Zadanie: licznik 0–20

import { useState } from 'react';

export default function Counter() {
  const [count, setCount] = useState(0);
  return <>
    <button disabled={count === 0}
      onClick={() => setCount(c => Math.max(0, c - 1))}>−</button>
    <output aria-live="polite">{count}</output>
    <button disabled={count === 20}
      onClick={() => setCount(c => Math.min(20, c + 1))}>+</button>
  </>;
}