Managing Remote Data with SWR

In this series, instead of using a state-management library or proposing a one-size-fits-all solution, we start from the bare minimum and we build up our state management as we need it.

• In the first article we described how we load and display data with hooks.
• In the second article we learned how to change remote data with hooks.
• In the third article we learned how to share data between components with React Context, without using globals, singletons or resorting to state management libraries like MobX or Redux.
• In this fourth article we'll see how to share data between using SWR, which is probably what we should have done from the beginning.

In the previous articles we were storing the loaded data within React, in a useState hook. But since then SWR was released (Oct 2019).

I first learned about SWR thanks to a video tutorial by Leigh Halliday: "React Data Fetching with Hooks using SWR", and I thought it was interesting enough that I could try it on a small internal project at work.

But a few weeks later a Twitter thread took me to this article; something clicked in my head and I realised I wasn't just looking for an excuse to try SWR.

No. I had been doing it wrong all along!

I was storing my remotely fetched data in useReducer or useState and manually mutating (or via a reducer), and then maybe reloading from the server in some cases, but not in others. And I was using React Context to make the data available to unrelated components in my app.

SWR makes this easier and better.

SWR stores the fetched data in a static cache. Therefore there's no need to use React Context to share the data with other components. And all components fetching the same data are updated when the data changes.

I refactored my SPA to use SWR and that resulted in a much simpler application logic. In addition, we now benefit from all the nice features that come with SWR such as "focus revalidation" and "refetch on interval".

Let's refactor our example from the previous three articles to use SWR.

Before SWR

Our demo app before SWR is what we got after our third article. (see repo)

Install SWR

yarn add swr

Refactoring our custom hook

In our demo app we have a custom useFetchedGames hook that loads the games using the useAsyncFunction hook, and then stores them using useState to provida a way to locally mutate the data.

const useFetchedGames = () => {
  const [fetchedGames, error, isPending] = useAsyncFunction(getGames, emptyList);

  const [games, setGames] = React.useState(emptyList);
  React.useEffect(() => {
    setGames(fetchedGames);
  }, [fetchedGames]);

  return { games, setGames, error, isPending };
};

The problem with this approach is:

1. The list of games is stored twice: first in a useState hook inside useAsyncFunction, and then in a new useState hook.
2. If the list of games is updated on the server, we never reload it. Here's where SWR shines.

We're going to refactor useFetchedGames to use SWR instead of useState.

const useFetchedGames = () => {
  const { data, error, mutate } = useSWR('getGames', getGames); 

  const games = data || []
  const isPending = !data
  const setGames = mutate

  return { games, setGames, error, isPending };
};

The full diff can be found in this git commit.

Note the "getGames" string literal, just before the getGames function. This is a key to help SWR identify our request. In our case it can be anything as long as it is unique for this resource (the list of games). There's a even simpler way. You can find it in the docs.

Removing React Context

Now that we're using useSWR we don't need a React context, its provider, nor the useContext hook.

In the demo project we make our components consume the useGames hook directly, instead of the useGamesContext one.

For example, GameGrid.tsx:

- import { useGamesContext } from '../GamesContext';
+ import { useGames } from '../useGames';

  export const GameGrid = () => {
-   const { games, error, isPending, markAsFinished } = useGamesContext();
+   const { games, error, isPending, markAsFinished } = useGames();

    return (
      <div className="gamegrid">

You can see the complete diff in this git commit.

Conclusion

With this small refactoring, our app has less code to maintain and we benefit from other great SWR features:

• Revalidate on focus.
• Revalidate on interval. (optional)
• Revalidate on reconnect.
• Retry on error.

I think Zeit's SWR (or a similar library) is a much better solution than storing fetched data in a React component using useState or useReducer.

I continue to store my application's UI state using custom hooks that use useReducer and useState but for remote data, I prefer to store it in a cache.

Please let me know what you think in the comments below.