When porting JS code to WebAssembly, what strategy...

# webassembly

[Tóth István Zoltán]

When porting JS code to WebAssembly, what strategy should I follow for functions not exposed by kotlinx.browser?

For example, this works for JS but I can't figure out how to do this in WASM.

private suspend fun Blob.asByteArray(): ByteArray {
        //<https://developer.mozilla.org/en-US/docs/Web/API/Blob/arrayBuffer>
        val buffer = asDynamic().arrayBuffer() as Promise<ArrayBuffer>
        return Int8Array(buffer.await()).unsafeCast<ByteArray>()
    }

[Robert Jaros]

You can use js.reflect.Reflect for pseudo-dynamic code if you use kotlin-wrappers library instead of stdlib browser apis.

[Robert Jaros]

I use these functions https://github.com/rjaros/kilua/blob/main/kilua/src/commonMain/kotlin/dev/kilua/utils/JavaScript.kt#L51-L63

[Robert Jaros]

To allow this kind of code: https://kilua.gitbook.io/kilua-guide/2.-frontend-development-guide/interoperability-with-javascript#dynamic-typing

[Robert Jaros]

If you write wasmJs code directly you can also just use js() functions for most dynamic things.

[Tóth István Zoltán]

This is a great resource, thank you.

[Robert Jaros]

If you write common (or web shared) code - you may need some expect/actuals

[Tóth István Zoltán]

I rarely touch Js, but have a few cases where it is unavoidable.

[Tóth István Zoltán]

Yes, I already have all platform-dependent stuff in expect/actuals.

[Todd]

I had very similar code. This is what I ended up with

fun Blob.arrayBuffer(): Promise<ArrayBuffer> = arrayBuffer(this)

private fun arrayBuffer(blob: Blob): Promise<ArrayBuffer> = js("blob.arrayBuffer()")

fun ArrayBuffer.toByteArray(): ByteArray =
    Int8Array(buffer = this, 0, byteLength).toByteArray()

Then I was using it like

blob.arrayBuffer().await<ArrayBuffer>().toByteArray()

Only problem is it requires a copy from Int8Array toByteArray. There's might be a way to not need the copy but I haven't spent any extra time on it yet.