type-challenges

学习typscript的开源仓库
地址：https://github.com/type-challenges/type-challenges

warm-up

下方题目列表为热身题，总数量为1

13.helloworld

Hello, World!

在Type Challenges，我们使用类型系统自身来实现自动判题`

在这个挑战中，你需要修改下方的代码使得测试通过（没有类型错误）

// expected to be string
type HelloWorld = any
// you should make this work
type test = Expect<Equal<HelloWorld, string>>

// expected to be string
type HelloWorld = any
// you should make this work
type test = Expect<Equal<HelloWorld, string>>

解答

type HelloWorld = string

type HelloWorld = string

easy

下方题目列表为简单题，总数量为13

4.pick

实现 TS 内置的 Pick<T, K>，但不可以使用它

从类型 T 中选择出属性 K，构造成一个新的类型

举个例子

interface Todo {
  title: string
  description: string
  completed: boolean
}

type TodoPreview = MyPick<Todo, 'title' | 'completed'>

const todo: TodoPreview = {
    title: 'Clean room',
    completed: false,
}

interface Todo {
  title: string
  description: string
  completed: boolean
}

type TodoPreview = MyPick<Todo, 'title' | 'completed'>

const todo: TodoPreview = {
    title: 'Clean room',
    completed: false,
}

解答

type MyPick<T, K extends keyof T> = {
  [key in K]: T[key]
}

type MyPick<T, K extends keyof T> = {
  [key in K]: T[key]
}

7.Readonly

不要使用内置的Readonly<T>，自己实现一个

该 Readonly 会接收一个 泛型参数，并返回一个完全一样的类型，只是所有属性都会被 readonly 所修饰

也就是不可以再对该对象的属性赋值

例如：

interface Todo {
  title: string
  description: string
}

const todo: MyReadonly<Todo> = {
  title: "Hey",
  description: "foobar"
}

todo.title = "Hello" // Error: cannot reassign a readonly property
todo.description = "barFoo" // Error: cannot reassign a readonly property

interface Todo {
  title: string
  description: string
}

const todo: MyReadonly<Todo> = {
  title: "Hey",
  description: "foobar"
}

todo.title = "Hello" // Error: cannot reassign a readonly property
todo.description = "barFoo" // Error: cannot reassign a readonly property

解答

type MyReadonly<T> = {
  readonly [K in keyof T] : T[K]
}

type MyReadonly<T> = {
  readonly [K in keyof T] : T[K]
}

11.Tuple to Object

传入一个元组类型，将这个元组类型转换为对象类型，这个对象类型的键/值都是从元组中遍历出来

例如：

const tuple = ['tesla', 'model 3', 'model X', 'model Y'] as const

type result = TupleToObject<typeof tuple> // expected { tesla: 'tesla', 'model 3': 'model 3', 'model X': 'model X', 'model Y': 'model Y'}

const tuple = ['tesla', 'model 3', 'model X', 'model Y'] as const

type result = TupleToObject<typeof tuple> // expected { tesla: 'tesla', 'model 3': 'model 3', 'model X': 'model X', 'model Y': 'model Y'}

解答

type TupleToObject<T extends readonly any[]> = {
  [P in T[number]]: P
}

type TupleToObject<T extends readonly any[]> = {
  [P in T[number]]: P
}

14.First of Array

实现一个通用First<T>，它接受一个数组T并返回它的第一个元素的类型。

例如：

type arr1 = ['a', 'b', 'c']
type arr2 = [3, 2, 1]

type head1 = First<arr1> // expected to be 'a'
type head2 = First<arr2> // expected to be 3

type arr1 = ['a', 'b', 'c']
type arr2 = [3, 2, 1]

type head1 = First<arr1> // expected to be 'a'
type head2 = First<arr2> // expected to be 3

