Presence
Share state between users with Realtime Presence.
Let's explore how to implement Realtime Presence to track state between multiple users.
Usage#
You can use the Supabase client libraries to track Presence state between users.
Initialize the client#
Go to your Supabase project's API Settings and grab the URL and anon public API key.
_10import { createClient } from '@supabase/supabase-js'_10_10const SUPABASE_URL = 'https://<project>.supabase.co'_10const SUPABASE_KEY = '<your-anon-key>'_10_10const supabase = createClient(SUPABASE_URL, SUPABASE_KEY)
Sync and track state#
Listen to the sync, join, and leave events triggered whenever any client joins or leaves the channel or changes their slice of state:
_14const roomOne = supabase.channel('room_01')_14_14roomOne_14 .on('presence', { event: 'sync' }, () => {_14 const newState = roomOne.presenceState()_14 console.log('sync', newState)_14 })_14 .on('presence', { event: 'join' }, ({ key, newPresences }) => {_14 console.log('join', key, newPresences)_14 })_14 .on('presence', { event: 'leave' }, ({ key, leftPresences }) => {_14 console.log('leave', key, leftPresences)_14 })_14 .subscribe()
Sending state#
You can send state to all subscribers using track():
_13const roomOne = supabase.channel('room_01')_13_13const userStatus = {_13 user: 'user-1',_13 online_at: new Date().toISOString(),_13}_13_13roomOne.subscribe(async (status) => {_13 if (status !== 'SUBSCRIBED') { return }_13_13 const presenceTrackStatus = await roomOne.track(userStatus)_13 console.log(presenceTrackStatus)_13})
A client will receive state from any other client that is subscribed to the same topic (in this case room_01). It will also automatically trigger its own sync and join event handlers.
Stop tracking#
You can stop tracking presence using the untrack() method. This will trigger the sync and leave event handlers.
_10const untrackPresence = async () => {_10 const presenceUntrackStatus = await roomOne.untrack()_10 console.log(presenceUntrackStatus)_10}_10_10untrackPresence()
Presence options#
You can pass configuration options while initializing the Supabase Client.
Presence Key#
By default, Presence will generate a unique UUIDv1 key on the server to track a client channel's state. If you prefer, you can provide a custom key when creating the channel. This key should be unique among clients.
_10import { createClient } from '@supabase/supabase-js'_10_10const channelC = supabase.channel('test', {_10 config: {_10 presence: {_10 key: 'userId-123',_10 },_10 },_10})