<div id="root"></div>

import React from 'https://cdn.skypack.dev/react';
import ReactDOM from 'https://cdn.skypack.dev/react-dom';

const {useEffect,useState,useRef} = React; 



function Counter() {
  let [count, setCount] = useState(0);
  const countRef = useRef(count)
  
  function updateCount(newCount){
    setCount(newCount);
    countRef.current = newCount;
  }

  useEffect(() => {
    let id = setInterval(() => {
      updateCount(countRef.current + 1);
    }, 1000);
    return () => clearInterval(id);
  },[]);

  return <h1>{count}</h1>;
}

ReactDOM.render(<Counter/>,document.getElementById("root"))