Presence

A presence channel lists who is on it to everyone on it, and says when someone arrives and leaves.

Node

realtime.channel( 'presence-room-', async ( user, channel ) => {
    if ( user === null || !( await mayEnter( user, channel ) ) ) return false;
    return { info: { name: await nameOf( user ), role: 'agent' } };   // what the others see; your profile's name by default
} );

PHP

$realtime->channel( 'presence-room-', function ( $user, $channel ) {
    if ( null === $user || ! may_enter( $user, $channel ) ) {
        return false;
    }
    return [ 'info' => [ 'name' => name_of( $user ), 'role' => 'agent' ] ];   // what the others see; your profile's name by default
} );

// Laravel: routes/channels.php, where an array is the member's info. PresenceChannel( 'room.7' ) is presence-room.7 here.
Broadcast::channel( 'room.{id}', fn ( User $user, string $id ) => $user->canEnter( $id ) ? [ 'name' => $user->name, 'role' => 'agent' ] : false );

Python

def may_enter_room(user, channel):
    if user is None or not may_enter(user, channel):
        return False
    return {"info": {"name": name_of(user), "role": "agent"}}   # what the others see; your profile's name by default

realtime.channel("presence-room-", may_enter_room)

• A member is the asking user (id, their id as a string), unless the answer names another id: a visitor you know by a session id, for example.
• Nobody, without an id in the answer, is refused.
• info is at most 1 KB, sealed with the channel's key: WordPlus Cloud lists members without reading it.

const room = rt.subscribe( 'presence-room-7' );
room.on( 'realtime:subscribed', () => draw( room.members() ) );          // [ { id, info } ]
room.on( 'realtime:member_added', ( member ) => add( member ) );          // { id, info }
room.on( 'realtime:member_removed', ( member ) => remove( member.id ) );

• A user with several tabs or devices is one member: they leave when their last connection does.
• A move to another server shows nobody leaving.
• 1,000 members a channel, the first 100 listed when subscribing; room.memberCount is the whole count.

In React, usePresence( 'presence-room-7' ) gives the members and updates with them (React).