useMemo使用场景：消耗非常大的计算，例如递归

import {  useMemo, useState } from 'react';
// 缓存：消耗非常大的计算，例如递归
function fib(n){
  console.log('fib');
  if(n < 3)
    return 1;
  return fib(n-2) + fib(n-1);
}

const App = () => {
  const [count1,setCount1] = useState(0);
  const [count2,setCount2] = useState(0);
  
  const result = useMemo(()=>{
    return fib(count1)
  },[count1])
  // const result = fib(count1);
  console.log('组件重新渲染了');
  return (
    <div className="home">
      <button type="primary" onClick={()=>setCount1(count1 + 1)}>count1值{count1}</button><br />
      <button type="primary" onClick={()=>setCount2(count2 + 1)}>count2值{count2}</button><br />
      {result}
    </div>
  )
}

export default App