注：不包含非中间件

一、源码

1.create函数返回值

create函数调用后返回useBoundStore

2.useBoundStore调用

注和原生useSyncExternalStore订阅一样

// import { useDebugValue } from 'react'
// import { useSyncExternalStoreWithSelector } from 'use-sync-external-store/shim/with-selector'
// Those don't work in ESM, because React libs are CJS only.
// See: https://github.com/pmndrs/valtio/issues/452
// The following is a workaround until ESM is supported.
// eslint-disable-next-line import/extensions
import ReactExports from 'react'
// eslint-disable-next-line import/extensions
import useSyncExternalStoreExports from 'use-sync-external-store/shim/with-selector'
import { createStore } from './vanilla.ts'
import type {
  Mutate,
  StateCreator,
  StoreApi,
  StoreMutatorIdentifier,
} from './vanilla.ts'

const { useDebugValue } = ReactExports
const { useSyncExternalStoreWithSelector } = useSyncExternalStoreExports

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

type ReadonlyStoreApi<T> = Pick<StoreApi<T>, 'getState' | 'subscribe'>

type WithReact<S extends ReadonlyStoreApi<unknown>> = S & {
  /** @deprecated please use api.getInitialState() */
  getServerState?: () => ExtractState<S>
}

let didWarnAboutEqualityFn = false

const identity = <T>(arg: T): T => arg

export function useStore<S extends WithReact<StoreApi<unknown>>>(
  api: S,
): ExtractState<S>

export function useStore<S extends WithReact<StoreApi<unknown>>, U>(
  api: S,
  selector: (state: ExtractState<S>) => U,
): U

/**
 * @deprecated The usage with three arguments is deprecated. Use `useStoreWithEqualityFn` from 'zustand/traditional'. The usage with one or two arguments is not deprecated.
 * https://github.com/pmndrs/zustand/discussions/1937
 */
export function useStore<S extends WithReact<StoreApi<unknown>>, U>(
  api: S,
  selector: (state: ExtractState<S>) => U,
  equalityFn: ((a: U, b: U) => boolean) | undefined,
): U

export function useStore<TState, StateSlice>(
  api: WithReact<StoreApi<TState>>,
  selector: (state: TState) => StateSlice = identity as any,
  equalityFn?: (a: StateSlice, b: StateSlice) => boolean,
) {
  if (
    import.meta.env?.MODE !== 'production' &&
    equalityFn &&
    !didWarnAboutEqualityFn
  ) {
    console.warn(
      "[DEPRECATED] Use `createWithEqualityFn` instead of `create` or use `useStoreWithEqualityFn` instead of `useStore`. They can be imported from 'zustand/traditional'. https://github.com/pmndrs/zustand/discussions/1937",
    )
    didWarnAboutEqualityFn = true
  }
  const slice = useSyncExternalStoreWithSelector(
    api.subscribe,
    api.getState,
    api.getServerState || api.getInitialState,
    selector,
    equalityFn,
  )
  useDebugValue(slice)
  return slice
}

export type UseBoundStore<S extends WithReact<ReadonlyStoreApi<unknown>>> = {
  (): ExtractState<S>
  <U>(selector: (state: ExtractState<S>) => U): U
  /**
   * @deprecated Use `createWithEqualityFn` from 'zustand/traditional'
   */
  <U>(
    selector: (state: ExtractState<S>) => U,
    equalityFn: (a: U, b: U) => boolean,
  ): U
} & S

type Create = {
  <T, Mos extends [StoreMutatorIdentifier, unknown][] = []>(
    initializer: StateCreator<T, [], Mos>,
  ): UseBoundStore<Mutate<StoreApi<T>, Mos>>
  <T>(): <Mos extends [StoreMutatorIdentifier, unknown][] = []>(
    initializer: StateCreator<T, [], Mos>,
  ) => UseBoundStore<Mutate<StoreApi<T>, Mos>>
  /**
   * @deprecated Use `useStore` hook to bind store
   */
  <S extends StoreApi<unknown>>(store: S): UseBoundStore<S>
}

