How do you implement a pub/sub system with Redis in Node.js?

Question

Accepted Answer

**Pub/Sub** — publish-subscribe messaging pattern.

```javascript
const redis = require("redis");

// Publisher
const publisher = redis.createClient();

async function publish(channel, message) {
    await publisher.publish(channel, JSON.stringify(message));
}

// Subscriber
const subscriber = redis.createClient();

await subscriber.subscribe("notifications", (message) => {
    const data = JSON.parse(message);
    console.log("Received:", data);
});

// Usage
await publish("notifications", {
    type: "order:created",
    orderId: 123,
});
```

**Redis Streams (better for persistence):**
```javascript
// Producer
await redis.xAdd("orders", "*", {
    type: "created",
    orderId: "123",
});

// Consumer (consumer group)
await redis.xGroupCreate("orders", "mygroup", "0");
const messages = await redis.xReadGroup(
    "mygroup", "consumer-1",
    [{ key: "orders", id: ">" }],
    { COUNT: 10, BLOCK: 0 }
);
```

**Key differences:**
- Pub/Sub: fire-and-forget, no persistence.
- Streams: persistent, consumer groups, acknowledgment.

Node.js: How do you implement a pub/sub system with Redis in Node.js?