---
title: Use SWR for Automatic Deduplication
impact: MEDIUM-HIGH
impactDescription: automatic deduplication
tags: client, swr, deduplication, data-fetching
---

## Use SWR for Automatic Deduplication

SWR enables request deduplication, caching, and revalidation across component instances.

**Incorrect (no deduplication, each instance fetches):**

```tsx
function UserList() {
  const [users, setUsers] = useState([]);
  useEffect(() => {
    fetch("/api/users")
      .then((r) => r.json())
      .then(setUsers);
  }, []);
}
```

**Correct (multiple instances share one request):**

```tsx
import useSWR from "swr";

function UserList() {
  const { data: users } = useSWR("/api/users", fetcher);
}
```

**For immutable data:**

```tsx
import { useImmutableSWR } from "@/lib/swr";

function StaticContent() {
  const { data } = useImmutableSWR("/api/config", fetcher);
}
```

**For mutations:**

```tsx
import { useSWRMutation } from "swr/mutation";

function UpdateButton() {
  const { trigger } = useSWRMutation("/api/user", updateUser);
  return <button onClick={() => trigger()}>Update</button>;
}
```

Reference: [https://swr.vercel.app](https://swr.vercel.app)