ably-realtime（巧妙地实时）

Ably Realtime for React/TypeScript

Ably Realtime is a platform for building scalable real-time applications with pub-sub messaging, presence tracking, collaborative features, chat, and database synchronization.

When to Use Each Feature

Ably provides different abstractions for different real-time use cases:

• Channels (Core Pub-Sub): Custom real-time messaging, notifications, live updates, event broadcasting
• Spaces: Participant state in collaborative UIs (live cursors, avatar stacks, user locations, component locking)
• LiveObjects: Application state synchronization (counters, voting, shared configurations, game state) with conflict-free updates
• Chat SDK: Complete messaging apps (1:1 chat, group conversations, livestream chat, support tickets)
• LiveSync: Database-to-client synchronization (broadcasting Postgres changes, outbox pattern, transactional consistency)

Installation

# Core Ably (required)
npm install ably

# Additional packages (install as needed)
npm install @ably/spaces           # For Spaces
npm install @ably/chat             # For Chat SDK
npm install @ably-labs/models      # For LiveSync Models SDK

Basic Setup

All Ably features require a Realtime client. Create the client outside React components to prevent reconnections on re-renders:

// main.tsx or app.tsx
import * as Ably from 'ably';
import { AblyProvider } from 'ably/react';

// Create client OUTSIDE components
const realtimeClient = new Ably.Realtime({
  key: import.meta.env.VITE_ABLY_API_KEY,
  clientId: 'unique-user-id', // Required for Spaces and Chat
});

function Root() {
  return (
    <AblyProvider client={realtimeClient}>
      <App />
    </AblyProvider>
  );
}

For production applications, use token authentication instead of API keys. See references/auth-security.md.

Quick Start: Channels (Core Pub-Sub)

Basic real-time messaging with channels:

import { ChannelProvider, useChannel } from 'ably/react';

// Wrap with ChannelProvider
<ChannelProvider channelName="notifications">
  <NotificationComponent />
</ChannelProvider>

// Use in component
function NotificationComponent() {
  const { publish } = useChannel('notifications', (message) => {
    console.log('Received:', message.data);
    // Update local state with message
  });

  const sendNotification = () => {
    publish('alert', { text: 'New update!', timestamp: Date.now() });
  };

  return <button onClick={sendNotification}>Send</button>;
}

For detailed channel operations, presence tracking, and history, see references/channels/.

Quick Start: Spaces (Collaborative UI)

Track participant state for collaborative features:

import Spaces from '@ably/spaces';
import { SpacesProvider, SpaceProvider, useMembers, useCursors } from '@ably/spaces/react';

// Setup (in root)
const spaces = new Spaces(realtimeClient);

<SpacesProvider client={spaces}>
  <SpaceProvider name="my-collaborative-space">
    <CollaborativeEditor />
  </SpaceProvider>
</SpacesProvider>

// Avatar stack
function AvatarStack() {
  const { self, others } = useMembers();

  return (
    <div>
      <Avatar user={self} />
      {others.map(member => (
        <Avatar key={member.connectionId} user={member} />
      ))}
    </div>
  );
}

// Live cursors
function CursorTracking() {
  const { set } = useCursors((update) => {
    // Render other users' cursors
    renderCursor(update.connectionId, update.position);
  });

  useEffect(() => {
    const handleMove = (e: MouseEvent) => {
      set({ position: { x: e.clientX, y: e.clientY } });
    };
    window.addEventListener('mousemove', handleMove);
    return () => window.removeEventListener('mousemove', handleMove);
  }, [set]);

  return <canvas id="cursor-layer" />;
}

For locations, component locking, and advanced patterns, see references/spaces/.

Quick Start: LiveObjects (Shared State)

⚠️ Public Preview: LiveObjects API may change before general availability.

