[JavaScript知识库]109.《hooks中useReducer的使用(计数器案例)》

import React, { Component, useState,useReducer,useEffect } from 'react' 

function App(){
   let useReducerData= (state,action)=>{
        switch(action){
            case "add":
                return state + 1
            case "sub":
                return state - 1
            default:
                return state
        }
     }
     let [ count,dispatch ] = useReducer(useReducerData,0)

     useEffect(() => {
         console.log("1111111");
         return () => {
            console.log("2222222"); 
         }
     }, [])
    return (
        <div>
            <h1>这是我的数字：{count}</h1>
            <button onClick={()=>{dispatch("add")}}>+1</button>
            <button onClick={()=>{dispatch("sub")}}>-1</button>
        </div>
    )
}

export default App