ws2.js

const connection = new WebSocket(config.pubsub.url);
connection.onopen = () => {
  connection.send({
    subscribe: {
      channel: this.state.user.get('language'),
      user: {
        id: this.state.user.id // Could be named 'username' instead
        data: {} // Attach custom data to a user 
      }
    }
  });
};