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SWR retrieves data from cache first (stale), then sends a fetch request (revalidate) and finally returns the current data.

When React Hooks rolled out the other year, it was a big step towards making reactive user interfaces (UIs) and experiences easier. By using hooks, developers can separate logic and concerns a bit further and move more toward functional programming.

The team over at Next.js recently created a custom hook dubbed, useSWR, which stands for stale-while-revalidate. In the docs, SWR updates components continuously and automatically. UIs will always be responsive and fast.

I've already used SWR in a project for user authentication and synchronizing a dashboard with an API data source. The team behind useSWR has created documentation that makes learning to use it relatively easy. Here is a contrived, yet common example of getting started:

import useSWR from 'swr'; import { Container, Paragraph } from '@/components/system'; function Dashboard() { const { data: user, error: userError } = useSWR('/api/user', fetcher); const { data: dashboard, error: dashboardError } = useSWR( '/api/dashboard', fetcher ); if (userError || dashboardError) return <Container>failed to load</Container>; if (!user && !dashboard) return <Container>loading...</Container>; return ( <Container> <Paragraph>Hey there {user.name}!</Paragraph> </Container> //... render dashboard data ); }

Let's dig into our example code a bit.

  • We have two useSWR hook instances, each returning two values: data and error
  • The data will be undefined when the request (fetcher) has not yet completed
  • When we get a response, it sets data and error based on the result of the fetcher and re-renders the component
  • The fetcher can be any asynchronous function, so you can use your favorite data-fetching library to handle that part, like fetch or axios
  • Once we have actual data, we can render it with our Dasboard component(s)

And, voilà! We have a UI that is fast and efficient using the useSWR hook.

Learn more about useSWR at https://swr.now.sh.