When testing Kotlin 2.2.20 (currently RC-266) I've...

# webassembly

[Robert Jaros]

When testing Kotlin 2.2.20 (currently RC-266) I've noticed external classes declared in my code no longer work if there are no real classes in JS. More in thread 🧵

[Robert Jaros]

Until 2.2.0 I was using a declarations like this: https://github.com/rjaros/kilua/blob/kotlin-2.2.20/modules/kilua-tempus-dominus/src/commonMain/kotlin/dev/kilua/externals/Locales.kt#L33-L36 to simplify my code (I declared a bunch of external objects below the class definition without any additional properties declarations). This was working correctly with 2.2.0 and is still working correctly for the JS target with 2.2.20.

[Robert Jaros]

But with wasmJs target on 2.2.20 I've got a runtime error:

TempusDominusLocale is not defined
dev.kilua.externals.TempusDominusLocale_$external_class_instanceof@webpack-internal:///./kotlin/kilua-project-examples-playground.uninstantiated.mjs:13228:100
<dev.kilua:playground>.dev.kilua.externals.TempusDominusLocale_$external_class_instanceof__externalAdapter@http://localhost:3000/34442f042fcc762b1ae2.wasm:wasm-function[58947]:0x6b8e62
<dev.kilua:playground>.dev.kilua.form.time.AbstractRichDateTime.initializeTempusDominus@http://localhost:3000/34442f042fcc762b1ae2.wasm:wasm-function[59599]:0x6c6c27

[Robert Jaros]

The message is correct, there is no TempusDominusLocale class in JS.

[Robert Jaros]

But I can't find an issue in the changelog.

[Robert Jaros]

And yes, I can change class to interface and declare overrides for the properties in all my external objects to fix the problem (it's just a bit more code).

[Robert Jaros]

Shouldn't JS interop work the same with JS and wasmJS targets?

[turansky]

Looks like expected error 🙂

[turansky]

Probably issue, which you search, was reported by Robert Jaros - KT-76509 🙂

[turansky]

and declare overrides for the properties in all my external objects

You can declare "mixin" to avoid redundant overrides

[turansky]

Mixin example

[Robert Jaros]

Love adding more magic suppressions to my code 😜

[turansky]

Mixin issue will be helpful 😉

[Robert Jaros]

@JsExternalInheritorsOnly what does this do?

[turansky]

Limit inheritance

[turansky]

It won't be possible to declare non-external inheritor

[Robert Jaros]

It's used by some compiler plugin?

[turansky]

It's part of Kotlin/JS

[turansky]

It will check it

[turansky]

Original - https://kotlinlang.org/api/core/kotlin-stdlib/kotlin.js/-js-external-inheritors-only/

[Robert Jaros]

And is it required for mixin? Or just added for some other reasons.

[turansky]

In case of real mixins your nearest child should be external

[Robert Jaros]

Works perfect. Thanks once again!

[turansky]

In wrappers we mark ~50% of mixins as "external only"

[turansky]

Other part we will mark later as "no direct inheritors outside the project"

[turansky]

With help of this annotation

[turansky]

100+ mixins in browser 😉
Looks like issue