Error encountered on `npm run dev`

Error encountered on `npm run dev`: 

```
failed to load config from .../Documents/react-query-course/vite.config.js
error when starting dev server:
Error: config must export or return an object.
```

`vite.config.js` should be updated to be an `.mjs` extension in most cases given this repo is over 3 years old. That's what worked for me.