$ npx create-react-app learn-redux-middleware

$ cd learn-redux-middleware
$ yarn add redux react-redux

moudles/Counter.js

// 액션 타입
const INCREASE = 'INCREASE';
const DECREASE = 'DECREASE';

// 액션 생성 함수
export const increase = () => ({ type: INCREASE });
export const decrease = () => ({ type: DECREASE });

// 초깃값 (상태가 객체가 아니라 그냥 숫자여도 상관 없습니다.)
const initialState = 0;

export default function counter(state = initialState, action) {
  switch (action.type) {
    case INCREASE:
      return state + 1;
    case DECREASE:
      return state - 1;
    default:
      return state;
  }
}

루트 리듀서

modules/index.js

import { combineReducers } from 'redux';
import counter from './counter';

const rootReducer = combineReducers({ counter });

export default rootReducer;

프로젝트에 리덕스 적용

프로젝트에 리덕스를 적용 할 때는 src 디렉터리의 index.js 에서 루트리듀서를 불러와서 이를 통해

새로운 스토어를 만들고 Provider 를 사용해서 프로젝트에 적용을 해야한다.

index.js

import React from 'react';
import ReactDOM from 'react-dom';
import './index.css';
import App from './App';
import * as serviceWorker from './serviceWorker';
import { createStore } from 'redux';
import { Provider } from 'react-redux';
import rootReducer from './modules';

const store = createStore(rootReducer);

ReactDOM.render(
  <Provider store={store}>
    <App />
  </Provider>,
  document.getElementById('root')
);

카운터 컴포넌트

components/Counter.js

import React from 'react';

function Counter({ number, onIncrease, onDecrease }) {
  return (
    <div>
      <h1>{number}</h1>
      <button onClick={onIncrease}>+1</button>
      <button onClick={onDecrease}>-1</button>
    </div>
  );
}

export default Counter;

컨테이너 만들기

containers/CounterContainer.js

import React from 'react';
import Counter from '../components/Counter';
import { useSelector, useDispatch } from 'react-redux';
import { increase, decrease } from '../modules/counter';

function CounterContainer() {
  const number = useSelector(state => state.counter);
  const dispatch = useDispatch();

  const onIncrease = () => {
    dispatch(increase());
  };
  const onDecrease = () => {
    dispatch(decrease());
  };

  return (
    <Counter number={number} onIncrease={onIncrease} onDecrease={onDecrease} />
  );
}

export default CounterContainer;

개발 서버 구동

App.js