How to use the sharedb function in sharedb

const server = http.createServer(app);
  let db = null;
  if (CollabServer.options.db.type === 'mongo') {
    db = CollabServer.options.db.url
      ? ShareDBMongo(CollabServer.options.db.url)
      : {};
    console.log('CollabServer: Using MongoDB adapter');
  } else {
    console.log(
      'CollabServer: No Database specified, falling back to In Memory'
    );
  }

  // Create the ShareDB backend (that will need to be exported)
  ShareDB.types.register(RichText.type);
  CollabServer.backend = new ShareDB({ db });

  // Create the Websocket server
  new WebSocket.Server({ server }).on('connection', function(ws) {
    CollabServer.backend.listen(new WebsocketJSONStream(ws));
    console.log('New socket client on CollabServer instance');
  });

  server.listen(CollabServer.options.port, function(err) {
    if (err) throw err;
    console.log(
      'CollabServer: Server listening on port ' + CollabServer.options.port
    );
  });
};