We have been facing a runtime issue since our upgr...

# javascript

[Mathieu Côté]

We have been facing a runtime issue since our upgrade to KMP 2.0.0 where some of our `addEventListener`/`removeEventListener` that are coming from an external definition (IMA SDK or FreeWheel SDK mapping) are removed at transpilation from Kotlin to JS and replaced by a throwLinkageError with message:

Function 'addEventListener' can not be called: No function found for symbol 'googleima/Google.Ima.AdsLoader.addEventListener|addEventListener(kotlin.String;kotlin.Function1<kotlin.Nothing?,kotlin.Unit>;kotlin.Boolean){}[0]'

It only occurs on transpilation following code modification within the class that uses the external definition mapping, and disappear following these 2 steps: a clean up (gradle intensifies clean and a removal of the kotlin-js-store folders) and a simple new line added to the current code base.

It is very strange, we cannot for the love of god isolate it to a simple test projet, it only do that within our huge code base. Any idea if this is known or if there is a possible workaround?

P.S.: attached more details in 🧵 👉

[Mathieu Côté]

External definition of IMA SDK:

package googleima

@JsName("google")
external object Google {
    @JsName("ima")
    object Ima {
        class AdsRequest {
            var adTagUrl: String?
            var vastLoadTimeout: Double?
            fun setAdWillAutoPlay(value: Boolean)
            fun setAdWillPlayMuted(value: Boolean)
        }

        class AdsManager {
            fun addEventListener(event: String, callback: (event: dynamic) -> Unit, useCapture: Boolean = definedExternally)
            fun removeEventListener(event: String, callback: (event: dynamic) -> Unit)
        }
    }
}

[Mathieu Côté]

Screenshot 2024-09-05 at 4.41.14 PM.png,Screenshot 2024-09-05 at 4.45.14 PM.png

[Mathieu Côté]

Screenshot 2024-09-09 at 8.41.12 AM.png

[Mathieu Côté]

Code that uses the definitions:

private var onAdStartedReference: ((event: Google.Ima.AdEvent) -> Unit)? = null

    private fun setUpAdsManagerEventListeners(adsManager: Google.Ima.AdsManager) {
        onAdStartedReference = { onAdStarted(it) }

        adsManager.addEventListener(Google.Ima.AdEvent.Type.STARTED, onAdStartedReference!!)
    }

    private fun removeAdsManagerEventListeners(adsManager: Google.Ima.AdsManager) {
        onAdStartedReference?.let { adsManager.removeEventListener(Google.Ima.AdEvent.Type.STARTED, it) }
    }

    private fun onAdStarted(event: Google.Ima.AdEvent) {
    }

[Edoardo Luppi]

First thing I'd do is upgrade to 2.0.20, and verify if it still happens.

[Mathieu Côté]

Good point, will do this.

[turansky]

Pill - remove dynamic usage from callbacks 😉

[turansky]

And it's common recommendation - don't use dynamic in externals.
In most cases Any? is what you need instead.

[Mathieu Côté]

Really? We been using dynamic all over the place since the beginning of our project, 3 years ago, never had an issue with that.

[Edoardo Luppi]

I mean it's not an issue per se. It's just that Any is a proper type, dynamic is not.

That said, dynamic doesn't introduce type checks, and you'll never deal with class cast exceptions, so it definitely has its use cases.

[Mathieu Côté]

Alright! Thats good information! We will adapt and look into using any? in that particular case, and advise for the rest.

[Edoardo Luppi]

Better not go around fixing what's not broken. Start introducing it only for new externals.

[Mathieu Côté]

Yep, thats what we will do!

[Mathieu Côté]

What is the risk of a cast from any to an external definition event type? Shall I protect myself everytime with a try/catch?
i.e:

private fun onAdError(event: Any) {
   val errorEvent = event as Google.Ima.AdErrorEvent
}

[Edoardo Luppi]

Not needed.
But, can event be better typed, or is Any the only way to do it?

[Mathieu Côté]

Well, depends on the use case, but for those particular add/remove event listeners, the event is dynamic and can receive different object types. Example from FreeWheel:

private var onFreeWheelRequestCompleteReference: ((event: FreeWheel.SDK.RequestCompleteEvent) -> Unit)? = null
    private var onFreeWheelSlotStartedReference: ((event: FreeWheel.SDK.SlotEvent) -> Unit)? = null
    private var onFreeWheelSlotEndedReference: ((event: FreeWheel.SDK.SlotEvent) -> Unit)? = null

Because of this, I was using dynamic in the external definition. Using Any now, forces us to do the cast as mentioned above.

These 2 types are objects like this:

object RequestCompleteEvent {
                val type: String
                val target: Context
                val success: Boolean
            }

            object SlotEvent {
                val type: String
                val target: Context
                val slot: Slot
            }

[Edoardo Luppi]

So, where specifically is onAdError called?

[Mathieu Côté]

onAdError was actually from our Google IMA implementation. Im currently doing both as we speak, but FreeWheel was easier to explain 😉

[Mathieu Côté]

On IMA SDK, these are the 2 types that can be sent as event from the addEventListener callback:

object AdErrorEvent {
            fun getError(): AdError
            fun getUserRequestContext(): Any
        }
        object AdEvent {
            val type: String
            fun getAd(): Ad?
            fun getAdData(): AdData?
        }

[Edoardo Luppi]

Seems quite a complex scenario.
I guess the best advice I can give you is to try to split up types. Use function overloads and cast at the very source of the event if you receive an "any"-like object

[Edoardo Luppi]

Are you writing externals manually or translating them from TypeScript?

[Edoardo Luppi]

I've found https://github.com/alugha/typed-ima-sdk, which could be a good start to generate the external types. Not sure how up to date it is.

[turansky]

FAQ for externals

[Edoardo Luppi]

Since that library uses many enums, Seskar could also be handy.

[Mathieu Côté]

Good point on the overload, I missed that as a possible approach!

[Mathieu Côté]

💯 on the method overloads, that was exactly it, instead of Any or dynamic. Works wonder. Thanks guys, much appreciated. Since the issue is unpredictable, I will ping back if we encounter it again following these changes.