How do you implement server-side caching in Node.js?

Question

Accepted Answer

**Server-side caching** — stores frequently accessed data in fast storage.

**Using NodeCache (in-memory):**
```javascript
const NodeCache = require("node-cache");
const cache = new NodeCache({ stdTTL: 300 }); // 5 min

app.get("/users/:id", async (req, res) => {
    const key = `user_${req.params.id}`;
    let user = cache.get(key);

if (!user) {
        user = await db.getUser(req.params.id);
        cache.set(key, user);
    }

res.json(user);
});
```

**Using Redis (distributed):**
```javascript
const redis = require("redis").createClient();

async function getCached(key, fetchFn, ttl = 300) {
    let data = await redis.get(key);
    if (data) return JSON.parse(data);

data = await fetchFn();
    await redis.setEx(key, ttl, JSON.stringify(data));
    return data;
}

// Usage
app.get("/products", async (req, res) => {
    const products = await getCached("products", () => db.getProducts());
    res.json(products);
});
```

**Cache strategies:**
- **Cache-aside** — app checks cache first.
- **Write-through** — update cache on write.
- **TTL** — expire after time.

Node.js: How do you implement server-side caching in Node.js?