src/createStore.ts
import $$observable from './utils/symbol-observable'
import type {
Store,
StoreEnhancer,
Dispatch,
Observer,
ListenerCallback,
UnknownIfNonSpecific
} from './types/store'
import type { Action } from './types/actions'
import type { Reducer } from './types/reducers'
import ActionTypes from './utils/actionTypes'
import isPlainObject from './utils/isPlainObject'
import { kindOf } from './utils/kindOf'
/**
* Prevents TypeScript from inferring a generic type parameter.
*
* @template T - The type to prevent inference for.
*
* @internal
*/
type NoInfer<T> = [T][T extends any ? 0 : never]
/**
* @deprecated
*
* **We recommend using the `configureStore` method
* of the `@reduxjs/toolkit` package**, which replaces `createStore`.
*
* Redux Toolkit is our recommended approach for writing Redux logic today,
* including store setup, reducers, data fetching, and more.
*
* **For more details, please read this Redux docs page:**
* **https://redux.js.org/introduction/why-rtk-is-redux-today**
*
* `configureStore` from Redux Toolkit is an improved version of `createStore` that
* simplifies setup and helps avoid common bugs.
*
* You should not be using the `redux` core package by itself today, except for learning purposes.
* The `createStore` method from the core `redux` package will not be removed, but we encourage
* all users to migrate to using Redux Toolkit for all Redux code.
*
* If you want to use `createStore` without this visual deprecation warning, use
* the `legacy_createStore` import instead:
*
* `import { legacy_createStore as createStore} from 'redux'`
*
*/
export function createStore<
S,
A extends Action,
Ext extends {} = {},
StateExt extends {} = {}
>(
reducer: Reducer<S, A>,
enhancer?: StoreEnhancer<Ext, StateExt>
): Store<S, A, UnknownIfNonSpecific<StateExt>> & NoInfer<Ext>
/**
* @deprecated
*
* **We recommend using the `configureStore` method
* of the `@reduxjs/toolkit` package**, which replaces `createStore`.
*
* Redux Toolkit is our recommended approach for writing Redux logic today,
* including store setup, reducers, data fetching, and more.
*
* **For more details, please read this Redux docs page:**
* **https://redux.js.org/introduction/why-rtk-is-redux-today**
*
* `configureStore` from Redux Toolkit is an improved version of `createStore` that
* simplifies setup and helps avoid common bugs.
*
* You should not be using the `redux` core package by itself today, except for learning purposes.
* The `createStore` method from the core `redux` package will not be removed, but we encourage
* all users to migrate to using Redux Toolkit for all Redux code.
*
* If you want to use `createStore` without this visual deprecation warning, use
* the `legacy_createStore` import instead:
*
* `import { legacy_createStore as createStore} from 'redux'`
*
*/
export function createStore<
S,
A extends Action,
Ext extends {} = {},
StateExt extends {} = {},
PreloadedState = S
>(
reducer: Reducer<S, A, PreloadedState>,
preloadedState?: PreloadedState | undefined,
enhancer?: StoreEnhancer<Ext, StateExt>
): Store<S, A, UnknownIfNonSpecific<StateExt>> & NoInfer<Ext>
export function createStore<
S,
A extends Action,
Ext extends {} = {},
StateExt extends {} = {},
PreloadedState = S
>(
reducer: Reducer<S, A, PreloadedState>,
preloadedState?: PreloadedState | StoreEnhancer<Ext, StateExt> | undefined,
enhancer?: StoreEnhancer<Ext, StateExt>
): Store<S, A, UnknownIfNonSpecific<StateExt>> & NoInfer<Ext> {
if (typeof reducer !== 'function') {
throw new Error(
`Expected the root reducer to be a function. Instead, received: '${kindOf(
reducer
)}'`
)
}
if (
(typeof preloadedState === 'function' && typeof enhancer === 'function') ||
(typeof enhancer === 'function' && typeof arguments[3] === 'function')
) {
throw new Error(
'It looks like you are passing several store enhancers to ' +
'createStore(). This is not supported. Instead, compose them ' +
'together to a single function. See https://redux.js.org/tutorials/fundamentals/part-4-store#creating-a-store-with-enhancers for an example.'
