Paho Javascript MQTT subscribe to multiple topics

Question

Is it possible to use a similar concept (in javascript) with the message_callback_add used in paho python to use multiple callbacks when the client subscribes to multiple topics? I have seen the use of if conditions in onMessageArrived() but I was wondering whether a more efficient and clean way exists?

var mqtt;                           // MQTT variable/object
var reconnectTimeout = 5000;        // 5 seconds for the reconnectTimeout
var host="localhost";               // MQTT bridge IP
var port=8083;                      // MQTT bridge port 
MQTTconnect();                      // Initialise the MQTT connections

function MQTTconnect(){
  console.log("mqtt connecting to " + host + ":" + port);
  mqtt = new Paho.MQTT.Client(host, port, "client_test");
  var options = {
    timeout: 100,
    onSuccess: onConnect,
    onFailure: onFailure,
  };
  mqtt.onMessageArrived = onMessageArrived;
  mqtt.connect(options); // connect
}

function onConnect(){
  console.log("Mqtt Connected - Subscribe to the topics");
  mqtt.subscribe("topic1/a");
  mqtt.subscribe("topic2/b");
}
            
function onFailure(message){
  console.log("Connection attempt to MQTT " + host + " failed");
  setTimeout(MQTTconnect, reconnectTimeout);
}

function onMessageArrived(msg){
  if (msg.destinationName == "topic1/a"){
    console.log("Topic1: ", msg.payloadString);
  }
  else if (msg.destinationName == "topic2/b"){
    console.log("Topic2: ", msg.payloadString);
  }
}

It seems there is no way to achieve it there. I'm using a switch case currently. — Mr.

hardillb hardillb · Accepted Answer · 2021-06-07T12:16:03

No, there is only one callback from all messages in the JavaScript.

The only option is to check the topic and branch as needed in the onMessageArrived callback

Paho Javascript MQTT subscribe to multiple topics

1 Answers