前端 - ts 中 in keyof 的怎么用？

Question

下面这一段 TS 代码是什么意思，如果我把 T 传入 Animal 类型，Simplify 的类型是什么样子的？仍然是跟 Animal 一样的类型吗？

interface Animal {
  name: string;
  age: number;
}
type Simplify<T> = {
  [P in keyof T]: T[P];
};

Answer 1

补了一下示例，看看？

interface Animal {
  name: string;
  age: number;
}
type Simplify<T> = {
  [P in keyof T]: T[P];
};

type Simplify2<T> = {
  [P in keyof T]?: T[P];
};

type SimplifyAnimal = Simplify<Animal>;

type SimplifyAnimal2 = Simplify2<Animal>;

const a: Animal = {
  name: 'dog',
  age: 2,
}

const b: SimplifyAnimal = a;

const c: SimplifyAnimal2 = {
  name: 'dog',
}