chap07 HookRef.js

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  import { useState, useRef } from 'react';
 
export default function HookRef() {
  const id = useRef(null);
  const [count, setCount] = useState(0);
 
  const handleStart = () => {
    if (id.current === null) {
      id.current = setInterval(() => setCount(c => c + 1), 1000);
    }
  };
  const handleEnd = () => {
    clearInterval(id.current);
    id.current = null;
  };
  return (
    <>
      <button onClick={handleStart}>시작</button>
      <button onClick={handleEnd}>종료</button>
      <p>{count}초 경과</p>
    </>
  );
}