Typescript Exercise 풀이

Typescript Exercise 풀이하러 가기
타입스크립트 오류를 해결해보며 학습할 수 있는 Typescript Exercise 사이트입니다.
풀이를 작성해보았습니다.

풀이

1번

문제

export type User = unknown;

export const users: unknown[] = [
  {
    name: "Max Mustermann",
    age: 25,
    occupation: "Chimney sweep",
  },
  {
    name: "Kate Müller",
    age: 23,
    occupation: "Astronaut",
  },
];

export function logPerson(user: unknown) {
  console.log(` - ${user.name}, ${user.age}`);
}

console.log("Users:");
users.forEach(logPerson);

풀이

export interface User {
    name: string;
    age: number;
    occupation : string;
};

export const users: User[] = [
    {
        name: 'Max Mustermann',
        age: 25,
        occupation: 'Chimney sweep'
    },
    {
        name: 'Kate Müller',
        age: 23,
        occupation: 'Astronaut'
    }
];

export function logPerson(user: User) {
    console.log(` - ${user.name}, ${user.age}`);
}

console.log('Users:');
users.forEach(logPerson);

풀이방법

우선 User 의 타입을 unknown으로 선언해 있는 상태여서 타입에러가 났었다. User가 객체타입이니 interface로 알맞는 타입으로 선언해주었다.

2번

문제

interface User {
    name: string;
    age: number;
    occupation: string;
}

interface Admin {
    name: string;
    age: number;
    role: string;
}

export type Person = unknown;

export const persons: User[] /* <- Person[] */ = [
    {
        name: 'Max Mustermann',
        age: 25,
        occupation: 'Chimney sweep'
    },
    {
        name: 'Jane Doe',
        age: 32,
        role: 'Administrator'
    },
    {
        name: 'Kate Müller',
        age: 23,
        occupation: 'Astronaut'
    },
    {
        name: 'Bruce Willis',
        age: 64,
        role: 'World saver'
    }
];

export function logPerson(user: User) {
    console.log(` - ${user.name}, ${user.age}`);
}

persons.forEach(logPerson);

풀이

interface User {
    name: string;
    age: number;
    occupation: string;
}

interface Admin {
    name: string;
    age: number;
    role: string;
}

export type Person = User | Admin;

export const persons: Person[] = [
    {
        name: 'Max Mustermann',
        age: 25,
        occupation: 'Chimney sweep'
    },
    {
        name: 'Jane Doe',
        age: 32,
        role: 'Administrator'
    },
    {
        name: 'Kate Müller',
        age: 23,
        occupation: 'Astronaut'
    },
    {
        name: 'Bruce Willis',
        age: 64,
        role: 'World saver'
    }
];

export function logPerson(user: Person) {
    console.log(` - ${user.name}, ${user.age}`);
}

persons.forEach(logPerson);

풀이방법

persons 배열은 User 와 Admin 타입이 같이 존재한 배열이여서 User와 Admin의 합집합인 Person을 정의해 주었다. 이에 쓰인 |은 유니온타입이라고 한다.

3번

문제

interface User {
    name: string;
    age: number;
    occupation: string;
}

interface Admin {
    name: string;
    age: number;
    role: string;
}

export type Person = User | Admin;

export const persons: Person[] = [
    {
        name: 'Max Mustermann',
        age: 25,
        occupation: 'Chimney sweep'
    },
    {
        name: 'Jane Doe',
        age: 32,
        role: 'Administrator'
    },
    {
        name: 'Kate Müller',
        age: 23,
        occupation: 'Astronaut'
    },
    {
        name: 'Bruce Willis',
        age: 64,
        role: 'World saver'
    }
];

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

persons.forEach(logPerson);

풀이

interface User {
    name: string;
    age: number;
    occupation: string;
}

interface Admin {
    name: string;
    age: number;
    role: string;
}

export type Person = User | Admin;

export const persons: Person[] = [
    {
        name: 'Max Mustermann',
        age: 25,
        occupation: 'Chimney sweep'
    },
    {
        name: 'Jane Doe',
        age: 32,
        role: 'Administrator'
    },
    {
        name: 'Kate Müller',
        age: 23,
        occupation: 'Astronaut'
    },
    {
        name: 'Bruce Willis',
        age: 64,
        role: 'World saver'
    }
];

export function logPerson(person: Person) {
    let additionalInformation: string;
    if ("role" in person) {
        additionalInformation = person.role;
    } else {
        additionalInformation = person.occupation;
    }
    console.log(` - ${person.name}, ${person.age}, ${additionalInformation}`);
}

persons.forEach(logPerson);

