createStore在redux類庫(kù)中是篇幅最長(zhǎng)的一個(gè)函數(shù)。它主要的作用是構(gòu)建redux的store。

當(dāng)createStore函數(shù)遇到enhance參數(shù)

function createStore(reducer, preloadedState, enhancer)

if (typeof enhancer !== 'undefined') {
    if (typeof enhancer !== 'function') {
      throw new Error('Expected the enhancer to be a function.')
    }

    return enhancer(createStore)(reducer, preloadedState)
  }

在createStore函數(shù)中，只要enhancer存在，創(chuàng)建store的過(guò)程將會(huì)在enhancer函數(shù)中完成。這保證了可以在enhancer函數(shù)中裝飾和包裝dispatch核心方法。有興趣可看：applyMiddleware源碼分析

dispatch函數(shù)：

 function dispatch(action) {
    if (!isPlainObject(action)) {
      throw new Error(
        'Actions must be plain objects. ' +
        'Use custom middleware for async actions.'
      )
    }

    if (typeof action.type === 'undefined') {
      throw new Error(
        'Actions may not have an undefined "type" property. ' +
        'Have you misspelled a constant?'
      )
    }

    if (isDispatching) {
      throw new Error('Reducers may not dispatch actions.')
    }
    //這就是為什么reducer函數(shù)處理返回?cái)?shù)據(jù)出現(xiàn)錯(cuò)誤也不報(bào)錯(cuò)的原因。
    //直接在dispatch函數(shù)內(nèi)進(jìn)行錯(cuò)誤處理，reducer處理action的錯(cuò)誤并不會(huì)報(bào)給開(kāi)發(fā)者。
    //（真坑爹,這導(dǎo)致開(kāi)發(fā)者很難進(jìn)行錯(cuò)誤追蹤。）
    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
  }

初始化store的state

  // 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 })

源代碼中的英文注釋，已經(jīng)說(shuō)明了這一行代碼的作用。