-js and hope for the best?
Scala.js lets you require any npm modules, so you can `require()` any JS polyfills you want just like you would do if writing JS code by yourself.
`eventTgt.addEventListener('whatever', fn, true)`
vs
`eventTgt.addEventListener('whatever', fn, { passive: true })`
Does it just allow 'Any' for the type of the third param and thus somewhat punt on type safety at the browser API boundary or is there some attempt at defining an algebraic type for that param?
Or as another example, how would it handle the object passed to `fn` above, presumably some sort of event type, having different properties in different browsers?
But Scala.js doesn't force the standard typings on you. If you prefer another strategy, you can write your own types for the browser. You could use overloads in your example above.
That wouldn't prevent you from using the wrong overload on the wrong browser at the type system level, though, obviously. Doing so might be possible if you're willing to go very far with Scala's path-dependent types, but I won't go into details here. Scala.js users tend to prefer the earlier solutions.
You define types for everything.