)
}
if (typeof preloadedState === 'function' && typeof enhancer === 'undefined') {
enhancer = preloadedState as StoreEnhancer<Ext, StateExt>
preloadedState = undefined
}
if (typeof enhancer !== 'undefined') {
if (typeof enhancer !== 'function') {
throw new Error(
`Expected the enhancer to be a function. Instead, received: '${kindOf(
enhancer
)}'`
)
}
return enhancer(createStore)(
reducer,
preloadedState as PreloadedState | undefined
)
}
let currentReducer = reducer
let currentState: S | PreloadedState | undefined = preloadedState as
| PreloadedState
| undefined
let currentListeners: Map<number, ListenerCallback> | null = new Map()
let nextListeners = currentListeners
let listenerIdCounter = 0
let isDispatching = false
/**
* This makes a shallow copy of currentListeners so we can use
* nextListeners as a temporary list while dispatching.
*
* This prevents any bugs around consumers calling
* subscribe/unsubscribe in the middle of a dispatch.
*/
function ensureCanMutateNextListeners() {
if (nextListeners === currentListeners) {
nextListeners = new Map()
currentListeners.forEach((listener, key) => {
nextListeners.set(key, listener)
})
}
}
/**
* Reads the state tree managed by the store.
*
* @returns The current state tree of your application.
*/
function getState(): S {
if (isDispatching) {
throw new Error(
'You may not call store.getState() while the reducer is executing. ' +
'The reducer has already received the state as an argument. ' +
'Pass it down from the top reducer instead of reading it from the store.'
)
}
return currentState as S
}
/**
* Adds a change listener. It will be called any time an action is dispatched,
* and some part of the state tree may potentially have changed. You may then
* call `getState()` to read the current state tree inside the callback.
*
* You may call `dispatch()` from a change listener, with the following
* caveats:
*
* 1. The subscriptions are snapshotted just before every `dispatch()` call.
* If you subscribe or unsubscribe while the listeners are being invoked, this
* will not have any effect on the `dispatch()` that is currently in progress.
* However, the next `dispatch()` call, whether nested or not, will use a more
* recent snapshot of the subscription list.
*
* 2. The listener should not expect to see all state changes, as the state
* might have been updated multiple times during a nested `dispatch()` before
* the listener is called. It is, however, guaranteed that all subscribers
* registered before the `dispatch()` started will be called with the latest
* state by the time it exits.
*
* @param listener A callback to be invoked on every dispatch.
* @returns A function to remove this change listener.
*/
function subscribe(listener: () => void) {
if (typeof listener !== 'function') {
throw new Error(
`Expected the listener to be a function. Instead, received: '${kindOf(
listener
)}'`
)
}
if (isDispatching) {
throw new Error(
'You may not call store.subscribe() while the reducer is executing. ' +
'If you would like to be notified after the store has been updated, subscribe from a ' +
'component and invoke store.getState() in the callback to access the latest state. ' +
'See https://redux.js.org/api/store#subscribelistener for more details.'
)
}
let isSubscribed = true
ensureCanMutateNextListeners()
const listenerId = listenerIdCounter++
nextListeners.set(listenerId, listener)
return function unsubscribe() {
if (!isSubscribed) {
return
}
if (isDispatching) {
throw new Error(
'You may not unsubscribe from a store listener while the reducer is executing. ' +
'See https://redux.js.org/api/store#subscribelistener for more details.'
)
}
isSubscribed = false
ensureCanMutateNextListeners()
nextListeners.delete(listenerId)
currentListeners = null
}
}
/**
* Dispatches an action. It is the only way to trigger a state change.
