Ex 5

문제

/*

Intro:

    Time to filter the data! In order to be flexible
    we filter users using a number of criteria and
    return only those matching all of the criteria.
    We don't need Admins yet, we only filter Users.

Exercise:

    Without duplicating type structures, modify
    filterUsers function definition so that we can
    pass only those criteria which are needed,
    and not the whole User information as it is
    required now according to typing.

Higher difficulty bonus exercise:

    Exclude "type" from filter criteria.

*/

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);

// In case you are stuck:
// https://www.typescriptlang.org/docs/handbook/utility-types.html
// https://www.typescriptlang.org/docs/handbook/release-notes/typescript-2-8.html#predefined-conditional-types

풀이

filterUsers 함수는 주어진 배열에서 조건을 필터링해 원하는 요소만 남기는 함수다.

Partial을 사용해 주어진 타입에서 원하는 프로퍼티만을 사용한다.

export function filterUsers(persons: Person[], criteria: Partial<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];
        });
    });
}