풀이방법

타입가드 문제였다. 타입가드는 조건문 안에서 타임범위를 한정시켜줄수 있는 방법인데, Person이 유니온타입으로 공통된속성에만 접근할 수 있다보니 role, occupation에 접근할수 없는 에러가 나왔다.
타입가드 방법은 많은데,그 중 in을 사용하여 role이 객체 내부에 존재한지 조건문을 수정했다.

4번

문제

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

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

export type Person = User | Admin;

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' }
];

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

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

export function logPerson(person: Person) {
    let additionalInformation: string = '';
    if (isAdmin(person)) {
        additionalInformation = person.role;
    }
    if (isUser(person)) {
        additionalInformation = 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);

풀이

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

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

export type Person = User | Admin;

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' }
];

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

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

export function logPerson(person: Person) {
    let additionalInformation: string = '';
    if (isAdmin(person)) {
        additionalInformation = person.role;
    }
    if (isUser(person)) {
        additionalInformation = 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);

풀이방법

원래 풀었던 방법은 조건문을 person.type === admin으로 수정하여서 해결하였지만 답안을 보니 문제의도가 사용자 정의 타입가드에 대한 문제였다. 사용자 정의 타입가드는 어떤 인자명은 어떠한 타입이다 라는 값을 리턴하는 함수이다.is를 사용하여 타입가드를 해줄 수 있었다.

5번

문제

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

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

export type Person = User | Admin;

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: 'user',
        name: 'Wilson',
        age: 23,
        occupation: 'Ball'
    },
    {
        type: 'admin',
        name: 'Agent Smith',
        age: 23,
        role: 'Administrator'
    }
];

export const isAdmin = (person: Person): person is Admin => person.type === 'admin';
export const isUser = (person: Person): person is User => person.type === 'user';

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

export function filterUsers(persons: Person[], criteria: User): User[] {
    return persons.filter(isUser).filter((user) => {
        const criteriaKeys = Object.keys(criteria) as (keyof User)[];
        return criteriaKeys.every((fieldName) => {
            return user[fieldName] === criteria[fieldName];
        });
    });
}

console.log('Users of age 23:');

filterUsers(
    persons,
    {
        age: 23
    }
).forEach(logPerson);

풀이

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

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

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

export type Person = User | Admin;

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: 'user',
        name: 'Wilson',
        age: 23,
        occupation: 'Ball'
    },
    {
        type: 'admin',
        name: 'Agent Smith',
        age: 23,
        role: 'Administrator'
    }
];

export const isAdmin = (person: Person): person is Admin => person.type === 'admin';
export const isUser = (person: Person): person is User => person.type === 'user';

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

export function filterUsers(persons: Person[], criteria: OptiionalUser): User[] {
    return persons.filter(isUser).filter((user) => {
        const criteriaKeys = Object.keys(criteria) as (keyof OptiionalUser)[];
        return criteriaKeys.every((fieldName) => {
            return user[fieldName] === criteria[fieldName];
        });
    });
}

console.log('Users of age 23:');

filterUsers(
    persons,
    {
        age: 23
    }
).forEach(logPerson);

풀이방법

이 문제도 답안과 다르게 오류를 해결했는데... 프로퍼티를 다 안받고 넘길수 있는 타입이 필요해서 전체 optional인 타입을 새로 만들어주었다. 답안은 Partial<Omit<User, 'type'>>을 criteria에 타입정의를 해줌으로써 해결하였다. 이를 유틸리티 타입이라고 하는데 Parial은 특정 타입의 부분 집합을 만족하는 타입을 정의할 수 있다. Omit은 특정속성만 제거한 타입을 정의해서 type을 제거해주었다.

