How do you implement a webhook system in Node.js?

Question

Accepted Answer

**Webhooks** — HTTP callbacks for event notifications.

```javascript
class WebhookService {
    constructor(db) {
        this.db = db;
    }

async register(event, url, secret) {
        return this.db.webhooks.create({ event, url, secret });
    }

async trigger(event, payload) {
        const hooks = await this.db.webhooks.findByEvent(event);

await Promise.allSettled(
            hooks.map(hook => this.send(hook, payload))
        );
    }

async send(hook, payload) {
        const body = JSON.stringify(payload);
        const signature = crypto
            .createHmac("sha256", hook.secret)
            .update(body)
            .digest("hex");

const response = await fetch(hook.url, {
            method: "POST",
            headers: {
                "Content-Type": "application/json",
                "X-Webhook-Signature": signature,
                "X-Webhook-Event": hook.event,
            },
            body,
        });

if (!response.ok) {
            throw new Error(`Webhook failed: ${response.status}`);
        }
    }
}

// Usage
await webhookService.trigger("order.created", {
    orderId: 123,
    amount: 99.99,
});
```

**Key points:**
- Sign payloads with HMAC.
- Retry failed deliveries.
- Log all attempts.

Node.js: How do you implement a webhook system in Node.js?