TypeScript:如何正确键入此`groupBy`函数

function groupBy<T, K extends keyof any>(
  array: T[],
  keySelector: (item: T) => K
): Record<K, T[]> {
  return array.reduce((acc, item) => {
    const key = keySelector(item);
    if (!acc[key]) {
      acc[key] = [];
    }
    acc[key].push(item);
    return acc;
  }, {} as Record<K, T[]>);
}

interface User {
  name: string;
  age: number;
}

const users: User[] = [
  { name: 'Alice', age: 21 },
  { name: 'Bob', age: 21 },
  { name: 'Charlie', age: 22 }
];

const groupedUsers = groupBy(users, user => user.age);

console.log(groupedUsers);
// 输出: { '21': [User, User], '22': [User] }

const groupedUsers = groupBy(users, (user): number => user.age);