SWR is a React Hooks library for data fetching.
The name “SWR” is derived from stale-while-revalidate
, a cache invalidation strategy popularized by HTTP RFC 5861.
SWR first returns the data from cache (stale), then sends the request (revalidate), and finally comes with the up-to-date data again.
With just one hook, you can significantly simplify the data fetching logic in your project. And it also covered in all aspects of speed, correctness, and stability to help you build better experiences:
- Fast, lightweight and reusable data fetching
- Transport and protocol agnostic
- Built-in cache and request deduplication
- Real-time experience
- Revalidation on focus
- Revalidation on network recovery
- Polling
- Pagination and scroll position recovery
- SSR and SSG
- Local mutation (Optimistic UI)
- Built-in smart error retry
- TypeScript
- React Suspense
- React Native
...and a lot more.
With SWR, components will get a stream of data updates constantly and automatically. Thus, the UI will be always fast and reactive.
View full documentation and examples on swr.vercel.app.
import useSWR from 'swr'
function Profile() {
const { data, error, isLoading } = useSWR('/api/user', fetcher)
if (error) return <div>failed to load</div>
if (isLoading) return <div>loading...</div>
return <div>hello {data.name}!</div>
}
In this example, the React Hook useSWR
accepts a key
and a fetcher
function.
The key
is a unique identifier of the request, normally the URL of the API. And the fetcher
accepts
key
as its parameter and returns the data asynchronously.
useSWR
also returns 3 values: data
, isLoading
and error
. When the request (fetcher) is not yet finished,
data
will be undefined
and isLoading
will be true
. When we get a response, it sets data
and error
based on the result
of fetcher
, isLoading
to false and rerenders the component.
Note that fetcher
can be any asynchronous function, you can use your favourite data-fetching
library to handle that part.
View full documentation and examples on swr.vercel.app.
This library is created by the team behind Next.js, with contributions from our community:
- Shu Ding (@shuding_) - Vercel
- Guillermo Rauch (@rauchg) - Vercel
- Joe Haddad (@timer150) - Vercel
- Paco Coursey (@pacocoursey) - Vercel
Thanks to Ryan Chen for providing the awesome swr
npm package name!
The MIT License.