TypeScript utility type demos.

exclude.ts

type Dog = {
  name: string;
  race: RacesLimitedList;
};

type RacesFullList = 'Alsatian' | 'Pomeranian';
type RacesLimitedList = Exclude<RacesFullList, 'Pomeranian'>;

const dog: Dog = {
  name: 'Sam',
  race: 'Pomeranian'
};

console.log(dog);

export { };

omit.ts

type LivingBeing = {
  name: string;
  race: string;
};

// Omit only 'race' property from whichever number of properties that LivingBeing has
type Person = {
  [Property in keyof Omit<LivingBeing, 'race'>]: string;
};

const person: Person = {
  name: 'Sam'
};

console.log(person);

export { };

parameters.ts

type Dog = {
  name: string;
  race: string;
};

function makeDog(name: string, race: string): Dog {
  return {
    name,
    race
  };
}

// This will contain the parameters from the `makeDog()` function
type DogParams = Parameters<typeof makeDog>;

export { };

partial.ts

type LivingBeing<> = {
  name: string;
  race: string;
};

// Make all properties partial
type Person = Partial<LivingBeing>;

const person: Person = {};

console.log(person);

export { };

pick.ts

type Dog = {
  name: string;
  race: string;
};

// Pick out only 'name' as required property
type Person = Pick<Dog, 'name'>;

const person: Person = {
  name: 'Sam'
};

console.log(person);

export { };

required.ts

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

type Person = {
  name: string;
};

type Dog = Required<Person> & {
  race: string;
};

const dog: LivingBeing<Dog> = {
  name: 'Sam',
  race: 'Alsatian'
};

console.log(dog);

export { };

returnType.ts

type Dog = {
  name: string;
  race: string;
};

function makeDog() {
  return {
    name: 'Sam',
    race: 'Alsatian',
    city: 'Someville'
  };
}

// This will contain the return type from the `makeDog()` function
type DogReturnType = ReturnType<typeof makeDog>;

export { };