Create typed arrays from Go

[Sina M]

Hello! I was wondering if it's possible to create a Uint8Array in Go and pass it to the JS code. I see there are functions like Runtime.newUint8Array but they are not exposed publicly. The workaround I came up for now is a JS function which takes in an array and returns a buffer and invoke that in Go, and pass the returned value again to JS which has unnecessary overhead.

[Dmitry Panov]

Hi. You can do rt.New(rt.Get("Uint8Array")) (possibly cache rt.Get("Uint8Array") if you plan to do it many times and you don't override Uint8Array in your runtime).

[Sina M]

Ok I managed to get it working with your suggestion, thanks. Closing this issue but please consider exposing those methods publicly.

[Sina M]

Hey, just posting this for people who need to do the same thing:

func toBuf(vm *goja.Runtime, bufType goja.Value, val []byte) (goja.Value, error) {
      // bufType is cached `vm.Get("Uint8Array")`
     return vm.New(bufType, vm.ToValue(vm.NewArrayBuffer(val)))
}

Note by first casting to ArrayBuffer you'll avoid copying and get a significant speed-up.

And to get a buffer from JS:

func fromBuf(vm *goja.Runtime, bufType goja.Value, buf goja.Value) ([]byte, error) {
    obj := buf.ToObject(vm)
    if !obj.Get("constructor").SameAs(bufType) {
        return nil, errors.New("invalid buffer")
    }
    b := obj.Get("buffer").Export().(goja.ArrayBuffer).Bytes()
    return b, nil
}