React experimental concurrent issue

[bbenezech]

facebook/react#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.

[bradenhs]

I'm seeing the exact same issue. Looks like this is just a warning and there isn't (as far as I can tell) anything user facing that actually breaks b/c of this. Would still be nice to see this resolved of course :)

[huozhi]

hi @bbenezech @bradenhs
I tried the experiemental build locally with suspense demo (in swr examples folder). I didn't see any warnings logging out in the console. the console tab is slient.

could you provide more details about the repro steps or the code snippet? codesandbox link will be great. and some related info like swr version. 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).

[huozhi]

@bradenhs thanks for the code example, I filed a PR to fix it. it will be released in next patch or minor version. and thanks again all of you for the reporting this issue! 👍

[huw]

@huozhi This is still occurring on 0.3.0

[jakst]

@huozhi https://codesandbox.io/s/frosty-lamarr-xzmq6 the error is still present in 0.3.8. Would you consider reopening?

[huozhi]

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

[jakst]

Works 👍 Thanks!