const createImpl = <T>(createState: StateCreator<T, [], []>) => {
  if (
    import.meta.env?.MODE !== 'production' &&
    typeof createState !== 'function'
  ) {
    console.warn(
      "[DEPRECATED] Passing a vanilla store will be unsupported in a future version. Instead use `import { useStore } from 'zustand'`.",
    )
  }
  const api =
    typeof createState === 'function' ? createStore(createState) : createState

  const useBoundStore: any = (selector?: any, equalityFn?: any) =>
    useStore(api, selector, equalityFn)

  Object.assign(useBoundStore, api)

  return useBoundStore
}

export const create = (<T>(createState: StateCreator<T, [], []> | undefined) =>
  createState ? createImpl(createState) : createImpl) as Create

/**
 * @deprecated Use `import { create } from 'zustand'`
 */
export default ((createState: any) => {
  if (import.meta.env?.MODE !== 'production') {
    console.warn(
      "[DEPRECATED] Default export is deprecated. Instead use `import { create } from 'zustand'`.",
    )
  }
  return create(createState)
}) as Create

二、函数解析

1.create

type Create = {
  <T, Mos extends [StoreMutatorIdentifier, unknown][] = []>(
    initializer: StateCreator<T, [], Mos>,
  ): UseBoundStore<Mutate<StoreApi<T>, Mos>>
  <T>(): <Mos extends [StoreMutatorIdentifier, unknown][] = []>(
    initializer: StateCreator<T, [], Mos>,
  ) => UseBoundStore<Mutate<StoreApi<T>, Mos>>
  /**
   * @deprecated Use `useStore` hook to bind store
   */
  <S extends StoreApi<unknown>>(store: S): UseBoundStore<S>
}

const createImpl = <T>(createState: StateCreator<T, [], []>) => {
  if (
    import.meta.env?.MODE !== 'production' &&
    typeof createState !== 'function'
  ) {
    console.warn(
      "[DEPRECATED] Passing a vanilla store will be unsupported in a future version. Instead use `import { useStore } from 'zustand'`.",
    )
  }
  // createStore是生成api
  //  export interface StoreApi<T> {
  //    setState: SetStateInternal<T>
  //    getState: () => T
  //    getInitialState: () => T
  //    subscribe: (listener: (state: T, prevState: T) => void) => () => void
  //    /**
  //     * @deprecated Use `unsubscribe` returned by `subscribe`
  //     */
  //    destroy: () => void
  //  }
  const api =
    typeof createState === 'function' ? createStore(createState) : createState

  const useBoundStore: any = (selector?: any, equalityFn?: any) =>
    useStore(api, selector, equalityFn)
  // useBoundStore合并api相关属性
  Object.assign(useBoundStore, api)

  return useBoundStore
}

export const create = (<T>(createState: StateCreator<T, [], []> | undefined) =>
  createState ? createImpl(createState) : createImpl) as Create

2.createStore

type SetStateInternal<T> = {
  _(
    partial: T | Partial<T> | { _(state: T): T | Partial<T> }['_'],
    replace?: boolean | undefined,
  ): void
}['_']

export interface StoreApi<T> {
  setState: SetStateInternal<T>
  getState: () => T
  getInitialState: () => T
  subscribe: (listener: (state: T, prevState: T) => void) => () => void
  /**
   * @deprecated Use `unsubscribe` returned by `subscribe`
   */
  destroy: () => void
}

