Describe inferring RootState type from store.getState

The docs show inferring type RootState = ReturnType<typeof rootReducer>. But, if you pass the slice reducers directly to configureStore(), you never created the root reducer yourself, so you need to infer it as type RootState = ReturnType<typeof store.getState> instead.

We should update the Advanced Tutorial and Usage with TypeScript pages to mention that.

See https://stackoverflow.com/a/59827580/62937 for an example of this

[lucassus]

@msutkowski Thank you very much! You saved me quite a few hours of debugging 😉 It seems that in my case it was a problem with the reducer builder. For example instead of builder => builder.addCase(...), I should have builder => { builder.addCase(...) }.

@markerikson Why in this case these brackets are so important? Is the typing system somehow relies on the return value form the builder?

[amankkg]

Such changes would conflict with this advice from docs on getDefaultMiddleware<RootState> https://redux-starter-kit.js.org/usage/usage-with-typescript#correct-typings-for-the-dispatch-type

const store = configureStore({
  reducer: rootReducer,
  middleware: [
    ...customMiddleware,
    ...getDefaultMiddleware<RootState>(),
  ] as const,
})

// Type alias 'RootState' circularly references itself. ts(2456)
export type RootState = ReturnType<typeof store.getState>