6번

문제

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

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

export type Person = User | Admin;

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: 'user', name: 'Wilson', age: 23, occupation: 'Ball' },
    { type: 'admin', name: 'Agent Smith', age: 23, role: 'Anti-virus engineer' }
];

export function logPerson(person: Person) {
    console.log(
        ` - ${person.name}, ${person.age}, ${person.type === 'admin' ? person.role : person.occupation}`
    );
}

export function filterPersons(persons: Person[], personType: string, criteria: Partial<Omit<Person, 'type'>>): unknown[] {
    return persons
        .filter((person) => person.type === personType)
        .filter((person) => {
            let criteriaKeys = Object.keys(criteria) as (keyof Person)[];
            return criteriaKeys.every((fieldName) => {
                return person[fieldName] === criteria[fieldName];
            });
        });
}

export const usersOfAge23 = filterPersons(persons, 'user', { age: 23 });
export const adminsOfAge23 = filterPersons(persons, 'admin', { age: 23 });

console.log('Users of age 23:');
usersOfAge23.forEach(logPerson);

console.log();

console.log('Admins of age 23:');
adminsOfAge23.forEach(logPerson);

6번은 답안을 봐도 잘 이해가 안가서 다시 풀어보려 한다ㅠ

7번

문제

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

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

function logUser(user: User) {
    const pos = users.indexOf(user) + 1;
    console.log(` - #${pos} User: ${user.name}, ${user.age}, ${user.occupation}`);
}

function logAdmin(admin: Admin) {
    const pos = admins.indexOf(admin) + 1;
    console.log(` - #${pos} Admin: ${admin.name}, ${admin.age}, ${admin.role}`);
}

const admins: Admin[] = [
    {
        type: 'admin',
        name: 'Will Bruces',
        age: 30,
        role: 'Overseer'
    },
    {
        type: 'admin',
        name: 'Steve',
        age: 40,
        role: 'Steve'
    }
];

const users: User[] = [
    {
        type: 'user',
        name: 'Moses',
        age: 70,
        occupation: 'Desert guide'
    },
    {
        type: 'user',
        name: 'Superman',
        age: 28,
        occupation: 'Ordinary person'
    }
];

export function swap<T, U>(v1: T, v2: U): [U, T] {
    return [v2, v1];
}

function test1() {
    console.log('test1:');
    const [secondUser, firstAdmin] = swap(admins[0], users[1]);
    logUser(secondUser);
    logAdmin(firstAdmin);
}

function test2() {
    console.log('test2:');
    const [secondAdmin, firstUser] = swap(users[0], admins[1]);
    logAdmin(secondAdmin);
    logUser(firstUser);
}

function test3() {
    console.log('test3:');
    const [secondUser, firstUser] = swap(users[0], users[1]);
    logUser(secondUser);
    logUser(firstUser);
}

function test4() {
    console.log('test4:');
    const [firstAdmin, secondAdmin] = swap(admins[1], admins[0]);
    logAdmin(firstAdmin);
    logAdmin(secondAdmin);
}

function test5() {
    console.log('test5:');
    const [stringValue, numericValue] = swap(123, 'Hello World');
    console.log(` - String: ${stringValue}`);
    console.log(` - Numeric: ${numericValue}`);
}

[test1, test2, test3, test4, test5].forEach((test) => test());

풀이

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

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

function logUser(user: User) {
    const pos = users.indexOf(user) + 1;
    console.log(` - #${pos} User: ${user.name}, ${user.age}, ${user.occupation}`);
}

function logAdmin(admin: Admin) {
    const pos = admins.indexOf(admin) + 1;
    console.log(` - #${pos} Admin: ${admin.name}, ${admin.age}, ${admin.role}`);
}

const admins: Admin[] = [
    {
        type: 'admin',
        name: 'Will Bruces',
        age: 30,
        role: 'Overseer'
    },
    {
        type: 'admin',
        name: 'Steve',
        age: 40,
        role: 'Steve'
    }
];

const users: User[] = [
    {
        type: 'user',
        name: 'Moses',
        age: 70,
        occupation: 'Desert guide'
    },
    {
        type: 'user',
        name: 'Superman',
        age: 28,
        occupation: 'Ordinary person'
    }
];

