Topic with more than one, same or different, callbacks

[GHNewbiee]

Hi,

As per doc :

const pubsub = new PubSub();

pubsub.subscribe('message', listener);
pubsub.subscribe('message', listener);
pubsub.subscribe('another_message', listener);

• What is the purpose of subscribing the same callback (listener) more than one to a topic?

Considering that the second callback is different (eg listener2), like

const pubsub = new PubSub();

pubsub.subscribe('message', listener1);
pubsub.subscribe('message', listener2);

or as per doc

const pubsub = new PubSub();

pubsub.subscribe('message', listener1);
pubsub.subscribeOnce('message', listener2);
pubsub.subscribe('another_message', listener1);

• How do you decide which callback (listener1 or listener2) is called when publish or publishSync accepts as argument only the topic and not the token by means of which a specific callback could be used, eg

const pubsub = new PubSub();

const token1 = pubsub.subscribe('message', listener1)
const token2 = pubsub.subscribe('message', listener2)
const token3 = pubsub.subscribeOnce('message', listener3);

pubsub.publish(token1, data1);
pubsub.publish(token2, data2);
pubsub.publish(token3, data3);

Tia