7 reasons why you should use SWR

Why should you use SWR?

SWR is a React Hooks library for remote 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 fetch request (revalidate), and finally comes with the up-to-date data again.

Let's see what problems SWR solves.

• Auto Revalidation: Suppose, you have opened up your todo application on two tabs. Normally, In one tab if you add a new todo then you won't see the update on the other tab. SWR solves this problem out of the box by auto re-validating. When you change your focus from the tab and then refocus again, swr will make sure the data is valid or up to date. This is done by sending another request to the API.

• Data Mutation: You can tell swr to re-validate your data with mutation. This is an example from SWR documentation. It shows how to automatically refetch the login info (e.g. inside ) when the user clicks the Logout button.
  

import useSWR, { mutate } from 'swr'function App() {    return (        <div>            <Profile />            <button                onClick={() => {                    // set the cookie as expired                    document.cookie = 'token=; expires=Thu, 01 Jan 1970 00:00:00 UTC; path=/;'                    // tell all SWRs with this key to revalidate                    mutate('/api/user')                }}            >                Logout            </button>        </div>    )}

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• Real-time experience: Suppose you want to create a todo app where you want to add a new todo. But every time you add a new item you have to refresh the page to see the changes. But with SWR mutation you can mutate the request. It simply means, when you add new data, it will automatically fetch another request and will update the UI.

• Request deduplication: Take a look at this code.
  

function useUser() {    return useSWR('/api/user', fetcher)}function Avatar() {    const { data, error } = useUser()    if (error) return <Error />    if (!data) return <Spinner />    return <img src={data.avatar_url} />}function App() {    return (        <>            <Avatar />            <Avatar />            <Avatar />            <Avatar />            <Avatar />        </>    )}

Normally it will send the same 3 requests to the API. That is unnecessary. It will take more data and will cause unnecessary rendering. Swr solves this by request deduplication. It will only send one request because they are requested at the same time. The default de-duplicating interval is 2 seconds. But you can change from the config. So it won't cause unnecessary rendering or take more data. It makes our user experience better specifically for mobile devices.

• Can be used with Both rest and graphql: SWR does not fetch the data. The fetcher function does. And that allows us to use both REST and Graphql API.

• Built-in caching support: When you first fetch data from an API endpoint it caches the response data. If you send a request to the same API then it will first give you the cached data while fetching the up-to-date data. So that you don't have to show the loading state to the user.

Reusable code: SWR is itself a hook. And you can create a custom hook from hooks. It allows us to write DRY(don't repeat yourself) code. Suppose you want to fetch data from the /users endpoint. So every time you want to fetch the data, you have to pass the fetcher function and options again and again. But if you create a custom hook then you don't have to pass anything again.

function App() {    const { data, error, isValidating } = useSWR('/users', fetcher)    return <>.... </>}// insteadfunction useUser() {    return useSWR('/users', fetcher)}function App() {    const { data, error, isValidating } = useUser()    return <>.... </>}

• Super flexible: You can configure every setting of SWR if you want. You can also set a global configuration. Read more from swr options

And these are the problems that SWR solves. It also has some other features.

• Built-in Typescript support.
• Fast, lightweight.
• Tree shaking vailable.

These are the reasons why I love SWR and you should try it too.

Shameless Plug

I have made a video about how to build a carousel postcard with React, Material-UI, and Swiper.js.
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