Readonly 所有属性值转换为只读的

把数组或对象的所有属性值转换为只读的，这就意味着这些属性不能被重新赋值。

interface Person {
  name: string;
  age: number;
  gender?: "male" | "female";
}
let p: Readonly<Person> = {
  name: "hello",
  age: 10,
  gender: "male",
};
p.age = 11; // error  Cannot assign to 'age' because it is a read-only property.