ServerWebSocket.binaryType

binaryType?: 'arraybuffer' | 'uint8array' | 'nodebuffer'

Sets how binary data is returned in events.

if nodebuffer, binary data is returned as Buffer objects. (default)
if arraybuffer, binary data is returned as ArrayBuffer objects.
if uint8array, binary data is returned as Uint8Array objects.

let ws: WebSocket;
ws.binaryType = "uint8array";
ws.addEventListener("message", ({ data }) => {
  console.log(data instanceof Uint8Array); // true
});