*
* The `reducer` function, used to create the store, will be called with the
* current state tree and the given `action`. Its return value will
* be considered the **next** state of the tree, and the change listeners
* will be notified.
*
* The base implementation only supports plain object actions. If you want to
* dispatch a Promise, an Observable, a thunk, or something else, you need to
* wrap your store creating function into the corresponding middleware. For
* example, see the documentation for the `redux-thunk` package. Even the
* middleware will eventually dispatch plain object actions using this method.
*
* @param action A plain object representing “what changed”. It is
* a good idea to keep actions serializable so you can record and replay user
* sessions, or use the time travelling `redux-devtools`. An action must have
* a `type` property which may not be `undefined`. It is a good idea to use
* string constants for action types.
*
* @returns For convenience, the same action object you dispatched.
*
* Note that, if you use a custom middleware, it may wrap `dispatch()` to
* return something else (for example, a Promise you can await).
*/
function dispatch(action: A) {
if (!isPlainObject(action)) {
throw new Error(
`Actions must be plain objects. Instead, the actual type was: '${kindOf(
action
)}'. You may need to add middleware to your store setup to handle dispatching other values, such as 'redux-thunk' to handle dispatching functions. See https://redux.js.org/tutorials/fundamentals/part-4-store#middleware and https://redux.js.org/tutorials/fundamentals/part-6-async-logic#using-the-redux-thunk-middleware for examples.`
)
}
if (typeof action.type === 'undefined') {
throw new Error(
'Actions may not have an undefined "type" property. You may have misspelled an action type string constant.'
)
}
if (typeof action.type !== 'string') {
throw new Error(
`Action "type" property must be a string. Instead, the actual type was: '${kindOf(
action.type
)}'. Value was: '${action.type}' (stringified)`
)
}
if (isDispatching) {
throw new Error('Reducers may not dispatch actions.')
}
try {
isDispatching = true
currentState = currentReducer(currentState, action)
} finally {
isDispatching = false
}
const listeners = (currentListeners = nextListeners)
listeners.forEach(listener => {
listener()
})
return action
}
/**
* Replaces the reducer currently used by the store to calculate the state.
*
* You might need this if your app implements code splitting and you want to
* load some of the reducers dynamically. You might also need this if you
* implement a hot reloading mechanism for Redux.
*
* @param nextReducer The reducer for the store to use instead.
*/
function replaceReducer(nextReducer: Reducer<S, A>): void {
if (typeof nextReducer !== 'function') {
throw new Error(
`Expected the nextReducer to be a function. Instead, received: '${kindOf(
nextReducer
)}`
)
}
currentReducer = nextReducer as unknown as Reducer<S, A, PreloadedState>
// This action has a similar effect to ActionTypes.INIT.
// Any reducers that existed in both the new and old rootReducer
// will receive the previous state. This effectively populates
// the new state tree with any relevant data from the old one.
dispatch({ type: ActionTypes.REPLACE } as A)
}
/**
* Interoperability point for observable/reactive libraries.
* @returns A minimal observable of state changes.
* For more information, see the observable proposal:
* https://github.com/tc39/proposal-observable
*/
function observable() {
const outerSubscribe = subscribe
return {
/**
* The minimal observable subscription method.
* @param observer Any object that can be used as an observer.
* The observer object should have a `next` method.
* @returns An object with an `unsubscribe` method that can
* be used to unsubscribe the observable from the store, and prevent further
* emission of values from the observable.
*/
subscribe(observer: unknown) {
if (typeof observer !== 'object' || observer === null) {
throw new TypeError(
`Expected the observer to be an object. Instead, received: '${kindOf(
observer
)}'`
)
}
function observeState() {
const observerAsObserver = observer as Observer<S>
if (observerAsObserver.next) {
observerAsObserver.next(getState())
}
}
observeState()
const unsubscribe = outerSubscribe(observeState)
return { unsubscribe }
},
[$$observable]() {
return this
}
}
}
// When a store is created, an "INIT" action is dispatched so that every
// reducer returns their initial state. This effectively populates
// the initial state tree.
dispatch({ type: ActionTypes.INIT } as A)
const store = {
dispatch: dispatch as Dispatch<A>,
subscribe,
getState,
replaceReducer,
[$$observable]: observable
} as unknown as Store<S, A, StateExt> & Ext
return store
}
/**
* Creates a Redux store that holds the state tree.
