WebSocket: binaryType property - Web APIs | MDN

js
// Create WebSocket connection.
const socket = new WebSocket("ws://localhost:8080");

// Change binary type from "blob" to "arraybuffer"
socket.binaryType = "arraybuffer";

// Listen for messages
socket.addEventListener("message", (event) => {
if (event.data instanceof ArrayBuffer) {
// binary frame
const view = new DataView(event.data);
console.log(view.getInt32(0));
} else {
// text frame
console.log(event.data);
});