组件重新渲染时缓存计算的结果。
实例：count1计算斐波那契数列，count2和count1可以触发数值变化。使用memo可以使只有在count1变化时触发斐波那契数列计算函数，而count2变化时不触发斐波那契数列计算函数。
import { useMemo } from "react";import { useState } from "react";function fib(n) {console.log('计算函数执行')if (n < 3) {return 1}return fib(n - 1) + fib(n - 2)}function App() {const [count1, setCount1] = useState(0)const [count2, setCount2] = useState(0)console.log('组件重新渲染')const result = useMemo(() => {return fib(count1)}, [count1])return (<div className="App"><button onClick={() => { setCount1(count1 + 1) }}>change count1: {count1}</button><button onClick={() => { setCount2(count2 + 1) }}>change count2: {count2}</button>result: {result}</div>)}export default App
