TypeError: Cannot read properties of null (reading 'useContext')

[dolie]

• Check if updating to the latest Preact version resolves the issue

Describe the bug
Hello,

I'm not able to run Preact components using SWR, in a test environnement.
In dev/prod environnement Preact handles perfectly SWR, but not in test environnement.
When I launch the test, it returns the error :
TypeError: Cannot read properties of null (reading 'useContext')

To Reproduce

Barebone example : https://github.com/dolie/preact-swr-vitest-bug

Steps to reproduce the behavior:

1. git clone git@github.com:dolie/preact-swr-vitest-bug.git
2. pnpm i
3. pnpm vitest

Expected behavior
Preact handles SWR in a test environnement, as it is running in dev/prod environnement.

Additional Context

SWR
Vitest
MSW
Testing-library

[JoviDeCroock]

As your stacktrace sugggests this error is happening in react.development.js which means that you are trying to import useContext from React rather than Preact. I don't think this bug belongs here, it might be due to preset vite but def not on the core repo

[rschristian]

Vitest unfortunately has problems aliasing, this is something we've seen a few times. For reference, vitest-dev/vitest#5004, vitest-dev/vitest#4365 (comment), potentially vitest-dev/vitest#1910

I think this is something Vitest needs to address, not us here.

[dolie]

Thank you for you fast answer !

Ok, so I added preact/compat using pnpm aliases, but it throws a new error about useSyncExternalStore ?

[rschristian]

That error says you're loading multiple copies of Preact at once; hooks, in both Preact and React, require that the library is loaded as singleton (only once).

Probably the dual-package hazard: vitest-dev/vitest#4365. Again, something that unfortunately needs to be addressed in Vitest (as far as I am aware).

[dolie]

Vitest team found a workaround😉
I updated the repo with it.
Thank you for your help @rschristian @JoviDeCroock 🙏