TypeScript Helpers

helpers.ts

// -- Unwrapping values from an array inside an interface --

type Person = {
  name: string;
  birthDate?: string;
  age: number;
  hobbies: Array<{ title: string; location: string }>
}

type DeArrayify<A> = A extends Array<infer T> ? T : A;
type Hobby = DeArrayify<Person['hobbies']>;
// Hobby = { title: string, location: string }

// -- Unwrapping template values from interfaces with knockout Observable values --

type Person2 = {
  name: string;
  birthDate?: string;
  age: ko.Observable<number>;
}

type UnwrapObservable<I> = {
  [K in keyof I]: I[K] extends ko.Observable ? I[K] extends ko.Observable<infer U> ? U : never : I[K];
};

type Unwrapped = UnwrapObservable<Person2>;
// Unwrapped = { name: string, birthDate?: string; age: number; }