CODEWITHSUNDEEP
scalascala.js
Bahul Jain
Bahul Jain

Reputation: 303

Creating a scala.js facade with multiple possible return types

I am trying to create a scala.js facade for an existing javascript library. This one particular function has the following signature:

def something(command: String) = js.native

Now the issue is that in the actual javascript library this method returns a String for one value of command and returns a JQuery for another value of command. I am not sure what to make the return type for this method. I was thinking of keeping it as js.Any and then the user would have to convert it to the respective type using asInstanceOf, but I think it can be handled in a better way.

Any suggestions?

Upvotes: 2

Views: 227

Answers (1)

Justin du Coeur
Justin du Coeur

Reputation: 2659

Personally, I would probably wrap this as multiple strongly-typed functions in Scala, wrapping around the specialized Strings.

For an example, see the Manifest facade that I built for Querki. That has an internal facade that just describes the literal call:

@js.native
trait ManifestFacade extends js.Object {
  @JSName("manifest")
  def manifestInternal(cmd:String, params:js.Any*):Any = js.native
}

That isn't intended for application use, though. Instead, there is a wrapper layer around that, with functions that are more precise, such as:

class ManifestCommands(manifest:ManifestFacade) {
  def manifestList():dom.Element = manifest.manifestInternal("list").asInstanceOf[dom.Element]
  def manifestGetOptions():js.Dictionary[js.Any] = manifest.manifestInternal("option").asInstanceOf[js.Dictionary[js.Any]]
  def manifestGetOption(name:String):Any = manifest.manifestInternal("option", name)
}

There is an implicit conversion from ManifestFacade to ManifestCommands. (This is oldish code; nowadays, I would write ManifestCommands as an implicit class.)

It's a bit of extra effort upfront, but this allows the application code to work at a nice, strongly-typed level, without worrying about the way the various commands are really calling a wildly polymorphic function under the hood.

Upvotes: 2

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