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

export type Mutate<S, Ms> = number extends Ms['length' & keyof Ms]
  ? S
  : Ms extends []
    ? S
    : Ms extends [[infer Mi, infer Ma], ...infer Mrs]
      ? Mutate<StoreMutators<S, Ma>[Mi & StoreMutatorIdentifier], Mrs>
      : never

export type StateCreator<
  T,
  Mis extends [StoreMutatorIdentifier, unknown][] = [],
  Mos extends [StoreMutatorIdentifier, unknown][] = [],
  U = T,
> = ((
  setState: Get<Mutate<StoreApi<T>, Mis>, 'setState', never>,
  getState: Get<Mutate<StoreApi<T>, Mis>, 'getState', never>,
  store: Mutate<StoreApi<T>, Mis>,
) => U) & { $$storeMutators?: Mos }

// eslint-disable-next-line @typescript-eslint/no-unused-vars, @typescript-eslint/no-empty-interface
export interface StoreMutators<S, A> {}
export type StoreMutatorIdentifier = keyof StoreMutators<unknown, unknown>

type CreateStore = {
  <T, Mos extends [StoreMutatorIdentifier, unknown][] = []>(
    initializer: StateCreator<T, [], Mos>,
  ): Mutate<StoreApi<T>, Mos>

  <T>(): <Mos extends [StoreMutatorIdentifier, unknown][] = []>(
    initializer: StateCreator<T, [], Mos>,
  ) => Mutate<StoreApi<T>, Mos>
}

type CreateStoreImpl = <
  T,
  Mos extends [StoreMutatorIdentifier, unknown][] = [],
>(
  initializer: StateCreator<T, [], Mos>,
) => Mutate<StoreApi<T>, Mos>
// createStore实现，典型的发布订阅模式
const createStoreImpl: CreateStoreImpl = (createState) => {
  type TState = ReturnType<typeof createState>
  type Listener = (state: TState, prevState: TState) => void
  let state: TState
  const listeners: Set<Listener> = new Set()
  // 设置值更新Snapshot
  const setState: StoreApi<TState>['setState'] = (partial, replace) => {
    // TODO: Remove type assertion once https://github.com/microsoft/TypeScript/issues/37663 is resolved
    // https://github.com/microsoft/TypeScript/issues/37663#issuecomment-759728342
    const nextState =
      typeof partial === 'function'
        // partial调用会传之前state作为入参
        ? (partial as (state: TState) => TState)(state)
        : partial
    if (!Object.is(nextState, state)) {
      const previousState = state
      state =
        replace ?? (typeof nextState !== 'object' || nextState === null)
          ? (nextState as TState)
          : Object.assign({}, state, nextState)
      // 执行订阅函数
      listeners.forEach((listener) => listener(state, previousState))
    }
  }
  // 获取Snapshot
  const getState: StoreApi<TState>['getState'] = () => state
  // 初始状态Snapshot
  const getInitialState: StoreApi<TState>['getInitialState'] = () =>
    initialState
  // 订阅函数
  const subscribe: StoreApi<TState>['subscribe'] = (listener) => {
    listeners.add(listener)
    // Unsubscribe
    // 组件卸载是触发取消订阅
    return () => listeners.delete(listener)
  }
  // 可以手动触发取消订阅
  const destroy: StoreApi<TState>['destroy'] = () => {
    if (import.meta.env?.MODE !== 'production') {
      console.warn(
        '[DEPRECATED] The `destroy` method will be unsupported in a future version. Instead use unsubscribe function returned by subscribe. Everything will be garbage-collected if store is garbage-collected.',
      )
    }
    listeners.clear()
  }
  // api包含上面方法
  const api = { setState, getState, getInitialState, subscribe, destroy }
  // 执行了createState函数（create函数的入参）
  const initialState = (state = createState(setState, getState, api))
  return api as any
}

export const createStore = ((createState) =>
  createState ? createStoreImpl(createState) : createStoreImpl) as CreateStore

/**
 * @deprecated Use `import { createStore } from 'zustand/vanilla'`
 */
export default ((createState) => {
  if (import.meta.env?.MODE !== 'production') {
    console.warn(
      "[DEPRECATED] Default export is deprecated. Instead use import { createStore } from 'zustand/vanilla'.",
    )
  }
  return createStore(createState)
}) as CreateStore

