React experimental concurrent issue

https://github.com/facebook/react/pull/18838

I tried swr with suspense mode, with a recent 0.0.0-experimental-7f28234f8 react build, and I get errors Can't perform a React state update on a component that hasn't mounted yet for each useSWR call.

This indicates that there’s a side-effect spawned during render, that then asynchronously tries to set state when the response comes back. E.g. kick off a request and then setState with the result. It’s a common mistake when implementing Suspense.

This should be done in useEffect.

Does this make sense to you?

Unfortunately I can’t help you a lot more than that, it doesn’t help to where the error comes exactly.

[huozhi]

@huw @Jakst 0.3.9 should fix this issue. could you bump version to try again? thanks!

[bradenhs]

Here’s a codesandbox link: https://codesandbox.io/s/quirky-burnell-cn51p?file=/src/App.tsx. The problem only appears when there are multiple useSWR hooks used. Also, the warning doesn’t appear on the initial load of the page. You have to refresh the codesandbox preview specifically for some reason (I’m guessing that’s a codesandbox specific issue though since locally I see the warning on the initial load).