Is it by design, that `Array.isArray()` returns `...

# javascript

[István Mészáros]

Is it by design, that Array.isArray() returns false for an instance returned by KtList.asJsReadonlyArrayView() ? I'm trying to migrate classes from Array to List but I use Array.isArray quite frequently so this a bit annoying.

I checked the JS exported source of the stdlib, and this could be fixed by replacing new Proxy(arrayView, ...) with new Proxy([], ...) here:

function createJsArrayViewWith(listSize, listGet, listSet, listDecreaseSize, listIncreaseSize) {
  var arrayView = objectCreate(protoOf(JsArrayView));
  return new Proxy(arrayView, {get: function (target, prop, receiver) {

My current workaround is to proxy the proxy:

function proxy<E>(arg: ReadonlyArray<E>) { return new Proxy([], {
  get(_target, prop: any, _receiver) {
    return arg[prop];
  },
  has(_target, prop: any) {
    return prop in arg;
  }
})}

[Artem Kobzar]

Could you please create an ticket on YouTrack for it, and I will try to change it ASAP

[István Mészáros]

Sure thing, heres the link to the issue: https://youtrack.jetbrains.com/issue/KT-69892/Array.isArray-returns-false-for-an-instance-returned-by-KtList.asReadonlyArrayView

Thanks in advance!

[Edoardo Luppi]

Note that you might face this issue using the new collections export.
https://youtrack.jetbrains.com/issue/KT-69353

In case it happens, you can add a doLast step to the link task to enhance the .d.ts file

binaries.withType<JsIrBinary>().configureEach {
  linkTask.configure {
    doLast { ... }
  }
}

[István Mészáros]

@Artem Kobzar I also posted another issue related the collections: https://youtrack.jetbrains.com/issue/KT-69928/keys-and-values-of-KtMaps-JS-view-dont-behave-as-expected

[Edoardo Luppi]

Thanks! I'm happy to see those issues reported, means people are actually using new JS features.

Devs will be less happy tho 😂

[Edoardo Luppi]

I'm still locked to 1.9.24, so I hope by 2.1 everything will be ironed out.

[István Mészáros]

I'm really happy with these improvements like the ability to use collections in exported API and the upcoming @JsStatic. And I think these issues can be fixed quickly

[István Mészáros]

BTW I'd be happy to contribute if that is possible in any way.

[Edoardo Luppi]

I think it's better to ask in the issue if opening a PR is ok first, to sync with Kotlin's devs. I've seen other people opening PRs and those be ignored for a long time.

Also, you need to know how to add JS tests to verify the compiled code.