終極版的applyMiddleware

Question

我的問題的實施是爲什麼middlewareAPI不能使用：

const middlewareAPI = { 
    getState: store.getState, 
    dispatch: dispatch 
} 

在下面的源代碼替換定義：

export default function applyMiddleware(...middlewares) { 
    return (createStore) => (reducer, preloadedState, enhancer) => { 
    const store = createStore(reducer, preloadedState, enhancer) 
    let dispatch = store.dispatch 
    let chain = [] 

    const middlewareAPI = { 
     getState: store.getState, 
     dispatch: (...args) => dispatch(...args) // why not just use `dispatch: dispatch` 
    } 
    chain = middlewares.map(middleware => middleware(middlewareAPI)) 
    dispatch = compose(...chain)(store.dispatch) 

    return { 
     ...store, 
     dispatch 
    } 
    } 
} 

任何人都可以告訴我有什麼區別？謝謝。

Answer 1

這是一個JS變量範圍/託管的複雜組合，需要確保傳入的調度方法實際上指向中間件鏈的開始。

有關更多詳細信息，請參閱新增（並未發佈）Redux FAQ entry on why applyMiddleware uses a closure。