redux源码

使用

import { createStore } from "redux";
import { combineReducers } from 'redux';
const productsReducer = function(state=[], action) {
  return state;
}
const initialState = {
  cart: [
    {
      product: 'bread 700g',
      quantity: 2,
      unitCost: 90
    },
    {
      product: 'milk 500ml',
      quantity: 1,
      unitCost: 47
    }
  ]
}
const ADD_TO_CART = 'ADD_TO_CART';
const cartReducer = function(state=initialState, action) {
  switch (action.type) {
    case ADD_TO_CART: {
      return {
        ...state,
        cart: [...state.cart, action.payload]
      }
    }
    default:
      return state;
  }
}
function addToCart(product, quantity, unitCost) {
  return {
    type: ADD_TO_CART,
    payload: {
      product,
      quantity,
      unitCost
    }
  }
}
const allReducers = {
  products: productsReducer,
  shoppingCart: cartReducer
}
const rootReducer = combineReducers(allReducers);
let store = createStore(rootReducer);
store.dispatch(addToCart('Coffee 500gm', 1, 250));
store.dispatch(addToCart('Flour 1kg', 2, 110));
store.dispatch(addToCart('Juice 2L', 1, 250));

源码

combineReducers

export default function combineReducers(reducers: ReducersMapObject) {
  const reducerKeys = Object.keys(reducers)
  const finalReducers: ReducersMapObject = {}
  for (let i = 0; i < reducerKeys.length; i++) {
    const key = reducerKeys[i]
    if (typeof reducers[key] === 'function') {
      finalReducers[key] = reducers[key]
    }
  }
  const finalReducerKeys = Object.keys(finalReducers)

  // This is used to make sure we don't warn about the same
  // keys multiple times.
  let unexpectedKeyCache: { [key: string]: true }
  let shapeAssertionError: Error
  return function combination(
    state: StateFromReducersMapObject<typeof reducers> = {},
    action: AnyAction
  ) {
    let hasChanged = false
    const nextState: StateFromReducersMapObject<typeof reducers> = {}
    for (let i = 0; i < finalReducerKeys.length; i++) {
      const key = finalReducerKeys[i]
      const reducer = finalReducers[key]
      const previousStateForKey = state[key]
      const nextStateForKey = reducer(previousStateForKey, action)
      nextState[key] = nextStateForKey
      hasChanged = hasChanged || nextStateForKey !== previousStateForKey
    }
    hasChanged =
      hasChanged || finalReducerKeys.length !== Object.keys(state).length
    return hasChanged ? nextState : state
  }
}

createStore,dispatch

export default function createStore<
  S,
  A extends Action,
  Ext = {},
  StateExt = never
>(
  reducer: Reducer<S, A>,
  preloadedState?: PreloadedState<S> | StoreEnhancer<Ext, StateExt>,
  enhancer?: StoreEnhancer<Ext, StateExt>
): Store<ExtendState<S, StateExt>, A, StateExt, Ext> & Ext {
  let currentReducer = reducer
  let currentState = preloadedState as S
  let currentListeners: (() => void)[] | null = []
  let nextListeners = currentListeners
  let isDispatching = false
  function ensureCanMutateNextListeners() {
    if (nextListeners === currentListeners) {
      nextListeners = currentListeners.slice()
    }
  }

  function getState(): S {
    return currentState as S
  }
  function subscribe(listener: () => void) {
    let isSubscribed = true
    ensureCanMutateNextListeners()
    nextListeners.push(listener)
    return function unsubscribe() {
      if (!isSubscribed) {
        return
      }
      isSubscribed = false
      ensureCanMutateNextListeners()
      const index = nextListeners.indexOf(listener)
      nextListeners.splice(index, 1)
      currentListeners = null
    }
  }
  function dispatch(action: A) {
    try {
      isDispatching = true
      currentState = currentReducer(currentState, action)
    } finally {
      isDispatching = false
    }
    const listeners = (currentListeners = nextListeners)
    for (let i = 0; i < listeners.length; i++) {
      const listener = listeners[i]
      listener()
    }
    return action
  }
  function replaceReducer<NewState, NewActions extends A>(
    nextReducer: Reducer<NewState, NewActions>
  ): Store<ExtendState<NewState, StateExt>, NewActions, StateExt, Ext> & Ext {
    ;(currentReducer as unknown as Reducer<NewState, NewActions>) = nextReducer
    dispatch({ type: ActionTypes.REPLACE } as A)
    // change the type of the store by casting it to the new store
    return store as unknown as Store<
      ExtendState<NewState, StateExt>,
      NewActions,
      StateExt,
      Ext
    > &
      Ext
  }
  function observable() {
    const outerSubscribe = subscribe
    return {
      subscribe(observer: unknown) {
        function observeState() {
          const observerAsObserver = observer as Observer<S>
          if (observerAsObserver.next) {
            observerAsObserver.next(getState())
          }
        }
        observeState()
        const unsubscribe = outerSubscribe(observeState)
        return { unsubscribe }
      },

      [$$observable]() {
        return this
      }
    }
  }
  dispatch({ type: ActionTypes.INIT } as A)
  const store = {
    dispatch: dispatch as Dispatch<A>,
    subscribe,
    getState,
    replaceReducer,
    [$$observable]: observable
  } as unknown as Store<ExtendState<S, StateExt>, A, StateExt, Ext> & Ext
  return store
}