React 18 in concurrent mode + Cache provider

[piotr-cz]

Bug report

Description / Observed Behavior

When using React 18 in concurrent mode and a custom cache provider, an error is thrown:

Uncaught TypeError: Cannot read properties of undefined (reading '0')
    at useSWRHandler (index.esm.js:631:1)

This happens when using create-react-app v4 or v5 in dev mode (react-scripts start), however not when running an actual build (react-scripts build).

Expected Behavior

No error is thrown

Repro Steps / Code Example

CodeSandbox based on Basic usage is available here: https://codesandbox.io/s/eager-alex-zyijly?file=/src/index.js:

1. Update react and react-dom to 18.0 or 18.1 in dependencies, enable concurrent mode (ReactDOM.createRoot(rootElement).render(...))
2. Add new provider const provider = () => new Map();
3. Wrap <App /> with <SWRConfig value={{ provider }}></SWRConfig>

Additional Context

SWR version: 1.1.0 ... 1.3.0 || 2.0.0-beta.0 || 2.0.0-beta.1
Latest version with no error: 1.0.1

It looks like the SWRGlobalState WeakMap in the useSWRHandler function doesn't contain custom cache provider, even that it has been successfully added in initCache function.

[emreycolakoglu]

Hey, this breaks us pretty bad too. Had to create a workaround using middlewares for my use-case (persistance) but it's far from perfect.
Is there a workaround?
NextJS 12.1.5
Swr 1.3.0
React 18.0.0

[piotr-cz]

Any workarounds I know of is downgrading react to v17 or swr to v1.1.
I guess this issue will receive more attention when people will start upgrading react to v18.

[shuding]

React 18 support will be our top priority for 2.0 and it’s in the works.

[promer94]

This should works in latest beta version now.
codesandbox

[piotr-cz]

@promer94
I cannot completely confirm, as upgrading swr in my sandbox to 2.0.0-beta.3 as well as downgrading in yours leads to

ModuleNotFoundError
Could not find module in path: 'swr' relative to '/src/index.js'

I have no idea what's going on

[promer94]

@piotr-cz could you try to refresh the page. I had same problem but works after reloading page. I think it might be some cache problem of codesandbox.

[piotr-cz]

@promer94
Thanks, it works!

right click into result page -> Reload Frame

[shuding]

Great! I guess we can close this issue now? 😁