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dai-shi authored Jan 7, 2025
2 parents 59879e3 + d2ac820 commit 3425802
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15 changes: 15 additions & 0 deletions docs/guides/typescript.md
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Expand Up @@ -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.
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3 changes: 1 addition & 2 deletions src/react.ts
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@@ -1,14 +1,13 @@
import React from 'react'
import { createStore } from './vanilla.ts'
import type {
ExtractState,
Mutate,
StateCreator,
StoreApi,
StoreMutatorIdentifier,
} from './vanilla.ts'

type ExtractState<S> = S extends { getState: () => infer T } ? T : never

type ReadonlyStoreApi<T> = Pick<
StoreApi<T>,
'getState' | 'getInitialState' | 'subscribe'
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2 changes: 2 additions & 0 deletions src/vanilla.ts
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Expand Up @@ -13,6 +13,8 @@ export interface StoreApi<T> {
subscribe: (listener: (state: T, prevState: T) => void) => () => void
}

export type ExtractState<S> = S extends { getState: () => infer T } ? T : never

type Get<T, K, F> = K extends keyof T ? T[K] : F

export type Mutate<S, Ms> = number extends Ms['length' & keyof Ms]
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