// ---------------------------------------------------------

/**
 * @deprecated Use `unknown` instead of `State`
 */
export type State = unknown

/**
 * @deprecated Use `Partial<T> | ((s: T) => Partial<T>)` instead of `PartialState<T>`
 */
export type PartialState<T extends State> =
  | Partial<T>
  | ((state: T) => Partial<T>)

/**
 * @deprecated Use `(s: T) => U` instead of `StateSelector<T, U>`
 */
export type StateSelector<T extends State, U> = (state: T) => U

/**
 * @deprecated Use `(a: T, b: T) => boolean` instead of `EqualityChecker<T>`
 */
export type EqualityChecker<T> = (state: T, newState: T) => boolean

/**
 * @deprecated Use `(state: T, previousState: T) => void` instead of `StateListener<T>`
 */
export type StateListener<T> = (state: T, previousState: T) => void

/**
 * @deprecated Use `(slice: T, previousSlice: T) => void` instead of `StateSliceListener<T>`.
 */
export type StateSliceListener<T> = (slice: T, previousSlice: T) => void

/**
 * @deprecated Use `(listener: (state: T) => void) => void` instead of `Subscribe<T>`.
 */
export type Subscribe<T extends State> = {
  (listener: (state: T, previousState: T) => void): () => void
}

/**
 * @deprecated You might be looking for `StateCreator`, if not then
 * use `StoreApi<T>['setState']` instead of `SetState<T>`.
 */
export type SetState<T extends State> = {
  _(
    partial: T | Partial<T> | { _(state: T): T | Partial<T> }['_'],
    replace?: boolean | undefined,
  ): void
}['_']

/**
 * @deprecated You might be looking for `StateCreator`, if not then
 * use `StoreApi<T>['getState']` instead of `GetState<T>`.
 */
export type GetState<T extends State> = () => T

/**
 * @deprecated Use `StoreApi<T>['destroy']` instead of `Destroy`.
 */
export type Destroy = () => void

3.useStore

let didWarnAboutEqualityFn = false

const identity = <T>(arg: T): T => arg

export function useStore<S extends WithReact<StoreApi<unknown>>>(
  api: S,
): ExtractState<S>

export function useStore<S extends WithReact<StoreApi<unknown>>, U>(
  api: S,
  selector: (state: ExtractState<S>) => U,
): U

/**
 * @deprecated The usage with three arguments is deprecated. Use `useStoreWithEqualityFn` from 'zustand/traditional'. The usage with one or two arguments is not deprecated.
 * https://github.com/pmndrs/zustand/discussions/1937
 */
export function useStore<S extends WithReact<StoreApi<unknown>>, U>(
  api: S,
  selector: (state: ExtractState<S>) => U,
  equalityFn: ((a: U, b: U) => boolean) | undefined,
): U

export function useStore<TState, StateSlice>(
  api: WithReact<StoreApi<TState>>,
  selector: (state: TState) => StateSlice = identity as any,
  equalityFn?: (a: StateSlice, b: StateSlice) => boolean,
) {
  if (
    import.meta.env?.MODE !== 'production' &&
    equalityFn &&
    !didWarnAboutEqualityFn
  ) {
    console.warn(
      "[DEPRECATED] Use `createWithEqualityFn` instead of `create` or use `useStoreWithEqualityFn` instead of `useStore`. They can be imported from 'zustand/traditional'. https://github.com/pmndrs/zustand/discussions/1937",
    )
    didWarnAboutEqualityFn = true
  }
  // 调用useSyncExternalStoreWithSelector
  const slice = useSyncExternalStoreWithSelector(
    api.subscribe,
    api.getState,
    api.getServerState || api.getInitialState,
    selector,
    equalityFn,
  )
  useDebugValue(slice)
  return slice
}