TypeScript Mapped Types All in One
TypeScript Mapped Types All in One
// type Horse = {};
type OnlyBoolsAndHorses = {
// [key: string]: boolean | Horse;
[key: string]: boolean | {};
};
const conforms: OnlyBoolsAndHorses = {
del: true,
rodney: false,
};
// in keyof, Object Type ✅
type OptionsFlags<Type> = {
[Property in keyof Type]: boolean;
};
type FeatureFlags = {
darkMode: () => void;
newUserProfile: () => void;
};
type FeatureOptions = OptionsFlags<FeatureFlags>;
// Type 是对象类型
const conforms2: OptionsFlags<{}> = {
del: true,
rodney: false,
};
Mapping Modifiers
readonly
and?
-
or+
// Removes 'readonly' attributes from a type's properties
type CreateMutable<Type> = {
-readonly [Property in keyof Type]: Type[Property];
};
type LockedAccount = {
readonly id: string;
readonly name: string;
};
type UnlockedAccount = CreateMutable<LockedAccount>;
// Removes 'optional' attributes from a type's properties
type Concrete<Type> = {
[Property in keyof Type]-?: Type[Property];
};
type MaybeUser = {
id: string;
name?: string;
age?: number;
};
type User = Concrete<MaybeUser>;
as
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>;
never
// 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 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 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>;
https://www.typescriptlang.org/docs/handbook/2/mapped-types.html
refs
https://www.typescriptlang.org/docs/handbook/2/types-from-types.html
https://www.typescriptlang.org/docs/handbook/2/conditional-types.html
https://www.typescriptlang.org/docs/handbook/2/indexed-access-types.html
https://www.typescriptlang.org/docs/handbook/2/template-literal-types.html
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