Throw String in Kotlin/JS leads to ClassCastException

[ilgonmic]

Describe the bug

https://youtrack.jetbrains.com/issue/KT-72174/Kotlin-JS-Coroutines-throwing-JS-string-does-not-stop-the-job

JavaScript allows to throw strings, but it leads to ClassCastException is thrown in kotlinx-coroutines-core
Looks createCauseException is the root cause of ClassCastException , String is not Throwable so it is trying to be cast to ParentJob

kotlinx.coroutines/kotlinx-coroutines-core/common/src/JobSupport.kt

Lines 748 to 752 in 6c6df2b

	// cause is Throwable or ParentJob when cancelChild was invoked
	private fun createCauseException(cause: Any?): Throwable = when (cause) {
	is Throwable? -> cause ?: defaultCancellationException()
	else -> (cause as ParentJob).getChildJobCancellationCause()
	}

Provide a Reproducer

class TestClient2 {
    @Test
    fun testThrowString() = runTest {
        val job = launch {
            println("throwing a JS string")
            throw IllegalStateException("EMPTY") //In JS everything can be thrown, even a String!
            println("not executed....")
        }

        println("waiting for job")
        job.join()
    }
}

[Aditys018]

Instead of assuming non-Throwable values are ParentJob
We can wrap them in an IllegalStateException with a descriptive message
This maintains type safety while handling JavaScript's flexible throwing behavior
( LMK if this approach is correct I'd love to work on it )

[dkhalanskyjb]

Unfortunately, I see no way of fixing this on our side. To wrap an exception, you first have to catch it somehow, and I didn't succeed in doing that without writing custom js("") blocks, and certainly not in the common code of our multiplatform library. I opened an issue for Kotlin/JS: https://youtrack.jetbrains.com/issue/KT-73710/No-way-to-catch-every-JS-error-in-common-code UPD: catch (e: dynamic) does work in JS without custom js("") blocks, but this, too, doesn't compile in common code.