export function swap<T, V>(v1: T, v2: V): [V, T] {
    return [v2, v1];
}

function test1() {
    console.log('test1:');
    const [secondUser, firstAdmin] = swap(admins[0], users[1]);
    logUser(secondUser);
    logAdmin(firstAdmin);
}

function test2() {
    console.log('test2:');
    const [secondAdmin, firstUser] = swap(users[0], admins[1]);
    logAdmin(secondAdmin);
    logUser(firstUser);
}

function test3() {
    console.log('test3:');
    const [secondUser, firstUser] = swap(users[0], users[1]);
    logUser(secondUser);
    logUser(firstUser);
}

function test4() {
    console.log('test4:');
    const [firstAdmin, secondAdmin] = swap(admins[1], admins[0]);
    logAdmin(firstAdmin);
    logAdmin(secondAdmin);
}

function test5() {
    console.log('test5:');
    const [stringValue, numericValue] = swap(123, 'Hello World');
    console.log(` - String: ${stringValue}`);
    console.log(` - Numeric: ${numericValue}`);
}

[test1, test2, test3, test4, test5].forEach((test) => test());

풀이방법

제네릭 문제였다. 제네릭은 타입을 함수의 파라미터처럼 사용할 수 있다. 그래서 swap()함수에서 v1으로 무엇이 들어오든 v2 위치로 바꿔줄 수 있다.

8번

문제

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

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

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);

풀이

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

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

interface PowerUser {
    type: 'powerUser';
    name: string;
    age: number;
    occupation: string;
    role: string;
};

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);

풀이방법

unknown 인 PowerUser 타입을 선언해주었다.
답안을 보니 나는 좀 무식하게 선언을 해준것 같고 type PowerUser = Omit<User, 'type'> & Omit<Admin, 'type'> & { type: 'powerUser' }; 로 유틸리티 타입와 &연산자로 해결할 수 있는 문제이다.

9번

문제

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

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

type Person = User | Admin;

const admins: Admin[] = [
    { type: 'admin', name: 'Jane Doe', age: 32, role: 'Administrator' },
    { type: 'admin', name: 'Bruce Willis', age: 64, role: 'World saver' }
];

const users: User[] = [
    { type: 'user', name: 'Max Mustermann', age: 25, occupation: 'Chimney sweep' },
    { type: 'user', name: 'Kate Müller', age: 23, occupation: 'Astronaut' }
];

export type ApiResponse<T> = unknown;

type AdminsApiResponse = (
    {
        status: 'success';
        data: Admin[];
    } |
    {
        status: 'error';
        error: string;
    }
);

export function requestAdmins(callback: (response: AdminsApiResponse) => void) {
    callback({
        status: 'success',
        data: admins
    });
}

type UsersApiResponse = (
    {
        status: 'success';
        data: User[];
    } |
    {
        status: 'error';
        error: string;
    }
);

export function requestUsers(callback: (response: UsersApiResponse) => void) {
    callback({
        status: 'success',
        data: users
    });
}

export function requestCurrentServerTime(callback: (response: unknown) => void) {
    callback({
        status: 'success',
        data: Date.now()
    });
}

export function requestCoffeeMachineQueueLength(callback: (response: unknown) => void) {
    callback({
        status: 'error',
        error: 'Numeric value has exceeded Number.MAX_SAFE_INTEGER.'
    });
}

function logPerson(person: Person) {
    console.log(
        ` - ${person.name}, ${person.age}, ${person.type === 'admin' ? person.role : person.occupation}`
    );
}

function startTheApp(callback: (error: Error | null) => void) {
    requestAdmins((adminsResponse) => {
        console.log('Admins:');
        if (adminsResponse.status === 'success') {
            adminsResponse.data.forEach(logPerson);
        } else {
            return callback(new Error(adminsResponse.error));
        }

        console.log();

        requestUsers((usersResponse) => {
            console.log('Users:');
            if (usersResponse.status === 'success') {
                usersResponse.data.forEach(logPerson);
            } else {
                return callback(new Error(usersResponse.error));
            }

            console.log();

            requestCurrentServerTime((serverTimeResponse) => {
                console.log('Server time:');
                if (serverTimeResponse.status === 'success') {
                    console.log(`   ${new Date(serverTimeResponse.data).toLocaleString()}`);
                } else {
                    return callback(new Error(serverTimeResponse.error));
                }

