Node.jsがインストール済であること

yarn add redux react-redux

これでまずreduxを使用できるようにすること

Action

• JavaScriptのオブジェクトのこと
• type　:　typeに対応する値
• typeの値はユニークでなければならない

// ActionCreater 
// Componentで使用される

export const INCREMENT = "INCREMENT"
export const DECREMENT = "DECREMENT"

export const increment = () => ({
    type: INCREMENT
})

export const decrement = () => ({
    type: DECREMENT
})

Reducer

• Actionに組み込まれているTypeに応じてどう状態を変化させるのかと言うことを定義するもの

import {INCREMENT, DECREMENT} from "../Actions/"

const initialState = {value: 0}

export default(state = initialState, action) => {
    switch(action.type){
        case INCREMEMT: 
            return {value: state.value + 1};
        case DECREMENT:
            return {alue: state.value - 1}
    }
}

Store

import React from 'react';
import ReactDOM from 'react-dom';
import {createStore} from 'redux';
import {Provider} from 'react-redux';
import './index.css';
import App from './Components/App';
import reducer from 'Reducers';
import reportWebVitals from './reportWebVitals';

const store = createStore(reducer)

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

// If you want to start measuring performance in your app, pass a function
// to log results (for example: reportWebVitals(console.log))
// or send to an analytics endpoint. Learn more: <https://bit.ly/CRA-vitals>
reportWebVitals();

import {createStore} from 'redux';
import {Provider} from 'react-redux';
import reducer from 'Reducers';

上記import後、

const store = createStore(reducer)

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

createStoreメソッドを使用