映射类型

一个类型需要基于另外一个类型，但是你又不想拷贝一份，这个时候可以考虑使用映射类型

映射类型建立在索引签名的语法上

type OptionsFlags<Type> = {
  [Property in keyof Type]: boolean;
};

映射修饰符

readonly 属性只读
? 属性可选

通过前缀+-添加或删除修饰符，默认为+前缀

// 删除属性中的只读属性
type CreateMutable<Type> = {
  -readonly [Property in keyof Type]: Type[Property];
};
type LockedAccount = {
  readonly id: string;
  readonly name: string;
};
 
type UnlockedAccount = CreateMutable<LockedAccount>;

// type UnlockedAccount = {
//    id: string;
//    name: string;
// }

// 删除属性中的可选属性
type Concrete<Type> = {
  [Property in keyof Type]-?: Type[Property];
};

通过 as 实现键名重新映射

在映射类型中使用 as 语句实现键名重新映射

type MappedTypeWithNewProperties<Type> = {
    [Properties in keyof Type as NewKeyType]: Type[Properties]
}

可以利用模板字面量类型基于之前的属性名创建一个全新的属性名

type Getters<Type> = {
  [Property in keyof Type as `get${Capitalize<
    string & Property
  >}`]: () => Type[Property];
};

interface Person {
  name: string;
  age: number;
  location: string;
}

type LazyPerson = Getters<Person>;

可以遍历任何联合类型

type EventConfig<Events extends { kind: string }> = {
    [E in Events as E["kind"]]: (event: E) => void;
}
 
type SquareEvent = { kind: "square", x: number, y: number };
type CircleEvent = { kind: "circle", radius: number };
 
type Config = EventConfig<SquareEvent | CircleEvent>
// type Config = {
//    square: (event: SquareEvent) => void;
//    circle: (event: CircleEvent) => void;
// }