Guacamole lite Send error code and messages

Question

I am currently using nodejs and gaucamole lite but i would like to send an error back to the client / browser where I initiate the connection from guacamole-common-js?

const GuacdClient = require('./GuacdClient.js');
class ClientConnection {

    processReceivedMessage(message) {
            this.lastActivity = Date.now();
            this.guacdClient.send(message);
        }
 }

I am lost as to where send an error code back to the common-js.js library in the browser. Is this the client on the nodeJs? I really would like to manage error codes over the websocket or even code or messages on connecting to make it a bit more granualar.

Any advice?