const PeerMonitor = require('ipfs-pubsub-peer-monitor')

// Get an IPFS instance somehow
const ipfs = ...

// Topic to monitor
const topic = 'abc'

// Make sure to subscribe to the channel before monitoring it!
ipfs.pubsub.subscribe(topic, (message) => {}, (err, res) => {})

// Pass an IPFS pubsub object and the topic to the monitor
const topicMonitor = new PeerMonitor(ipfs.pubsub, topic)

// When a peer joins the topic
topicMonitor.on('join', peer => console.log("Peer joined", peer))
topicMonitor.on('leave', peer => console.log("Peer left", peer))
topicMonitor.on('error', e => console.error(e))