useState 除了直接给定初始值，还可以通过函数返回值的形式为状态赋初始值

const [value, setValue] = useState(() => 返回值);

例如

const App: React.FC = () => {
  
  const [count] = useState(() => {
    **const date = new Date();
    return { year: date.getFullYear(), month: date.getMonth() + 1, day: date.getDate() }**
  });
  
  return (
    <div>
      <h1>Year: {count.year}</h1>
      <h1>Month: {count.month}</h1>
      <h1>Day: {count.day}</h1>
    </div>
  );
};

export default App;