useRef

import React,{useRef,useEffect} from "react";


export default function App() {
  console.log("app 执行")
  const count = useRef(0)
  const [n,setN] = React.useState(0)
  const onClick = () => {
    setN(n+9)
  }
  useEffect(()=>{
    count.current += 1
    console.log(count.current)
  })
  return (
    <div className="App">
      <button onClick={onClick}>updata {n}</button>
    </div>
  );
}



//useRef  每次渲染的时候跟新一次
//为什么要用current 来确认他得知呢

// app() =>