typescript-exercises（五）

一次冒险，胜过一千个安逸的日子。——保罗·科埃略《韦罗妮卡决定去死》

题目：

/*

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#partialtype
// https://www.typescriptlang.org/docs/handbook/release-notes/typescript-2-8.html#predefined-conditional-types

报错：

index.ts(101,5): error TS2345: Argument of type '{ age: number; }' is not assignable to parameter of type 'User'.
  Type '{ age: number; }' is missing the following properties from type 'User': type, name, occupation
test.ts(5,5): error TS2344: Type 'false' does not satisfy the constraint 'true'.
test.ts(11,5): error TS2344: Type 'false' does not satisfy the constraint 'true'.
test.ts(17,5): error TS2344: Type 'false' does not satisfy the constraint 'true'.
test.ts(23,5): error TS2344: Type 'false' does not satisfy the constraint 'true'.
test.ts(29,5): error TS2344: Type 'false' does not satisfy the constraint 'true'.

答案

/*

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: Partial<Omit<User, 'type'>>): User[] {
    return persons.filter(isUser).filter((user) => {
        const criteriaKeys = Object.keys(criteria) as (keyof Omit<User, 'type'>)[];
        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#partialtype
// https://www.typescriptlang.org/docs/handbook/release-notes/typescript-2-8.html#predefined-conditional-types

此处主要考察Partial<Type>的使用以及Omit<Type, Keys>的使用

Partial：基于Type里的属性构造一个类型，里面的字段全都是可选的

Omit：基于Type里的属性构造一个类型，但是删除Keys，多个的话可以这么写Omit<Todo, "completed" | "createdAt">