解答

type First<T extends any[]> = T extends [] ? never : T[0]
type First<T extends any[]> = T['length'] extends 0 ? never : T[0]
type First<T extends any[]> = T[0] extends T[number] ? T[0] : never
type First<T extends any[]> = T extends [infer First, ...unknown[]] ? First : never
type First<T extends any[]> = T extends [infer First,...infer Other] ? First : never

type First<T extends any[]> = T extends [] ? never : T[0]
type First<T extends any[]> = T['length'] extends 0 ? never : T[0]
type First<T extends any[]> = T[0] extends T[number] ? T[0] : never
type First<T extends any[]> = T extends [infer First, ...unknown[]] ? First : never
type First<T extends any[]> = T extends [infer First,...infer Other] ? First : never

18.Length of Tuple

创建一个通用的Length，接受一个readonly的数组，返回这个数组的长度

例如：

type tesla = ['tesla', 'model 3', 'model X', 'model Y']
type spaceX = ['FALCON 9', 'FALCON HEAVY', 'DRAGON', 'STARSHIP', 'HUMAN SPACEFLIGHT']

type teslaLength = Length<tesla> // expected 4
type spaceXLength = Length<spaceX> // expected 5

type tesla = ['tesla', 'model 3', 'model X', 'model Y']
type spaceX = ['FALCON 9', 'FALCON HEAVY', 'DRAGON', 'STARSHIP', 'HUMAN SPACEFLIGHT']

type teslaLength = Length<tesla> // expected 4
type spaceXLength = Length<spaceX> // expected 5

解答

type Length<T extends readonly any[]> = T['length']

type Length<T extends readonly any[]> = T['length']

43.Exclude

实现内置的Exclude <T, U>类型，但不能直接使用它本身。

从联合类型T中排除U的类型成员，来构造一个新的类型

解答

type MyExclude<T, U> = T extends U ? never : T

type MyExclude<T, U> = T extends U ? never : T

189.Awaited

假如我们有一个 Promise 对象，这个 Promise 对象会返回一个类型。在 TS 中，我们用 Promise 中的 T 来描述这个 Promise 返回的类型。请你实现一个类型，可以获取这个类型。

比如：Promise<ExampleType>，请你返回 ExampleType 类型

解答

type MyAwaited<T extends Promise<unknown>> = T extends Promise<infer X> ? (X extends Promise<unknown> ? MyAwaited<X> : X) : never

type MyAwaited<T extends Promise<unknown>> = T extends Promise<infer X> ? (X extends Promise<unknown> ? MyAwaited<X> : X) : never

268.if

限制C的类型为boolean，然后判断C extends true 还是false，返回正确的值

type If<C extends boolean, T, F> = C extends true ? T : F

type If<C extends boolean, T, F> = C extends true ? T : F

type If<C extends boolean, T, F> = C extends true ? T : F
// 结果：'a'
type result1 = If<true, "a", "b">
// 结果：'b'
type result2 = If<false, "a", "b">

type If<C extends boolean, T, F> = C extends true ? T : F
// 结果：'a'
type result1 = If<true, "a", "b">
// 结果：'b'
type result2 = If<false, "a", "b">

3057.Includes

Implement the JavaScript Array.includes function in the type system.A type takes the two arguments.The output should be a boolean true or false
在类型系统中实现JavaScript的Array.includes 函数，一个包含两个参数的类型，返回的类型是true 或 false。

示例

type isPillarMen = Includes<['Kars', 'Esidisi', 'Wamuu', 'Santana'], 'Dio'> // expected to be `false`

type isPillarMen = Includes<['Kars', 'Esidisi', 'Wamuu', 'Santana'], 'Dio'> // expected to be `false`

测试用例

import type { Equal, Expect } from '@type-challenges/utils'

