State আপডেট করা: অবজেক্ট আর অ্যারে

function Profile() {
  const [user, setUser] = useState({ name: 'Priya', age: 21 });

  function haveBirthday() {
    user.age = user.age + 1; // mutates the existing object — DOES NOT re-render
    setUser(user);            // same reference as before, React sees no change
  }

  return <button onClick={haveBirthday}>{user.name} is {user.age}</button>;
}

function haveBirthday() {
  setUser({ ...user, age: user.age + 1 }); // a new object, one field changed
}

function TodoList() {
  const [todos, setTodos] = useState([
    { id: 1, text: 'Learn React', done: false },
  ]);

  function toggleTodo(id) {
    setTodos(todos.map((todo) =>
      todo.id === id ? { ...todo, done: !todo.done } : todo
    ));
  }

  return (
    <ul>
      {todos.map((todo) => (
        <li key={todo.id} onClick={() => toggleTodo(todo.id)}>
          {todo.done ? '✓' : '○'} {todo.text}
        </li>
      ))}
    </ul>
  );
}