TypeScript映射类型详情

// 当你需要提前声明属性的类型时
type OnlyBoolsAndHorses = {
  [key: string]: boolean | Horse;
};
 
const confORMs: OnlyBoolsAndHorses = {
  del: true,
  rodney: false,
};

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

type FeatureFlags = {
  darkMode: () => void;
  newUserProfile: () => void;
};
 
type FeatureOptions = OptionsFlags<FeatureFlags>;
// type FeatureOptions = {
//    darkMode: boolean;
//    newUserProfile: boolean;
// }

// 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];
};
 
type MaybeUser = {
  id: string;
  name?: string;
  age?: number;
};
 
type User = Concrete<MaybeUser>;
// type User = {
//    id: string;
//    name: string;
//    age: number;
// }

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

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>;

// type LazyPerson = {
//    getName: () => string;
//    getAge: () => number;
//    getLocation: () => string;
// }

// Remove the 'kind' property
type RemoveKindField<Type> = {
    [Property in keyof Type as Exclude<Property, "kind">]: Type[Property]
};
 
interface Circle {
    kind: "circle";
    radius: number;
}
 
type KindlessCircle = RemoveKindField<Circle>;

// type KindlessCircle = {
//    radius: number;
// }

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;
// }

type ExtractPII<Type> = {
  [Property in keyof Type]: Type[Property] extends { pii: true } ? true : false;
};
 
type DBFields = {
  id: { format: "incrementing" };
  name: { type: string; pii: true };
};
 
type ObjectsNeedingGDPRDeletion = ExtractPII<DBFields>;
// type ObjectsNeedingGDPRDeletion = {
//    id: false;
//    name: true;
// }