SWR 2.0 on its way! Check https://github.com/vercel/swr/releases/tag/2.0.0-beta.0 for the previous 2.0 beta updates.

💖 Give feedback in discussion: #1932.

Highlights

New isLoading state (#1928)

Previously, useSWR only returns a isValidating state, which is an indicator of both initial requests and automatic & manual revalidations. It includes polling requests and focus revalidations, etc.

But if you need to display an initial skeleton while loading the data, you will have to do something like

const isLoading = typeof data === 'undefined' && !error

...which is a popular pattern in the community. In this case, isValidating doesn't help much.

In this release, useSWR, useSWRInfinite and useSWRImmutable will return an extra isLoading state along with the isValidating state. They will fit to different scenarios:

function Stock() {
  const { data, isLoading, isValidating } = useSWR(STOCK_API, fetcher, {
    refreshInterval: 3000
  });

  // If it's still loading the initial data, there is nothing to display.
  // We return a skeleton here.
  if (isLoading) return <div className="skeleton" />;

  // Otherwise, display the data and a spinner that indicates a background
  // revalidation.
  return (
    <>
      <div>AAPL ${data}</div>
      {isValidating ? <div className="spinner" /> : null}
    </>
  );
}

In the example above, we display a skeleton while loading the data. After the data is loaded, we show a spinner next to the data whenever we are re-fetching (revalidating):

You can find the full code for this example here: https://codesandbox.io/s/swr-isloading-v8dfpy.

New keepPreviousData option (#1929)

When doing data fetching based on continuous user actions, e.g. real-time search when typing, keeping the previous fetched data can improve the UX a lot.

In SWR 2.0, there is now a keepPreviousData option to enable that behavior. Here's a simple search UI:

function Search() {
  const [search, setSearch] = React.useState('');

  const { data, isLoading } = useSWR(`/search?q=${search}`, fetcher, {
    keepPreviousData: true
  });

  return (
    <div>
      <input
        type="text"
        value={search}
        onChange={(e) => setSearch(e.target.value)}
        placeholder="Search..."
      />

      <div className={isLoading ? "loading" : ""}>
        {data?.products.map(item => <Product key={item.id} name={item.name} />)
      </div>
    </div>
  );
}

With keepPreviousData enabled, you will still get the previous data even if you change the SWR key and the data for the new key starts loading again. This improves the visual continuity quite a lot, the search feels smoother after flipping the switch:

You can find the full code for this example here: https://codesandbox.io/s/swr-keeppreviousdata-fsjz3m.

Breakings

Type InfiniteFetcher is renamed to SWRInfiniteFetcher (#1930)

This type was already marked as deprecated in 1.x, and it now removed in this beta. If you are using it, please do the following change:

- import { InfiniteFetcher } from 'swr/infinite'
+ import { SWRInfiniteFetcher } from 'swr/infinite'

What's Changed

• breaking: drop legacy types by @huozhi in #1930
• feat: isLoading state and refactor the core by @shuding in #1928
• feat: keepPreviousData option by @shuding in #1929
• chore: refactoring by @shuding in #1925
• fix: output mutation cjs bundle with named exports by @huozhi in #1926

Full Changelog: 2.0.0-beta.0...2.0.0-beta.1