2、redux源码探索 - combineReducers的实现

使用方式:

const {combineReducers} = Redux;
const rootReducer = combineReducers({
    reducer1,
    reducer2,
    reducer3,
    ...
})
//使用combineReducers的好处很明显，开发者可以按照应用状态进行分治，拆分成多个reducers，有利于开发和维护 
const store = createStore(rootReducer, preloadedState, enhancer);

const combineReducers = (reducers) => {
    return (state = {}, action) => {
        //用 Object.keys取到对应的key。这个key能从state那里取到对应的模块数据
        return Object.keys( reducers ).reduce((nextState, key) => {
            nextState[key] = reducers[key]( state[key], action );
            return nextState;
        }, {})
    }
}