Conflict-free shared state synchronization:

import { LiveCounter, LiveMap } from "ably/liveobjects";

async function setupSharedState() {
  const channel = realtimeClient.channels.get("game:lobby-1");
  const gameState = await channel.object.get();

  // Create shared counter
  await gameState.set("score", LiveCounter.create(0));

  // Create shared map
  await gameState.set(
    "players",
    LiveMap.create({
      player1: { name: "Alice", ready: false },
      player2: { name: "Bob", ready: false },
    }),
  );

  // Subscribe to changes
  gameState.get("score").subscribe(() => {
    console.log("Score:", gameState.get("score").value());
  });

  // Update values
  await gameState.get("score").increment(10);
  await gameState.get("players").set("player1", { name: "Alice", ready: true });
}

React integration:

function GameLobby() {
  const [score, setScore] = useState(0);
  const [players, setPlayers] = useState({});

  useEffect(() => {
    let gameState: any;

    async function init() {
      const channel = realtimeClient.channels.get('game:lobby-1');
      gameState = await channel.object.get();

      // Subscribe to updates
      gameState.get('score').subscribe(() => {
        setScore(gameState.get('score').value());
      });

      gameState.get('players').subscribe(() => {
        setPlayers(gameState.get('players').value());
      });
    }

    init();

    return () => {
      // Cleanup subscriptions
    };
  }, []);

  return (
    <div>
      <h2>Score: {score}</h2>
      {Object.entries(players).map(([id, player]: [string, any]) => (
        <div key={id}>{player.name} - {player.ready ? '✓' : '...'}</div>
      ))}
    </div>
  );
}

For LiveMap batch operations, composability, and detailed API, see references/liveobjects/.

Quick Start: Chat SDK

Purpose-built chat with rooms, messages, typing indicators, and reactions:

import { ChatClient } from '@ably/chat';
import { ChatClientProvider, ChatRoomProvider, useMessages, useTyping } from '@ably/chat/react';

// Setup (in root)
const chatClient = new ChatClient(realtimeClient);

<ChatClientProvider client={chatClient}>
  <ChatRoomProvider name="support:ticket-123">
    <ChatRoom />
  </ChatRoomProvider>
</ChatClientProvider>

// Chat component
function ChatRoom() {
  const [messages, setMessages] = useState<Message[]>([]);
  const { currentlyTyping, keystroke } = useTyping();

  const { send, getPreviousMessages } = useMessages({
    listener: (event) => {
      if (event.type === 'created') {
        setMessages(prev => [...prev, event.message]);
      }
    }
  });

  useEffect(() => {
    // Load history
    getPreviousMessages({ limit: 50 }).then(result => {
      setMessages(result.items.reverse());
    });
  }, []);

  const handleSend = (text: string) => {
    send({ text });
  };

  const handleTyping = () => {
    keystroke(); // Triggers typing indicator
  };

  return (
    <div>
      <MessageList messages={messages} />
      {currentlyTyping.length > 0 && (
        <TypingIndicator users={currentlyTyping} />
      )}
      <MessageInput onSend={handleSend} onKeyPress={handleTyping} />
    </div>
  );
}

For message updates/deletes, reactions, presence, and room lifecycle, see references/chat/.

Quick Start: LiveSync (Database Sync)

Broadcast database changes from PostgreSQL/Neon to clients:

Backend (Database + Outbox):

-- Outbox table for change events
CREATE TABLE outbox (
  sequence_id serial PRIMARY KEY,
  mutation_id TEXT NOT NULL,
  channel TEXT NOT NULL,
  name TEXT NOT NULL,
  data JSONB,
  processed BOOLEAN DEFAULT false
);

-- Trigger to notify on changes
CREATE FUNCTION outbox_notify() RETURNS trigger AS $$
BEGIN
  PERFORM pg_notify('ably_adbc', '');
  RETURN NULL;
END;
$$ LANGUAGE plpgsql;

CREATE TRIGGER outbox_trigger
  AFTER INSERT ON outbox
  FOR EACH STATEMENT
  EXECUTE PROCEDURE outbox_notify();

