if (connected) {
        // $FlowFixMe[incompatible-call]
        ws.send(...args);
      }
Returns a WebSocketServer to be attached to an existing HTTP instance. It forwards
the received events on the given "websocketServer" parameter. It must be an
object with the following fields:

  - onClientConnect
  - onClientError
  - onClientMessage
  - onClientDisconnect