JSON.stringify does not allow returning undefined

Calling JSON.stringify with undefined, or a function returns undefined in most contexts (browsers)

val x = scala.scalajs.js.JSON.stringify(())

println(s"found: $x" )

see: https://scalafiddle.io/sf/oFq7bkS/0 to reproduce.

I believe there are two directions to go, either change the return type to UndefOr[String] or document that this function may throw an exception.

[sjrd]

I agree with @gzm0 here. At the end of the day, it is a bit of a judgment call what uses of an API are considered “valid”. Very old JavaScript APIs like JSON are very permissive, often more for legacy reasons than careful design. If we always type the most permissive interpretation of those APIs, the expected, regular usages become very clunky. It becomes a trade-off.

In some cases like js.Array, we make an intentional decision to restrict the facades to “valid” use cases, for some definition of “valid” that we chose. In the case of JSON.stringify, I don’t remember it being an intentional decision when we added it, but I think that sticking to String is reasonable.

[ritschwumm]

@gzm0 good point

now, i wonder if i can make use of the type system to prevent passing invalid values to JSON.stringify…