Hey everyone :wave:, I've run into a quirky behavi...

# javascript

[ankur2037]

Hey everyone 👋,
I've run into a quirky behavior with Kotlin/JS. Curious to know if anyone has seen this before or if it's just the norm?
I've got a data class inheriting from a sealed class. When I override a field in the data class and then console.log() the instance in JS, the overridden field appears to have an obfuscated name.

@OptIn(ExperimentalJsExport::class)
@JsExport
data class Demo(override val id: String) : DemoParent()

@JsExport
sealed class DemoParent() {
    abstract val id: String
}

fun main() {
    val demo = Demo("myId")
    console.log(demo)
}

Console shows:

Demo {q5q_1: 'myId'}
   q5q_1: "myId"
   id: "myId"
   [[Prototype]]: DemoParent

Notice the id property also has this q5q_1 version? 🤔
I'm using dev.petuska.npm for npm publishing.
Has anyone come across this? Is it a Kotlin/JS issue? Or maybe something with the dev.petuska.npm plugin?

[Artem Kobzar]

Hi 👋
I've just tried your example on playground (https://pl.kotl.in/GtpDRLJbr) and realized that it's not actually a field in your object. Seems like (at least I realized it in Chrome) it also shows to you defined properties inside prototype.
For the @JsExport class in your code we generate field to store the value and getter getter function that is used in the code. But also, for JS consumption we generate a readonly (because id is val) property on prototype with a stable name.
Seems like Chrome/Node also show this property as an objects' field

[ankur2037]

So this mean that for every overridden property, they will be always to fields, one with stable name from parent (prototype) and the other one with dynamic name (from child itself).

[Artem Kobzar]

Yes, but it's only for exported classes

[Artem Kobzar]

And from parent it will be only one (from the first exported parent) and will not copy into every child class

[ankur2037]

Got it. And there is no way to supply stable name to these child class overridden fields or stop export of them ?

[Artem Kobzar]

No, unfortunately.

[ankur2037]

Thanks for the help here 🙂