*
* **We recommend using `configureStore` from the
* `@reduxjs/toolkit` package**, which replaces `createStore`:
* **https://redux.js.org/introduction/why-rtk-is-redux-today**
*
* The only way to change the data in the store is to call `dispatch()` on it.
*
* There should only be a single store in your app. To specify how different
* parts of the state tree respond to actions, you may combine several reducers
* into a single reducer function by using `combineReducers`.
*
* @param {Function} reducer A function that returns the next state tree, given
* the current state tree and the action to handle.
*
* @param {any} [preloadedState] The initial state. You may optionally specify it
* to hydrate the state from the server in universal apps, or to restore a
* previously serialized user session.
* If you use `combineReducers` to produce the root reducer function, this must be
* an object with the same shape as `combineReducers` keys.
*
* @param {Function} [enhancer] The store enhancer. You may optionally specify it
* to enhance the store with third-party capabilities such as middleware,
* time travel, persistence, etc. The only store enhancer that ships with Redux
* is `applyMiddleware()`.
*
* @returns {Store} A Redux store that lets you read the state, dispatch actions
* and subscribe to changes.
*/
export function legacy_createStore<
S,
A extends Action,
Ext extends {} = {},
StateExt extends {} = {}
>(
reducer: Reducer<S, A>,
enhancer?: StoreEnhancer<Ext, StateExt>
): Store<S, A, UnknownIfNonSpecific<StateExt>> & Ext
/**
* Creates a Redux store that holds the state tree.
*
* **We recommend using `configureStore` from the
* `@reduxjs/toolkit` package**, which replaces `createStore`:
* **https://redux.js.org/introduction/why-rtk-is-redux-today**
*
* The only way to change the data in the store is to call `dispatch()` on it.
*
* There should only be a single store in your app. To specify how different
* parts of the state tree respond to actions, you may combine several reducers
* into a single reducer function by using `combineReducers`.
*
* @param {Function} reducer A function that returns the next state tree, given
* the current state tree and the action to handle.
*
* @param {any} [preloadedState] The initial state. You may optionally specify it
* to hydrate the state from the server in universal apps, or to restore a
* previously serialized user session.
* If you use `combineReducers` to produce the root reducer function, this must be
* an object with the same shape as `combineReducers` keys.
*
* @param {Function} [enhancer] The store enhancer. You may optionally specify it
* to enhance the store with third-party capabilities such as middleware,
* time travel, persistence, etc. The only store enhancer that ships with Redux
* is `applyMiddleware()`.
*
* @returns {Store} A Redux store that lets you read the state, dispatch actions
* and subscribe to changes.
*/
export function legacy_createStore<
S,
A extends Action,
Ext extends {} = {},
StateExt extends {} = {},
PreloadedState = S
>(
reducer: Reducer<S, A, PreloadedState>,
preloadedState?: PreloadedState | undefined,
enhancer?: StoreEnhancer<Ext, StateExt>
): Store<S, A, UnknownIfNonSpecific<StateExt>> & Ext
export function legacy_createStore<
S,
A extends Action,
Ext extends {} = {},
StateExt extends {} = {},
PreloadedState = S
>(
reducer: Reducer<S, A>,
preloadedState?: PreloadedState | StoreEnhancer<Ext, StateExt> | undefined,
enhancer?: StoreEnhancer<Ext, StateExt>
): Store<S, A, UnknownIfNonSpecific<StateExt>> & Ext {
return createStore(reducer, preloadedState as any, enhancer)
}