• pureComponent

import { useState } from "react"
// useReducer,
// 統一調度
function reducer(state, action) {console.log('reducer接收參數', state, action)const { type } = actionswitch (type) {case 'add':return { num: state.num + 1 }case 'minus':return { num: state.num - 1 }}
}
function useReducer(reducer, initState) {// initState用于初始化const [state, setState] = useState(initState)const dispatch = (action) => {const newVal = reducer(state, action)setState(newVal)}return [state, dispatch]
}
export default function App() {// 參數：歸納函數，初始狀態const [state, dispatch] = useReducer(reducer, { num: 0 })return (<><p>數：{state.num}</p><button onClick={() => dispatch({ type: 'add' })}>+1</button><br /><button onClick={() => dispatch({ type: 'minus' })}>-1</button></>)
}