After a connection has been successfully established with the MQTT server, the specified callback in the this.mqttConnectOptions.onSuccess attribute will be executed, that is, the onConnectSuccess function. This function receives an invocationContext object as an argument. The code can access the object we assigned to this.mqttConnectOptions.invocationContext in invocationContext.invocationContext. Thus, the code can retrieve the instance of Paho.MQTT.Client, which established the connection with the MQTT server in the invocationContext.invocationContext.client attribute.
First, the onSuccess function updates the status text to indicate that the client is connected with the MQTT server. Then, the code saves Paho.MQTT.Client, which established the connection in the client variable. Finally, a for loop calls the client.subscribe method three times to subscribe to the following topics: home/results/leds/1, home/results/leds/2, and home/results/leds/3.