// API route - transactional write
export async function POST(req: Request) {
  const { documentId, content } = await req.json();

  await db.transaction(async (trx) => {
    // Update application data
    await trx("documents")
      .where({ id: documentId })
      .update({ content, updated_at: new Date() });

    // Insert change event
    await trx("outbox").insert({
      mutation_id: crypto.randomUUID(),
      channel: `document:${documentId}`,
      name: "document.updated",
      data: { id: documentId, content },
    });
  });

  return Response.json({ success: true });
}

Frontend (Subscribe to Changes):

function DocumentEditor({ documentId }: { documentId: string }) {
  const [content, setContent] = useState('');

  const { channel } = useChannel(`document:${documentId}`, (message) => {
    if (message.name === 'document.updated') {
      setContent(message.data.content);
    }
  });

  useEffect(() => {
    // Load initial state
    fetch(`/api/documents/${documentId}`)
      .then(r => r.json())
      .then(doc => setContent(doc.content));
  }, [documentId]);

  return <textarea value={content} onChange={(e) => setContent(e.target.value)} />;
}

For Models SDK with optimistic updates, integration setup, and advanced patterns, see references/livesync/.

Common Patterns

Pattern: Load History Before Subscribing

function ChatWithHistory() {
  const [messages, setMessages] = useState<any[]>([]);

  const { channel } = useChannel('chat', (message) => {
    setMessages(prev => [...prev, message]);
  });

  useEffect(() => {
    async function loadHistory() {
      const history = await channel.history({ limit: 50 });
      setMessages(history.items.reverse());
    }
    loadHistory();
  }, [channel]);

  return <MessageList messages={messages} />;
}

Pattern: Optimistic Updates with Confirmation

function OptimisticComment({ postId }: { postId: string }) {
  const [comments, setComments] = useState<Comment[]>([]);
  const pendingMutations = useRef(new Map());

  useChannel(`post:${postId}`, (message) => {
    const mutationId = message.data.mutation_id;

    // Remove optimistic entry, add confirmed
    if (pendingMutations.current.has(mutationId)) {
      setComments(prev => {
        const withoutOptimistic = prev.filter(c => c.id !== mutationId);
        return [...withoutOptimistic, message.data];
      });
      pendingMutations.current.delete(mutationId);
    } else {
      setComments(prev => [...prev, message.data]);
    }
  });

  const addComment = async (text: string) => {
    const mutationId = crypto.randomUUID();
    const optimistic = { id: mutationId, text, pending: true };

    // Add optimistically
    setComments(prev => [...prev, optimistic]);
    pendingMutations.current.set(mutationId, optimistic);

    // Send to backend
    await fetch('/api/comments', {
      method: 'POST',
      body: JSON.stringify({ mutationId, postId, text })
    });
  };

  return <CommentList comments={comments} onAdd={addComment} />;
}

Pattern: Presence with Profile Data

import { usePresence, usePresenceListener } from 'ably/react';

function OnlineUsers() {
  usePresence('room', {
    username: 'Alice',
    avatar: '/avatars/alice.jpg',
    status: 'active'
  });

  const { presenceData } = usePresenceListener('room');

  return (
    <div>
      <h3>Online ({presenceData.length})</h3>
      {presenceData.map(member => (
        <div key={member.connectionId}>
          <img src={member.data?.avatar} alt={member.data?.username} />
          <span>{member.data?.username}</span>
          <span>{member.data?.status}</span>
        </div>
      ))}
    </div>
  );
}

Pattern: Connection State Monitoring

import { useConnectionStateListener, useAbly } from 'ably/react';

function ConnectionStatus() {
  const ably = useAbly();
  const [state, setState] = useState(ably.connection.state);
  const [error, setError] = useState<string | null>(null);

  useConnectionStateListener((stateChange) => {
    setState(stateChange.current);

    if (stateChange.current === 'failed' || stateChange.current === 'suspended') {
      setError(stateChange.reason?.message || 'Connection issue');
    } else {
      setError(null);
    }
  });

  return (
    <div className={`status-${state}`}>
      {state === 'connected' ? '🟢' : '🔴'} {state}
      {error && <span>{error}</span>}
    </div>
  );
}

