Scala.js convert Scala function to JS function

Question

I know that implicit conversions are available for js.FunctionN <–> scala.FunctionN. However, if I work with libraries in dynamic fashion (without typed facade), they won't help me, because the compiler obviously doesn't know that I need a conversion. For example, if a JS code expects a JS Array with a string and a function as an input -- something like

['Hello world', function ($x, $y) {
    console.log($x + $y)
}],

, I can't create it in Scala like this:

    val a: js.Array[Any] = js.Array(
      "Hello world",
      (x: Int, y: Int) => {console.log(x + y)}
    )
  )

Because Scala function will not be converted to JS function. Does there exist some explicit conversion method for that, similar to toJSArray for mutable Seq? I've checked that asInstanceOf[js.Function] doesn't work.

Justin du Coeur · Accepted Answer · 2016-09-01 15:28:14Z

5

asInstanceOf doesn't work because that is basically saying "this function is already a js.Function", which isn't true. But this does usually convert correctly if you give it an explicit type ascription, like this (haven't tried compiling but should be roughly correct):

val a: js.Array[Any] = js.Array(
  "Hello world",
  { (x: Int, y: Int) => {console.log(x + y)} }:js.Function2[Int, Int, Unit]
)

It's a bit more boilerplate, but that's always the cost of going without facades...

answered Sep 1, 2016 at 15:28

Justin du Coeur

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1 Comment

sjrd Over a year ago

You can make it less boilerplaty by ascribing as : js.Function rather than the js.Function2[...] verbose thing. But otherwise, yes, that's pretty much what you have to do.

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