ws.js

parseFrame(buffer) {
  // ... first and second byte processing ...

  const isMasked = Boolean((secondByte >>> 7) & 0b00000001); // get first bit of a second byte

  if (isMasked) {
    const maskingKey = buffer.readUInt32BE(offset); // read 4-byte (32-bit) masking key
    offset += 4;
    const payload = buffer.subarray(offset);
    const result = this._unmask(payload, maskingKey);
    return result.toString('utf-8');
  }

  return buffer.subarray(offset).toString('utf-8');
}