[React 19] useEffect does not re-fire on hot reload with React 19 and vite

[gkiely]

In prior versions of react, saving a file will trigger the components useEffect hooks to run. This does not work for react 19.
This applies to both @vitejs/plugin-react-swc and @vitejs/plugin-react

Repo: https://github.com/gkiely/swc-issue

Steps to reproduce:

• npm i
• npm run dev
• open repo and press save in App.tsx
• console.log will not fire after pressing save
• npm i react@latest react-dom@latest (installs latest react 18)
• npm run dev
• press save in App.tsx
• console.log will fire

Video reproduction:
https://www.loom.com/share/b493602e3f7244d2948c5bb871531881?sid=c9bdec15-5b87-4375-a659-6c63804cb032

Notes:
I previously opened a ticket here but it is perhaps an issue with react 19: vitejs/vite-plugin-react#335

[prafulla-codes]

Hey @gkiely -
I'd like to work on this issue

[ArnaudBarre]

I've looked into it and this happen only with StrictMode enabled.

[eps1lon]

Does this work in React 18?

[ArnaudBarre]

Yep, React with 18 useEffect runs everytime if the file is updated

[eps1lon]

Can reproduce with the provided repro and also [email protected]. I also double checked by using breakpoints to ensure it's not just console.log being incorrectly silenced.