Common interoperability between Kotlin arrays and Js typed arrays

[zibet27]

Is your feature request related to a problem? Please describe.

I would like to have a common interoperability methods to map between Kotlin arrays and Js Typed Arrays in both Js and WasmJs targets.

Describe the solution you'd like
Example methods:

• ByteArray.toInt8Array()
• UByteArray.toUint8Array()
• IntArray.toInt32Array()
• FloatArray.toFloat32Array()
  ...
  and another way:
• Int8Array.toByteArray()
• UintArray.toUByteArray()
  ...

[mipastgt]

A possible implementation for the ByteArray case might look like this today:

import js.buffer.ArrayBuffer
import js.core.JsPrimitives.toByte
import js.core.JsPrimitives.toJsByte
import js.typedarrays.Uint8Array

fun Uint8Array<*>.toByteArray(): ByteArray = ByteArray(length) { index -> at(index)!!.toByte() }

fun ByteArray.toUint8Array(): Uint8Array<*> = Uint8Array<ArrayBuffer>(size).apply { forEachIndexed { index, byte -> set(index, byte.toJsByte()) } }

But I hope that in the future a more efficient solution could be provided.

[mipastgt]

JSZipObject, e.g., has a function bytes() which returns a Uint8Array. However on the Kotlin side you probably want to use that as a simple ByteArray because that's what other Kotlin APIs expect. At the moment there does not seem to be a conversion function to go directly from a Uint8Array to a ByteArray. There only is one to go to a UByteArray which is a type that is seldom used in Kotlin APIs (because it's new and requires opt in). Of course I could then convert the UByteArray to a ByteArray but that is not only cumbersome, it also requires yet another copy of the whole bytes.

I'd therefore propose two additional conversion functions to go directly from ByteArray -> Uint8Array and vize versa.