Overview

This client enables you to use the following Supabase Realtime's features:

• Broadcast: send ephemeral messages from client to clients with minimal latency. Use cases include sharing cursor positions between users.
• Presence: track and synchronize shared state across clients with the help of CRDTs. Use cases include tracking which users are currently viewing a specific webpage.
• Postgres Change Data Capture (CDC): listen for changes in your PostgreSQL database and send them to clients.

Usage

Installing the Package

npm install @supabase/realtime-js

Creating a Channel

import { RealtimeClient } from '@supabase/realtime-js'

const client = new RealtimeClient(REALTIME_URL, {
  params: {
    apikey: API_KEY,
    eventsPerSecond: 10,
  },
})

const channel = client.channel('test-channel', {})

channel.subscribe((status, err) => {
  if (status === 'SUBSCRIBED') {
    console.log('Connected!')
  }

  if (status === 'CHANNEL_ERROR') {
    console.log(`There was an error subscribing to channel: ${err.message}`)
  }

  if (status === 'TIMED_OUT') {
    console.log('Realtime server did not respond in time.')
  }

  if (status === 'CLOSED') {
    console.log('Realtime channel was unexpectedly closed.')
  }
})

Notes:

• REALTIME_URL is 'ws://localhost:4000/socket' when developing locally and 'wss://<project_ref>.supabase.co/realtime/v1' when connecting to your Supabase project.
• API_KEY is a JWT whose claims must contain exp and role (existing database role).
• Channel name can be any string.
• eventsPerSecond, or client-side rate limiting, enforces the number of events sent to the Realtime server uniformly spread across a second. The default is 10, which means that the client can send one event, whether that's Broadcast/Presence/Postgres CDC, every 100 milliseconds. You may change this as you see fit but note that the server's rate limiting will need to be updated accordingly. You can learn more about Realtime's rate limits here: https://supabase.com/docs/guides/realtime/rate-limits.

Broadcast

Your client can send and receive messages based on the event.

// Setup...

const channel = client.channel('broadcast-test', { broadcast: { ack: false, self: false } })

channel.on('broadcast', { event: 'some-event' }, (payload) =>
  console.log(payload)
)

channel.subscribe(async (status) => {
  if (status === 'SUBSCRIBED') {
    // Send message to other clients listening to 'broadcast-test' channel
    await channel.send({
      type: 'broadcast',
      event: 'some-event',
      payload: { hello: 'world' },
    })
  }
})

Notes:

• Setting ack to true means that the channel.send promise will resolve once server replies with acknowledgement that it received the broadcast message request.
• Setting self to true means that the client will receive the broadcast message it sent out.

Presence

Your client can track and sync state that's stored in the channel.

// Setup...

const channel = client.channel('presence-test', { presence: { key: '' } })

channel.on('presence', { event: 'sync' }, () => {
  console.log('Online users: ', channel.presenceState())
})

channel.on('presence', { event: 'join' }, ({ newPresences }) => {
  console.log('New users have joined: ', newPresences)
})

channel.on('presence', { event: 'leave' }, ({ leftPresences }) => {
  console.log('Users have left: ', newPresences)
})

channel.subscribe(async (status) => {
  if (status === 'SUBSCRIBED') {
    const status = await channel.track({ 'user_id': 1 })
    console.log(status)
  }
})

Postgres CDC

Receive database changes on the client.

// Setup...

const channel = client.channel('db-changes')

channel.on('postgres_changes', { event: '*', schema: 'public' }, (payload) => {
  console.log('All changes in public schema: ', payload)
})

channel.on('postgres_changes', { event: 'INSERT', schema: 'public', table: 'messages' }, (payload) => {
  console.log('All inserts in messages table: ', payload)
})

channel.on('postgres_changes', { event: 'UPDATE', schema: 'public', table: 'users', filter: 'username=eq.Realtime' }, (payload) => {
  console.log('All updates on users table when username is Realtime: ', payload)
})

channel.subscribe(async (status) => {
  if (status === 'SUBSCRIBED') {
    console.log('Ready to receive database changes!')
  }
})

Get All Channels

You can see all the channels that your client has instantiatied.

// Setup...

client.getChannels()

Cleanup

It is highly recommended that you clean up your channels after you're done with them.

• Remove a single channel

// Setup...

const channel = client.channel('some-channel-to-remove')

channel.subscribe()

client.removeChannel(channel)

• Remove all channels

// Setup...

const channel1 = client.channel('a-channel-to-remove')
const channel2 = client.channel('another-channel-to-remove')

channel1.subscribe()
channel2.subscribe()

client.removeAllChannels()

Credits

This repo draws heavily from phoenix-js.

License

MIT.