Typescript Exercises 8

Typescript Exercise 8

Exercise 8

Define type PowerUser which should have all fields from both User and Admin (except for type), and also have type ‘powerUser’ without duplicating all the fields in the code.

interface User {
  type: 'user';
  name: string;
  age: number;
  occupation: string;
}

interface Admin {
  type: 'admin';
  name: string;
  age: number;
  role: string;
}

// type needs to be specified
type PowerUser = unknown;

export type Person = User | Admin | PowerUser;

export const persons: Person[] = [
  {
    type: 'user',
    name: 'Max Mustermann',
    age: 25,
    occupation: 'Chimney sweep',
  },
  { type: 'admin', name: 'Jane Doe', age: 32, role: 'Administrator' },
  { type: 'user', name: 'Kate Müller', age: 23, occupation: 'Astronaut' },
  { type: 'admin', name: 'Bruce Willis', age: 64, role: 'World saver' },
  {
    type: 'powerUser',
    name: 'Nikki Stone',
    age: 45,
    role: 'Moderator',
    occupation: 'Cat groomer',
  },
];

function isAdmin(person: Person): person is Admin {
  return person.type === 'admin';
}

function isUser(person: Person): person is User {
  return person.type === 'user';
}

function isPowerUser(person: Person): person is PowerUser {
  return person.type === 'powerUser';
}

export function logPerson(person: Person) {
  let additionalInformation: string = '';
  if (isAdmin(person)) {
    additionalInformation = person.role;
  }
  if (isUser(person)) {
    additionalInformation = person.occupation;
  }
  if (isPowerUser(person)) {
    additionalInformation = `${person.role}, ${person.occupation}`;
  }
  console.log(`${person.name}, ${person.age}, ${additionalInformation}`);
}

console.log('Admins:');
persons.filter(isAdmin).forEach(logPerson);

console.log();

console.log('Users:');
persons.filter(isUser).forEach(logPerson);

console.log();

console.log('Power users:');
persons.filter(isPowerUser).forEach(logPerson);

How I Solved This Problem

Using Utility types in Typescript

The way of approaching is basically the same we need every properties except type property and type PowerUser need its own type which is powerUser.

1. Omit Utility Type

I used this way of approaching because, it is less code to write definitely.

then type PowerUser will be able to have all properties from type User and Admin except property type then type : powerUser is added at the end.

type PowerUser = Omit<User, 'type'> &
  Omit<Admin, 'type'> & { type: 'powerUser' };

export type Person = User | Admin | PowerUser;

2. Pick Utility Type

We can get the same result using Pick utility type as well as Omit utility type.

like below

type PowerUser = Pick<User, 'name' | 'age' | 'occupation'> &
  Pick<Admin, 'name', 'age', 'role'> & { type: 'powerUser' };

export type Person = User | Admin | PowerUser;