Javascript/react/redux

reduxを使ったプロジェクト作成

npx create-react-app helloredux
cd helloredux
npm install redux react-redux

追加js

src/reducers/counter.js

const initialState = {
  count: 0
}

const counter = (state = initialState, action) => {
  switch (action.type) {
    case 'INCREMENT':
      return { ...state, count: state.count + 1 }
    case 'DECREMENT':
      return { ...state, count: state.count - 1 }
    default:
      return state
  }
}

export default counter

src/store.js

import { createStore } from 'redux'
import counter from './reducers/counter'

const store = createStore(counter)

export default store

src/index.js

import React from 'react';
import ReactDOM from 'react-dom/client';
import './index.css';
import App from './App';
import reportWebVitals from './reportWebVitals';

import { Provider } from 'react-redux'
import store from './store'

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

// 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();

src/App.js

import React from 'react'
import { useSelector, useDispatch } from 'react-redux'

function App() {
  const count = useSelector((state) => state.count)
  const dispatch = useDispatch()

  const increment = () => dispatch({ type: 'INCREMENT' })
  const decrement = () => dispatch({ type: 'DECREMENT' })

  return (
    <div>
      <h1>カウント: {count}</h1>
      <button onClick={increment}>+1</button>
      <button onClick={decrement}>-1</button>
    </div>
  )
}

export default App

参考

https://gizanbeak.com/post/react-redux-tutorial