swr

Call useSWR with a unique key (usually the API URL) and a fetcher function that returns a promise. The hook returns data, error, isLoading, isValidating, and mutate, and automatically caches and deduplicates requests sharing the same key.

Use useSWRMutation from swr/mutation with a trigger function to perform remote updates. Pass optimisticData, rollbackOnError, populateCache, and revalidate options to update the UI instantly and roll back if the request fails.

Yes, useSWRInfinite from swr/infinite handles paginated and infinite-scroll data. Provide a getKey function that returns the URL per page index (or null to stop), then call setSize to load additional pages.

Pass null or a falsy value as the key to skip fetching, such as useSWR(userId ? `/api/user/${userId}` : null, fetcher). Never call the hook conditionally; use conditional keys instead to comply with React hook rules.

SWR retries on error by default using exponential backoff. Customize behavior with the onErrorRetry option to skip retries for specific status codes like 404 or to cap the maximum retry count.

Yes, useSWRSubscription from swr/subscription connects to real-time sources like WebSockets or SSE. The subscribe function receives a next(error, data) callback and must return a cleanup function; multiple components with the same key share one subscription.