add docs on the matter

docs/guides/typescript.md

@@ -161,6 +161,21 @@ It isn't really a lie because `{ bears: number }` is still a subtype of `{ bears
 
 Note that we don't use the curried version when using `combine` because `combine` "creates" the state. When using a middleware that creates the state, it isn't necessary to use the curried version because the state now can be inferred. Another middleware that creates state is `redux`. So when using `combine`, `redux`, or any other custom middleware that creates the state, we don't recommend using the curried version.
 
+If you want to infer state type also outside of state declaration, you can use the `ExtractState` type helper:
+
+```ts
+import { create, ExtractState } from 'zustand'
+import { combine } from 'zustand/middleware'
+
+type BearState = ExtractState<typeof useBearStore>
+
+const useBearStore = create(
+  combine({ bears: 0 }, (set) => ({
+    increase: (by: number) => set((state) => ({ bears: state.bears + by })),
+  })),
+)
+```
+
 ## Using middlewares
 
 You do not have to do anything special to use middlewares in TypeScript.