[Redux/Mobx] 说说Redux的实现流程

通过分析redux的几个核心api，来看如何实现redux

store.subscribe: 订阅数据的变化
store.dispatch：dispatch后改变state,同时通知store.subscribe函数执行，上面这两个函数可以利用发布-订阅模式
store.getState: 通过这个函数直接返回内存中的state变量即可
简单的实现如下

export function createStore(reducer, enhancer) {if (enhancer && typeof enhancer === 'function') {const newCreateStore = enhancer(createStore);const newStore = newCreateStore(reducer);return newStore;}let state;              // state记录所有状态let listeners = [];     // 保存所有注册的回调function subscribe(callback) {listeners.push(callback);       // subscribe就是将回调保存下来}// dispatch就是将所有的回调拿出来依次执行就行function dispatch(action) {state = reducer(state, action);for (let i = 0; i < listeners.length; i++) {const listener = listeners[i];listener();}}// getState直接返回statefunction getState() {return state;}// store包装一下前面的方法直接返回const store = {subscribe,dispatch,getState}return store;
}export function combineReducers(reducerMap) {const reducerKeys = Object.keys(reducerMap);    // 先把参数里面所有的键值拿出来// 返回值是一个普通结构的reducer函数const reducer = (state = {}, action) => {const newState = {};for (let i = 0; i < reducerKeys.length; i++) {// reducerMap里面每个键的值都是一个reducer，我们把它拿出来运行下就可以得到对应键新的state值// 然后将所有reducer返回的state按照参数里面的key组装好// 最后再返回组装好的newState就行const key = reducerKeys[i];const currentReducer = reducerMap[key];const prevState = state[key];newState[key] = currentReducer(prevState, action);}return newState;};return reducer;
}// 参数支持多个中间件
export function applyMiddleware(...middlewares) {function enhancer(createStore) {function newCreateStore(reducer) {const store = createStore(reducer);// 多个middleware，先解构出dispatch => newDispatch的结构const chain = middlewares.map(middleware => middleware(store));const { dispatch } = store;// 用compose得到一个组合了所有newDispatch的函数const newDispatchGen = Redux.compose(...chain);// 执行这个函数得到newDispatchconst newDispatch = newDispatchGen(dispatch);return {...store, dispatch: newDispatch}}return newCreateStore;}return enhancer;}