[React] #6.5 CleanUp

import { useState, useEffect } from 'react';

function Hello() {
  useEffect(function () { // 기본 버전 
    console.log("hi :)");
    return function () {
      console.log("bye :(");
    };
  }, []);
  useEffect (() => {
    console.log("hi :)");
    return () => console.log("bye :(");
  }, []);
  return <h1>Hello</h1>;
}

function App() {
  const [showing, setShowing] = useState(false);
  const onClick = () => setShowing ((prev)=> !prev);
  return (
    <div>
      {showing? <Hello /> : null}
      <button onClick={onClick}>{showing ? "Hide": "Show"}</button>  
    </div>
  );
}

export default App;