TypeScript Types

Ably provides comprehensive TypeScript definitions. Import types as needed:

import type * as Ably from "ably";
import type { Message } from "@ably/chat";
import type { SpaceMember, CursorUpdate } from "@ably/spaces";

const handleMessage = (msg: Ably.Message) => {
  console.log(msg.name, msg.data, msg.timestamp);
};

const handleCursor = (update: CursorUpdate) => {
  const position: { x: number; y: number } = update.position;
};

Progressive References

For detailed documentation on specific features:

• Core Channels - Channel operations, presence, history, connection management
• Spaces - Setup, React hooks (useMembers, useCursors, useLocations, useLocks), patterns
• LiveObjects - Overview, API reference (LiveCounter, LiveMap), composability, batch operations
• Chat SDK - Setup, React hooks (useMessages, useTyping, useRoomReactions), message CRUD, features
• LiveSync - Outbox pattern, integration setup, Models SDK, optimistic updates, React patterns
• Auth & Security - Token authentication, clientId, capabilities, production best practices

Troubleshooting

Connection limit exceeded

Each Realtime client instance creates a connection. Create the client once outside React components:

// ❌ Wrong - creates new connection on every render
function App() {
  const client = new Ably.Realtime({ key });
  return <AblyProvider client={client}>...</AblyProvider>;
}

// ✅ Correct - single connection
const client = new Ably.Realtime({ key });
function App() {
  return <AblyProvider client={client}>...</AblyProvider>;
}

Provider nesting issues

Ensure correct provider hierarchy:

// For Spaces
<AblyProvider client={realtimeClient}>
  <SpacesProvider client={spacesClient}>
    <SpaceProvider name="space-name">
      {/* Your components */}
    </SpaceProvider>
  </SpacesProvider>
</AblyProvider>

// For Chat
<AblyProvider client={realtimeClient}>
  <ChatClientProvider client={chatClient}>
    <ChatRoomProvider name="room-name">
      {/* Your components */}
    </ChatRoomProvider>
  </ChatClientProvider>
</AblyProvider>

Channel not receiving messages

1. Check channel name matches exactly (case-sensitive)
2. Verify API key has required capabilities
3. Ensure clientId is set when using presence or Chat
4. Check connection state with useConnectionStateListener

LiveObjects not syncing

1. Verify LiveObjects is enabled in your Ably app (Dashboard → Settings)
2. Check channel is attached: channel.state === 'attached'
3. Ensure proper await on async operations
4. LiveObjects requires Ably protocol version 2 (set automatically)

Chat messages not persisting

Chat messages persist for 30 days by default. Check:

1. Ably app has Chat enabled
2. Room is properly attached before sending
3. Message has required fields (text or metadata)
4. API key has publish capability

Best Practices

1. Single Realtime Client: Create one client instance per application, share across components
2. ClientId for Identity: Always set clientId when using Spaces or Chat for user identification
3. Channel Naming: Use hierarchical names for organization: post:123, room:lobby:1, user:alice:notifications
4. Presence Data: Keep presence data small (under 1KB) for efficiency
5. History Limits: Load only necessary history to reduce bandwidth and latency
6. Error Handling: Monitor connection state and handle disconnections gracefully
7. Token Auth in Production: Never expose API keys in client code, use token authentication
8. Cleanup: Unsubscribe from channels and detach when components unmount (hooks handle this automatically)
9. LiveObjects Conflicts: Design for eventual consistency, use LiveCounter for numeric aggregations
10. LiveSync Transactions: Always write to outbox within same transaction as application data

Additional Resources

• Ably Documentation
• React Hooks Documentation
• Spaces Documentation
• Chat SDK Documentation
• LiveObjects Documentation
• LiveSync Documentation