experimental-datpeers-api.js

// control the session data on your connection
experimental.datPeers.getSessionData()
experimental.datPeers.setSessionData(obj) // obj must be no larger than 255 bytes when JSONified

// manage connected peers
var peers = experimental.datPeers.list() // list all peers connected to the current page's dat
var peer  = experimental.datPeers.get(peerId)
await experimental.datPeers.broadcast(data) // send a message to all peers
experimental.datPeers.addEventListener('connect') // new peer
experimental.datPeers.addEventListener('disconnect') // peer closed connection
experimental.datPeers.addEventListener('message') // peer sent a message
experimental.datPeers.addEventListener('session-data') // peer set session data

// DatPeer object
peer.id
peer.sessionData
peer.send(data) // send a message to a peer

// all events:
event.peer // the sending DatPeer object

// message event:
event.data // string, object, or ArrayBuffer

Note about this:

It's scoped to the current page's dat, which is intuitively similar to Single Origin Policy. So, if you're on dat://fritter.hashbase.io, then the peers you'll be seeing/messaging will be your peers for the Fritter site (dat://fritter.hashbase.io).