type cases = [
  Expect<Equal<Includes<['Kars', 'Esidisi', 'Wamuu', 'Santana'], 'Kars'>, true>>,
  Expect<Equal<Includes<['Kars', 'Esidisi', 'Wamuu', 'Santana'], 'Dio'>, false>>,
  Expect<Equal<Includes<[1, 2, 3, 5, 6, 7], 7>, true>>,
  Expect<Equal<Includes<[1, 2, 3, 5, 6, 7], 4>, false>>,
  Expect<Equal<Includes<[1, 2, 3], 2>, true>>,
  Expect<Equal<Includes<[1, 2, 3], 1>, true>>,
  Expect<Equal<Includes<[{}], { a: 'A' }>, false>>,
  Expect<Equal<Includes<[boolean, 2, 3, 5, 6, 7], false>, false>>,
  Expect<Equal<Includes<[true, 2, 3, 5, 6, 7], boolean>, false>>,
  Expect<Equal<Includes<[false, 2, 3, 5, 6, 7], false>, true>>,
  Expect<Equal<Includes<[{ a: 'A' }], { readonly a: 'A' }>, false>>,
  Expect<Equal<Includes<[{ readonly a: 'A' }], { a: 'A' }>, false>>,
  Expect<Equal<Includes<[1], 1 | 2>, false>>,
  Expect<Equal<Includes<[1 | 2], 1>, false>>,
  Expect<Equal<Includes<[null], undefined>, false>>,
  Expect<Equal<Includes<[undefined], null>, false>>,
]

import type { Equal, Expect } from '@type-challenges/utils'

type cases = [
  Expect<Equal<Includes<['Kars', 'Esidisi', 'Wamuu', 'Santana'], 'Kars'>, true>>,
  Expect<Equal<Includes<['Kars', 'Esidisi', 'Wamuu', 'Santana'], 'Dio'>, false>>,
  Expect<Equal<Includes<[1, 2, 3, 5, 6, 7], 7>, true>>,
  Expect<Equal<Includes<[1, 2, 3, 5, 6, 7], 4>, false>>,
  Expect<Equal<Includes<[1, 2, 3], 2>, true>>,
  Expect<Equal<Includes<[1, 2, 3], 1>, true>>,
  Expect<Equal<Includes<[{}], { a: 'A' }>, false>>,
  Expect<Equal<Includes<[boolean, 2, 3, 5, 6, 7], false>, false>>,
  Expect<Equal<Includes<[true, 2, 3, 5, 6, 7], boolean>, false>>,
  Expect<Equal<Includes<[false, 2, 3, 5, 6, 7], false>, true>>,
  Expect<Equal<Includes<[{ a: 'A' }], { readonly a: 'A' }>, false>>,
  Expect<Equal<Includes<[{ readonly a: 'A' }], { a: 'A' }>, false>>,
  Expect<Equal<Includes<[1], 1 | 2>, false>>,
  Expect<Equal<Includes<[1 | 2], 1>, false>>,
  Expect<Equal<Includes<[null], undefined>, false>>,
  Expect<Equal<Includes<[undefined], null>, false>>,
]

解答

type Includes<T extends readonly any[], U> = T extends [infer First, ...infer Rest]
  ? Equal<First, U> extends true
    ? true
    : Includes<Rest, U>
  : false

type Includes<T extends readonly any[], U> = T extends [infer First, ...infer Rest]
  ? Equal<First, U> extends true
    ? true
    : Includes<Rest, U>
  : false

总结

T extends [infer First, ...infer Rest]中infer First和infer Rest分别占位数组的第一个和数组的剩余元素，

Equal<First, U> extends true表示数组第一个元素和第二个传入的参数相同的情况下，返回true,否则使用递归方式来继续执行，从而遍历数组的元素

3057.Push

Implement the type version of Array.push
实现类型版本的 Array.push

示例

type Result = Push<[1, 2], '3'> // [1, 2, '3']

type Result = Push<[1, 2], '3'> // [1, 2, '3']

测试用例

import type { Equal, Expect } from '@type-challenges/utils'

type cases = [
  Expect<Equal<Push<[], 1>, [1]>>,
  Expect<Equal<Push<[1, 2], '3'>, [1, 2, '3']>>,
  Expect<Equal<Push<['1', 2, '3'], boolean>, ['1', 2, '3', boolean]>>
]

import type { Equal, Expect } from '@type-challenges/utils'

type cases = [
  Expect<Equal<Push<[], 1>, [1]>>,
  Expect<Equal<Push<[1, 2], '3'>, [1, 2, '3']>>,
  Expect<Equal<Push<['1', 2, '3'], boolean>, ['1', 2, '3', boolean]>>
]

