@supabase/realtime-js/README.md

Listen to realtime updates to your PostgreSQL database

<br />
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  <h1 align="center">Supabase Realtime Client</h1>

  <h3 align="center">Send ephemeral messages with <b>Broadcast</b>, track and synchronize state with <b>Presence</b>, and listen to database changes with <b>Postgres Change Data Capture (CDC)</b>.</h3>

  <p align="center">
    <a href="https://supabase.com/docs/guides/realtime">Guides</a>
    ·
    <a href="https://supabase.com/docs/reference/javascript">Reference Docs</a>
    ·
    <a href="https://multiplayer.dev">Multiplayer Demo</a>
  </p>
</p>

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[![pkg.pr.new](https://pkg.pr.new/badge/supabase/realtime-js)](https://pkg.pr.new/~/supabase/realtime-js)

</div>

# 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

```bash
npm install @supabase/realtime-js
```

## Creating a Channel

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

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

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`.
- Setting `private` to `true` means that the client will use RLS to determine if the user can connect or not to a given channel.

## Broadcast

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

```js
// 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 acknowledgment that it received the broadcast message request.
- Setting `self` to `true` means that the client will receive the broadcast message it sent out.

### Broadcast Replay

Broadcast Replay enables **private** channels to access messages that were sent earlier. Only messages published via [Broadcast From the Database](https://supabase.com/docs/guides/realtime/broadcast#trigger-broadcast-messages-from-your-database) are available for replay.

You can configure replay with the following options:

- **`since`** (Required): The epoch timestamp in milliseconds, specifying the earliest point from which messages should be retrieved.
- **`limit`** (Optional): The number of messages to return. This must be a positive integer, with a maximum value of 25.

Example:

```typescript
const twelveHours = 12 * 60 * 60 * 1000
const twelveHoursAgo = Date.now() - twelveHours

const config = { private: true, broadcast: { replay: { since: twelveHoursAgo, limit: 10 } } }

supabase
  .channel('main:room', { config })
  .on('broadcast', { event: 'my_event' }, (payload) => {
    if (payload?.meta?.replayed) {
      console.log('This message was sent earlier:', payload)
    } else {
      console.log('This is a new message', payload)
    }
    // ...
  })
  .subscribe()
```

## Presence

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

```js
// Setup...

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

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.

```js
// 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.

```js
// Setup...

client.getChannels()
```

## Cleanup

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

- Remove a single channel

```js
// Setup...

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

channel.unsubscribe()
client.removeChannel(channel)
```

- Remove all channels and close the connection

```js
// Setup...

client.removeAllChannels()
client.disconnect()
```

## Development

This package is part of the [Supabase JavaScript monorepo](https://github.com/supabase/supabase-js). To work on this package:

### Building

```bash
# Complete build (from monorepo root)
npx nx build realtime-js

# Build with watch mode for development
npx nx build realtime-js --watch

# Individual build targets
npx nx build:main realtime-js    # CommonJS build (dist/main/)
npx nx build:module realtime-js  # ES Modules build (dist/module/)

# Other useful commands
npx nx clean realtime-js         # Clean build artifacts
npx nx format realtime-js        # Format code with Prettier
npx nx lint realtime-js          # Run ESLint
npx nx typecheck realtime-js     # TypeScript type checking
```

#### Build Outputs

- **CommonJS (`dist/main/`)** - For Node.js environments
- **ES Modules (`dist/module/`)** - For modern bundlers (Webpack, Vite, Rollup)
- **TypeScript definitions (`dist/module/index.d.ts`)** - Type definitions for TypeScript projects

Note: Unlike some other packages, realtime-js doesn't include a UMD build since it's primarily used in Node.js or bundled applications.

#### Validating Package Exports

```bash
# Check if package exports are correctly configured
npx nx check-exports realtime-js
```

This command uses ["Are the types wrong?"](https://github.com/arethetypeswrong/arethetypeswrong.github.io) to verify that the package exports work correctly in different environments. Run this before publishing to ensure your package can be imported correctly by all consumers.

### Testing

**No Docker or Supabase instance required!** The realtime-js tests use mocked WebSocket connections, so they're completely self-contained.

```bash
# Run unit tests (from monorepo root)
npx nx test realtime-js

# Run tests with coverage report
npx nx test:coverage realtime-js

# Run tests in watch mode during development
npx nx test:watch realtime-js
```

#### Test Scripts Explained

- **test** - Runs all unit tests once using Vitest
- **test:coverage** - Runs tests and generates coverage report with terminal output
- **test:watch** - Runs tests in interactive watch mode for development

The tests mock WebSocket connections using `mock-socket`, so you can run them anytime without any external dependencies.

### Contributing

We welcome contributions! Please see our [Contributing Guide](../../../CONTRIBUTING.md) for details on how to get started.

For major changes or if you're unsure about something, please open an issue first to discuss your proposed changes.

## Credits

This repo draws heavily from [phoenix-js](https://github.com/phoenixframework/phoenix/tree/master/assets/js/phoenix).

## License

MIT.