在Redux React Native中使用reducer时导入/导出

我正在用React Native学习Redux,我有这样一个例子:

减速机.js

import {combineReducers} from "redux"; 
import {HomeReducer as home} from "../routes/Home/modules/home";

const makeRootReducer = () => {
    return combineReducers({
        home
    });
};

export default makeRootReducer;

import {createStore, applyMiddleware, compose} from 'redux';
import thunk from "redux-thunk";
import {createLogger} from 'redux-logger';

import makeRouteReducer from './reducer';

const log = createLogger({diff: true, collapsed: true});

export default (initialState = {}) => {
    const middleware = [thunk, log];
    const enhancers = [];

    return store = createStore(
        makeRouteReducer(),
        initialState,
        compose(
            applyMiddleware(...middleware),
            ...enhancers
        )
    );
}

它很好用,但我不明白我为什么要用它 export default 在里面

当我尝试使用

// reducer.js
export makeRootReducer

// createStore.js
import {makeRouteReducer} from './reducer';

请帮我详细解释一下。

非常感谢你。