Consider removing `DefaultRootState` type

React-Redux v8 currently has a DefaultRootState type defined:

https://github.com/reduxjs/react-redux/blob/4d384029e3fa0355e762f40409a5dac4358a3de3/src/types.ts#L13-L23

This was copy-pasted directly from the @types/react-redux types in DefinitelyTyped, which have had that for a while.

We Redux maintainers were not involved in that type being added originally, and specifically think it’s a bad practice:

Or to say it bluntly: If at that point in time, we as Redux maintainers would have known about what was going on in DefinitelyTyped, we would have prevented DefaultRootState from ever being added. Unfortunately, at that point we were not aware.

It is a global enhancement of the state, no matter if the reducer was actually added to your store.

At one point in time, some library will go ahead and pollute that interface and suddenly every project using that library will have an extra property in their Redux store - without any reducer for it being present.

There is a good reason we don’t recommend doing this anywhere in the docs.

Given that, I’d like to propose removing it from the v8 typings before this gets released.

I’m assuming we’d want to replace that with unknown instead.

I did a couple code searches, and I see maybe 1000-1500 usages in the wild:

• https://sourcegraph.com/search?q=context:global+lang:typescript+DefaultRootState+count:2000&patternType=literal
• https://github.com/search?l=TypeScript&q=DefaultRootState&type=Code
• https://cs.github.com/?q=DefaultRootState

So that’s not zero, but it isn’t a thing that would completely break the ecosystem in the upgrade process.

Lenz also said that this is a pattern that could get replicated in userspace if desired, although I’m not sure what the details are on that.

[adamaveray]

In case anyone is looking to replicate augmenting the DefaultRootState type (to avoid having to explicitly declare the state’s type in every call to useSelector()) the following module augmentation file should work:

// react-redux.d.ts
import type { EqualityFn } from 'react-redux/es/types';
import type { GlobalState } from '...'; // Your root store type

declare module 'react-redux' {
  export declare const useSelector: <T>(selector: (state: GlobalState) => T, equalityFn?: EqualityFn<T>) => T;
}

(The file should be placed in a directory listed in the project’s tsconfig.json’s typeRoots array – see the docs)

Now calls such as useSelector(state => ...) will automatically treat the state parameter as having the above GlobalState type.

[markerikson]

Just did this in #1887 . There was also already a Connect<State = DefaultRootState> type being exported, so that just defaults to unknown now.

(That Connect type could theoretically be modified to accept a Dispatch generic too, but it looks like it would be complicated to fit in and frankly I don’t want to worry about it.)