                console.log();

                requestCoffeeMachineQueueLength((coffeeMachineQueueLengthResponse) => {
                    console.log('Coffee machine queue length:');
                    if (coffeeMachineQueueLengthResponse.status === 'success') {
                        console.log(`   ${coffeeMachineQueueLengthResponse.data}`);
                    } else {
                        return callback(new Error(coffeeMachineQueueLengthResponse.error));
                    }

                    callback(null);
                });
            });
        });
    });
}

startTheApp((e: Error | null) => {
    console.log();
    if (e) {
        console.log(`Error: "${e.message}", but it's fine, sometimes errors are inevitable.`)
    } else {
        console.log('Success!');
    }
});

풀이

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

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

type Person = User | Admin;

const admins: Admin[] = [
    { type: 'admin', name: 'Jane Doe', age: 32, role: 'Administrator' },
    { type: 'admin', name: 'Bruce Willis', age: 64, role: 'World saver' }
];

const users: User[] = [
    { type: 'user', name: 'Max Mustermann', age: 25, occupation: 'Chimney sweep' },
    { type: 'user', name: 'Kate Müller', age: 23, occupation: 'Astronaut' }
];

export type ApiResponse<T> = { status: 'success'; data: T; } | { status: 'error'; error: string; };;

export function requestAdmins(callback: (response: ApiResponse<Admin[]>) => void) {
    callback({
        status: 'success',
        data: admins
    });
}

type UsersApiResponse = (
    {
        status: 'success';
        data: User[];
    } |
    {
        status: 'error';
        error: string;
    }
);



export function requestUsers(callback: (response: UsersApiResponse) => void) {
    callback({
        status: 'success',
        data: users
    });
}

export function requestCurrentServerTime(callback: (response: ApiResponse<number>) => void) {
    callback({
        status: 'success',
        data: Date.now()
    });
}

export function requestCoffeeMachineQueueLength(callback: (response: ApiResponse<number>) => void) {
    callback({
        status: 'error',
        error: 'Numeric value has exceeded Number.MAX_SAFE_INTEGER.'
    });
}

function logPerson(person: Person) {
    console.log(
        ` - ${person.name}, ${person.age}, ${person.type === 'admin' ? person.role : person.occupation}`
    );
}

function startTheApp(callback: (error: Error | null) => void) {
    requestAdmins((adminsResponse) => {
        console.log('Admins:');
        if (adminsResponse.status === 'success') {
            adminsResponse.data.forEach(logPerson);
        } else {
            return callback(new Error(adminsResponse.error));
        }

        console.log();

        requestUsers((usersResponse) => {
            console.log('Users:');
            if (usersResponse.status === 'success') {
                usersResponse.data.forEach(logPerson);
            } else {
                return callback(new Error(usersResponse.error));
            }

            console.log();

            requestCurrentServerTime((serverTimeResponse) => {
                console.log('Server time:');
                if (serverTimeResponse.status === 'success') {
                    console.log(`   ${new Date(serverTimeResponse.data).toLocaleString()}`);
                } else {
                    return callback(new Error(serverTimeResponse.error));
                }

                console.log();

                requestCoffeeMachineQueueLength((coffeeMachineQueueLengthResponse) => {
                    console.log('Coffee machine queue length:');
                    if (coffeeMachineQueueLengthResponse.status === 'success') {
                        console.log(`   ${coffeeMachineQueueLengthResponse.data}`);
                    } else {
                        return callback(new Error(coffeeMachineQueueLengthResponse.error));
                    }

                    callback(null);
                });
            });
        });
    });
}

startTheApp((e: Error | null) => {
    console.log();
    if (e) {
        console.log(`Error: "${e.message}", but it's fine, sometimes errors are inevitable.`)
    } else {
        console.log('Success!');
    }
});

풀이방법

ApiResponse 의 타입이 unknown으로 되어있는걸 보고 타입 선언 부터 해주었다. success 의 data의 타입이 달라지니 제네릭을 써야하겠다 생각했고 error는 그대로 string을 유지한 ApiResponse을 선언해서 이용해 문제를 풀 수 있었다.