Scala.js: export class constructor with parameters to javascript

Question

Learning scala.js and trying to export a scala.js class to javascript like this:

@JSExport("Pt")
class Pt[T]( points: Seq[T] ) {

    @JSExport
    def y = points(1)
}

When I tried this in javascript console (Chrome):

new Pt([1,2,3])

The above throws an error: "$c_sjsr_UndefinedBehaviorError ... 1,2,3 is not an instance of scala.collection.immutable.Seq". Not sure how I can pass a Seq as parameter in javascript.

What's the trick to create a class constructors with parameters, so that it can work as both javascript library and scala library? Do I have to use js.Array? (would prefer immutable collection if possible)

I tried @JSExportAll but it doesn't work either:

@JSExportAll
class Pt[T]( points: Seq[T] ) {
    def y = points(1)
}

Then in javascript console (Chrome), I cannot even find the constructor function. It throws "ReferenceError: Pt is not defined"

I think what you have to export is a js.Array[T], within your class then it can be used as Seq[T] (probably you need to wrap it.) For constructors, you might be interested in this page. — Gábor Bakos
– Gábor Bakos, Commented Aug 2, 2016 at 9:31
Yeah, I agree that that's probably what is going on. Remember, at the JavaScript API the Scala code has to describe things using JS types, because JavaScript knows nothing about Scala types. So you pass in the mutable js.Array, then convert it to the immutable Seq for use in the Scala code... — Justin du Coeur
– Justin du Coeur, Commented Aug 2, 2016 at 11:57

gzm0 · Accepted Answer · 2016-08-03 08:54:08Z

4

You have a couple of options:

Use `js.Array` everywhere

@JSExport
class Pt[T](points: js.Array[T]) {
  def y = points(1)
}

// Scala
val pt = new Pt(js.Array(1,2,3))

// JS
var pt = new Pt([1,2,3])

Make a secondary constructor that takes a `js.Array`

class Pt[T](points: Seq[T]) {
  @JSExport
  def this(points: js.Array[T]) = this(points.toSeq)

  def y = points(1)
}

// Scala
val pt = new Pt(Seq(1,2,3))

// JS
var pt = new Pt([1,2,3])

Take a variable argument list in the constructor

@JSExport
class Pt[T](points: T*) {
  def y = points(1)
}

// Scala
val pt1 = new Pt(1,2,3)
val pt2 = new Pt(seq: _*)

// JS
var pt = new Pt(1,2,3)

answered Aug 3, 2016 at 8:54

gzm0

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1 Comment

William Ngan Over a year ago

Thank you! This is very helpful.

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Scala.js: export class constructor with parameters to javascript

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Use `js.Array` everywhere

Make a secondary constructor that takes a `js.Array`

Take a variable argument list in the constructor

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1 Answer 1

Use js.Array everywhere

Make a secondary constructor that takes a js.Array

Take a variable argument list in the constructor

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Use `js.Array` everywhere

Make a secondary constructor that takes a `js.Array`