Infer zustand store type

This package only provides type definitions and does not interfere with zustand at runtime

---

According to zustand documentation, it's impossible to infer the store type implicitly.

zustand-types utilizes an unconventional technique to correctly infer the store type both within and outside the store function. This method works perfectly under freshly released TypeScript 5, even in strict mode.

Installation

npm install -D zustand-types

yarn add -D zustand-types

Most use cases

Extract a store as a named function and provide SetState<typeof MyStore> type. That's it!

import {create} from "zustand"
import {SetState} from "zustand-types"

function MyStore(set: SetState<typeof MyStore>) {
  return {
    pets: [] as string[],
    // state: correctly inferred
    addPet: (pet: string) => set((state) => [...state.pets, pet]),
  }
}

// useStore: correctly inferred
export const useStore = create(MyStore)

Complete type signature

In case you need two other parameters, get and store, their types are also provided.

import {create} from "zustand"
import {SetState, GetState, Store} from "zustand-types"

function MyStore(
  set: SetState<typeof MyStore>,
  get: GetState<typeof MyStore>,
  store: Store<typeof MyStore>,
) {
  const state = get()
  const unsubscribe = store.subscribe((state) => {})
  return {
    //...
  }
}

export const useStore = create(MyStore)

Slice pattern

Slice pattern is a way to split your big store into multiple stores.

zustand-types provides a single type StoreArgs that captures all three arguments .

import {create} from "zustand"
import {StoreArgs} from "../src"

// Option A
function Store1(...args: StoreArgs<typeof Store1>) {
  const [set] = args
  return {
    x: 1,
    setX: (x: number) => set({x}),
  }
}

// Option B
function Store2(set: SetState<typeof Store2>, ...args: any[]) {
  return {
    y: 1,
    setY: (y: number) => set({y}),
  }
}

function Combined(...args: StoreArgs<typeof Combined>) {
  const state1 = Store1(...args)
  const state2 = Store2(...args)
  // Each slice state must be assigned to a variable, otherwise `Combined` return type will become implicit `any`.
  return {...state1, ...state2}
}

export const useStore = create(Combined)