Package description
The swr npm package is a React Hooks library for remote data fetching. The name 'SWR' is derived from stale-while-revalidate, a HTTP cache invalidation strategy popularized by HTTP RFC 5861. SWR is a strategy to first return the data from cache (stale), then send the fetch request (revalidate), and finally come with the up-to-date data.
Data Fetching
SWR provides a hook called useSWR for data fetching. You can pass a key and a fetcher function, and it will return the data, error, and other useful values for handling the UI state.
import useSWR from 'swr'
function Profile() {
const { data, error } = useSWR('/api/user', fetcher)
if (error) return <div>Failed to load</div>
if (!data) return <div>Loading...</div>
return <div>Hello, {data.name}!</div>
}Automatic Revalidation
SWR automatically revalidates data when a user focuses on the window or when the network is reconnected. It can also be configured to revalidate data at a fixed interval.
import useSWR from 'swr'
function Profile() {
const { data } = useSWR('/api/user', fetcher, {
refreshInterval: 3000
})
// data will be revalidated every 3 seconds
return <div>{data.name}</div>
}Local Mutation
SWR allows you to mutate the local data immediately and revalidate it in the background. This provides an optimistic UI update experience.
import useSWR, { mutate } from 'swr'
function updateUsername(name) {
mutate('/api/user', { ...data, name }, false)
fetch('/api/user', {
method: 'POST',
body: JSON.stringify({ name })
}).then(() => {
mutate('/api/user')
})
}React Query is another library for fetching, caching, and updating data in React applications. It provides more advanced features like query cancellation, background fetching, and even pagination helpers. React Query is often compared to SWR for its similar use cases but offers a different API and additional features.
Apollo Client is a comprehensive state management library for JavaScript that enables you to manage both local and remote data with GraphQL. It is more complex and powerful than SWR, designed specifically for GraphQL, and provides features like caching, optimistic UI, and subscription support.
Axios is a promise-based HTTP client for the browser and Node.js. While it is not a hook-based data fetching library like SWR, it is often used for making HTTP requests in React applications. Developers would use Axios for fetching data and then manage the caching and state themselves or with additional libraries.
Readme
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:
...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:
Thanks to Ryan Chen for providing the awesome swr npm package name!
The MIT License.
FAQs
React Hooks library for remote data fetching
The npm package swr receives a total of 1,854,976 weekly downloads. As such, swr popularity was classified as popular.
We found that swr demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago. It has 8 open source maintainers collaborating on the project.
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