解答

type Push<T extends any[], U> = [...T, U]

type Push<T extends any[], U> = [...T, U]

总结

T extends any[]表示限制传入的第一个类型是一个任意的数组类型

3060.Unshift

实现类型版本的 Array.unshift

示例

type Result = Unshift<[1, 2], 0> // [0, 1, 2]

type Result = Unshift<[1, 2], 0> // [0, 1, 2]

测试用例

import type { Equal, Expect } from "@type-challenges/utils"

type cases = [
  Expect<Equal<Unshift<[], 1>, [1]>>,
  Expect<Equal<Unshift<[1, 2], 0>, [0, 1, 2]>>,
  Expect<Equal<Unshift<["1", 2, "3"], boolean>, [boolean, "1", 2, "3"]>>
]

import type { Equal, Expect } from "@type-challenges/utils"

type cases = [
  Expect<Equal<Unshift<[], 1>, [1]>>,
  Expect<Equal<Unshift<[1, 2], 0>, [0, 1, 2]>>,
  Expect<Equal<Unshift<["1", 2, "3"], boolean>, [boolean, "1", 2, "3"]>>
]

解答

type Unshift<T extends any[], U> = [U, ...T]

type Unshift<T extends any[], U> = [U, ...T]

3312.Parameters

Implement the built-in Parameters generic without using it
实现内置的Parameters泛型，而不是使用它

测试用例

import type { Equal, Expect } from "@type-challenges/utils"

const foo = (arg1: string, arg2: number): void => {}
const bar = (arg1: boolean, arg2: { a: "A" }): void => {}
const baz = (): void => {}

type cases = [
  Expect<Equal<MyParameters<typeof foo>, [string, number]>>,
  Expect<Equal<MyParameters<typeof bar>, [boolean, { a: "A" }]>>,
  Expect<Equal<MyParameters<typeof baz>, []>>
]

import type { Equal, Expect } from "@type-challenges/utils"

const foo = (arg1: string, arg2: number): void => {}
const bar = (arg1: boolean, arg2: { a: "A" }): void => {}
const baz = (): void => {}

type cases = [
  Expect<Equal<MyParameters<typeof foo>, [string, number]>>,
  Expect<Equal<MyParameters<typeof bar>, [boolean, { a: "A" }]>>,
  Expect<Equal<MyParameters<typeof baz>, []>>
]

解答

type MyParameters<T extends (...args: any) => any> = T extends (...args: infer R) => any
  ? [...R]
  : any

type MyParameters<T extends (...args: any) => any> = T extends (...args: infer R) => any
  ? [...R]
  : any

总结

(...args: any) => any是一个整体，表示一个参数任意，返回值任意的函数类型

T extends (...args: any) => any表示限制传入的类型必须是一个函数类型

T extends (...args: infer R) => any其中的infer R用来占位，这里的R表示的就是参数的类型，之后就可以通过...展开运算符来展开R，从而返回参数的数组类型

type-challenges #

warm-up #

13.helloworld #

解答 #

easy #

4.pick #

解答 #

7.Readonly #

解答 #

11.Tuple to Object #

解答 #

14.First of Array #

解答 #

18.Length of Tuple #

解答 #

43.Exclude #

解答 #

189.Awaited #

解答 #

268.if #

3057.Includes #

示例 #

测试用例 #

解答 #

总结 #

3057.Push #

示例 #

测试用例 #

解答 #

总结 #

3060.Unshift #

示例 #

测试用例 #

解答 #

3312.Parameters #

测试用例 #

解答 #

总结 #

type-challenges

warm-up

13.helloworld

解答

easy

4.pick

解答

7.Readonly

解答

11.Tuple to Object

解答

14.First of Array

解答

18.Length of Tuple

解答

43.Exclude

解答

189.Awaited

解答

268.if

3057.Includes

示例

测试用例

解答

总结

3057.Push

示例

测试用例

解答

总结

3060.Unshift

示例

测试用例

解答

3312.Parameters

测试用例

解答

总结