When exporting a kotlin interface with suspending functions im getting the following error: `Declara...

# javascript

[Andrew Reed]

When exporting a kotlin interface with suspending functions im getting the following error:
Declaration of such kind (suspend function) cant be exported to JS
How do i get around this? im currently marking my interface as external to be able to export it to JS, but how can i export a suspending function?
Here is an example:

@JsExport
@JsName("CoolInterface")
external interface CoolInterface {

    @JsName("suspendingFunc")
    suspend fun suspendingFunc(root: String): String?
}

[mbonnin]

You'll need to expose a Promise I believe

[Andrew Reed]

yes but that is tricky when this is a KMP project, so my JVM layer wants to be a suspending function

[mbonnin]

If the caller is Kotlin then you don't need JsExport ?

[mbonnin]

If the caller is JS then it doesn't know anything about suspend

[mbonnin]

Same for Swift where suspend are generated as functions with completions

[Andrew Reed]

this is a library written in KMP, supports JS and JVM targets, the interface is required to be exported as it is implemented in the consuming platform (e.g. JS and JVM)

[mbonnin]

But it's going to be implemented in Kotlin, right?

[mbonnin]

What happens if you remove @JsExport ?

[Andrew Reed]

if i dont add a jsExport, then my native JS code will not see the interface

[mbonnin]

Mmmmm the interface will be implemented in Kotlin, not JS, right?

[Andrew Reed]

no

[mbonnin]

Ah

[Andrew Reed]

yep

[Andrew Reed]

🤣

[mbonnin]

yea well I don't think that's possible

[Andrew Reed]

i was thinking something on the lines of being able to do an expect

[Andrew Reed]

but i think it wont work

[Andrew Reed]

If i use legacy, it will work, but im trying to upgrade my project to IR and 1.6

[hfhbd]

Current workaround is creating a wrapper to return the promise on JS: https://kotlinlang.slack.com/archives/C0B8L3U69/p1634577714266300

[ankushg]

If you want to implement the interface in JS/iOS, you could try to export a callback-based Interface instead, and then have a way to convert it to a suspend fun within your KMP project