I hope this is the right place to ask these questi...

# javascript

[Fleshgrinder]

I hope this is the right place to ask these questions:

1. Are there no conversion function from any kind of ArrayBuffer to a Kotlin array and/or vice-versa?
2. How do you await a Promise<S> while blocking execution? (let x = await f())

[vonox7]

@2: I would use this extension function:

suspend fun <T> Promise<T>.await() = suspendCoroutine<T> { continuation ->
  then { value -> continuation.resume(value) }

  catch { exception ->
    @Suppress("USELESS_ELVIS") // Necessary since reject can be called without parameter
    continuation.resumeWithException(exception ?: Exception("Empty promise rejection"))
  }
}

[gbaldeck]

Not sure about the first one. But for the second you are looking for Kotlin coroutines. I'm just learning them now myself. Edit: what Valentin said

[vonox7]

Edit: copied the wrong version, the snipped above is now the correct one for stable coroutines >= Kotlin 1.3

[Fleshgrinder]

Thanks, pulling in all of coroutines for a js built-in is heavy...

[Fleshgrinder]

Well, at least you don't need anything else anymore afterwards: https://kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines/kotlin.js.-promise/await.html

[Fleshgrinder]

There is no runBlocking and it is thus impossible to define a function as not being suspend. Or is there any workaround? (searching…)

[Fleshgrinder]

I give up …

[vonox7]

You can launch everywhere a new couroutine:

fun launch(block: suspend () -> Unit) {
  async(block).catch { exception -> console.error("Failed with $exception") }
}

[vonox7]

fun <T> async(block: suspend () -> T): Promise<T> = Promise { resolve, reject ->
  block.startCoroutine(object : Continuation<T> {
    override fun resumeWith(result: Result<T>) {
      if (result.isSuccess) {
        resolve(result.getOrThrow())
      } else {
        reject(result.exceptionOrNull()!!)
      }
    }

    override val context: CoroutineContext get() = EmptyCoroutineContext
  })
}

[Fleshgrinder]

I have an MPP project with a fun doSomething() and I want to have this in JS too. The doSomething does SHA-1, hence, I want to use SubtleCrypto to have a fast and proper impl. SubtleCrypto.digest returns a Promise and now I'm essentially fucked because I cannot resolve this while keeping the contract blocking for all the others.

[vonox7]

Sorry, I don’t understand you

[Fleshgrinder]

Let‘s say expect fun sha1(data: ByteArray): ByteArray is in commonMain.

We want to have actual fun sha1(data: ByteArray): ByteArray in jsMain.

We want to use https://developer.mozilla.org/en-US/docs/Web/API/SubtleCrypto/digest since it is native and tested. It returns a Promise<ArrayBuffer> (see https://developer.mozilla.org/en-US/docs/Web/API/SubtleCrypto/digest#Return_value) which is fine in theory but impossible for us here.

We cannot make an actual suspend fun unless we have an expect suspend fun, which we do not have. 😞

[Fleshgrinder]

I'd be eternaly grateful if you can think of something. I tried various things but (as written above) gave up…