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kotlinlang

Is there a way to convert ArrayBuffer to a ByteArray?

You can create Int8Array around the buffer and then unsafe cast it to ByteArray

You can find other type mappings here: <https://kotlinlang.org/docs/reference/js-to-kotlin-interop.html#representing-kotlin-types-in-javascript>

Thank you so much !!!!! It worked ! For days I am trying to get a file to upload correctly to a backend through ktor-client !

```
@Suppress("CAST_NEVER_SUCCEEDS")
fun ArrayBuffer?.asByteArray(): ByteArray? = this?.run { Int8Array(this) as ByteArray }
```

Great! We highly appreciate feedback. Please let us know if you have any inconveniences.

I’d like that function to be part of kotlin/js by default

Since we know for sure that `ByteArray` and `Int8Array` are the same things on runtime we can use:
```
fun ArrayBuffer?.asByteArray(): ByteArray? =
   this?.run { Int8Array(this).unsafeCast&lt;ByteArray&gt;() }
```
This will eliminate unnecesary type check and we don't have to use `@Suppress`

Generated code for `unsafeCast` would be:
```
return $receiver != null ? new Int8Array($receiver) : null;
```
compared to `as` version:
```
    var tmp$;
    if ($receiver != null) {
      var tmp$_0;
      tmp$ = Kotlin.isByteArray(tmp$_0 = new Int8Array($receiver)) ? tmp$_0 : throwCCE();
    }
     else
      tmp$ = null;
    return tmp$;
```

&gt; I’d like that function to be part of kotlin/js by default
Could you file a feature request at <http://kotl.in/issue|kotl.in/issue>?

I didn’t know about unsafeCast, I am going to apply it everywhere needed now

`unsafeCast` has downsides, if cast fails your program will fail the JavaScript way: usually farther down the execution with ambiguous error message :grin:

<https://youtrack.jetbrains.com/issue/KT-30098?project=kt>