Xin's Blog

Appearance

TS Challenge ​

Easy ​

  1. 实现 Pick

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

  2. 实现 Readonly

    typescript
    type MyReadOnly<T> = {
	readonly [P in keyof T]: T[P]
}

  3. 实现 Tuple 转 对象

    typescript
    type TupleToObject<T extends readonly (string|number)[]> {
  [P in T[number]]: P
}

  4. 第一个元素

    typescript
    type First<T extends any[]> = T extends [] ? never : T[0]

  5. 实现 Exclude

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

/* _____________ 测试用例 _____________ */
import type { Equal, Expect } from '@type-challenges/utils'

type cases = [
  Expect<Equal<MyExclude<'a' | 'b' | 'c', 'a'>, 'b' | 'c'>>,
  Expect<Equal<MyExclude<'a' | 'b' | 'c', 'a' | 'b'>, 'c'>>,
  Expect<Equal<MyExclude<string | number | (() => void), Function>, string | number>>,
]

  6. 实现 if

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

  7. 实现Concat

    typescript
    type Concat<T extends readonly any[], U extends readonly any[]> = [...T, ...U]

    实现Equals

    typescript
    type Equals<X, Y> =
    (<T>() => T extends X ? 1 : 2) extends
    (<T>() => T extends Y ? 1 : 2) ? true : false;

  8. 实现Includes

    typescript
    type Includes<Value extends any[], Item> =
	Equals<Value[0], Item> extends true
		? true
		: Value extends [Value[0], ...infer rest]
			? Includes<rest, Item>
			: false;

  9. 实现push

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

/* _____________ 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]>>,
]

  10. 实现unshift

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

/* _____________ 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']>>,
]

  11. 实现Parameters

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

/* _____________ 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>, []>>,
]

Medium ​

  1. 获取函数返回类型

    typescript
    type MyReturnType<T extends Function> = T extends (...args: any) => infer R ? R : never

/* _____________ 测试用例 _____________ */
import type { Equal, Expect } from '@type-challenges/utils'

type cases = [
  Expect<Equal<string, MyReturnType<() => string>>>,
  Expect<Equal<123, MyReturnType<() => 123>>>,
  Expect<Equal<ComplexObject, MyReturnType<() => ComplexObject>>>,
  Expect<Equal<Promise<boolean>, MyReturnType<() => Promise<boolean>>>>,
  Expect<Equal<() => 'foo', MyReturnType<() => () => 'foo'>>>,
  Expect<Equal<1 | 2, MyReturnType<typeof fn>>>,
  Expect<Equal<1 | 2, MyReturnType<typeof fn1>>>,
]

type ComplexObject = {
  a: [12, 'foo']
  bar: 'hello'
  prev(): number
}

const fn = (v: boolean) => v ? 1 : 2
const fn1 = (v: boolean, w: any) => v ? 1 : 2

  2. 实现Omit

    typescript
    
type MyOmit<T, K extends keyof T> = {
  [P in keyof T as P extends K ? never : P]:T[P]
}

/* _____________ 测试用例 _____________ */
import type { Equal, Expect } from '@type-challenges/utils'

type cases = [
  Expect<Equal<Expected1, MyOmit<Todo, 'description'>>>,
  Expect<Equal<Expected2, MyOmit<Todo, 'description' | 'completed'>>>,
]

// @ts-expect-error
type error = MyOmit<Todo, 'description' | 'invalid'>

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

interface Expected1 {
  title: string
  completed: boolean
}

interface Expected2 {
  title: string
}

  3. 对象部分属性只读

    typescript
    type MyReadonly2<T, K extends keyof T = keyof T> = {
  [p in keyof T as p extends K? never: p]: T[p]
} & {
  readonly [p in K]: T[p]
}

/* _____________ 测试用例 _____________ */
import type { Alike, Expect } from '@type-challenges/utils'

type cases = [
  Expect<Alike<MyReadonly2<Todo1>, Readonly<Todo1>>>,
  Expect<Alike<MyReadonly2<Todo1, 'title' | 'description'>, Expected>>,
  Expect<Alike<MyReadonly2<Todo2, 'title' | 'description'>, Expected>>,
  Expect<Alike<MyReadonly2<Todo2, 'description' >, Expected>>,
]

// @ts-expect-error
type error = MyReadonly2<Todo1, 'title' | 'invalid'>

interface Todo1 {
  title: string
  description?: string
  completed: boolean
}

interface Todo2 {
  readonly title: string
  description?: string
  completed: boolean
}

interface Expected {
  readonly title: string
  readonly description?: string
  completed: boolean
}

  4. 实现元祖转集合

    typescript
    type TupleToUnion<T extends any[]> = T[number]

/* _____________ 测试用例 _____________ */
import type { Equal, Expect } from '@type-challenges/utils'

type cases = [
  Expect<Equal<TupleToUnion<[123, '456', true]>, 123 | '456' | true>>,
  Expect<Equal<TupleToUnion<[123]>, 123>>,
]

  5. 最后一个元素

    typescript
    type Last<T extends any[]> = [never, ...T][T['length']]

/* _____________ 测试用例 _____________ */
import type { Equal, Expect } from '@type-challenges/utils'

type cases = [
  Expect<Equal<Last<[2]>, 2>>,
  Expect<Equal<Last<[3, 2, 1]>, 1>>,
  Expect<Equal<Last<[() => 123, { a: string }]>, { a: string }>>,
]

  6. 实现Pop

    typescript
    type Pop<T extends any[]> = T extends [...infer U, any] ? U : never

/* _____________ 测试用例 _____________ */
import type { Equal, Expect } from '@type-challenges/utils'

type cases = [
  Expect<Equal<Pop<[3, 2, 1]>, [3, 2]>>,
  Expect<Equal<Pop<['a', 'b', 'c', 'd']>, ['a', 'b', 'c']>>,
  Expect<Equal<Pop<[]>, []>>,
]

    一些举一反三

    typescript
    type Push<T extends unknown[], U> = [...T, U]
type Shift<T extends unknown[]> = T extends [unknown, ...infer U] ? U : never
type Unshift<T extends unknown[], U> = [U, ...T]

  7. 实现Promise.all

    typescript
    declare function PromiseAll<T extends any[]>(values: readonly [...T]): Promise<{
  [key in keyof T]: Awaited<T[key]>
}>

/* _____________ 测试用例 _____________ */
import type { Equal, Expect } from '@type-challenges/utils'

const promiseAllTest1 = PromiseAll([1, 2, 3] as const)
const promiseAllTest2 = PromiseAll([1, 2, Promise.resolve(3)] as const)
const promiseAllTest3 = PromiseAll([1, 2, Promise.resolve(3)])
const promiseAllTest4 = PromiseAll<Array<number | Promise<number>>>([1, 2, 3])

type cases = [
  Expect<Equal<typeof promiseAllTest1, Promise<[1, 2, 3]>>>,
  Expect<Equal<typeof promiseAllTest2, Promise<[1, 2, number]>>>,
  Expect<Equal<typeof promiseAllTest3, Promise<[number, number, number]>>>,
  Expect<Equal<typeof promiseAllTest4, Promise<number[]>>>,
]

  8. 实现TrimLeft

    typescript
    /* _____________ 你的代码 _____________ */

type Space = ' ' | '\n' | '\t'
type TrimLeft<S extends string> = S extends `${Space}${infer R}` ? TrimLeft<R> : S

/* _____________ 测试用例 _____________ */
import type { Equal, Expect } from '@type-challenges/utils'

type cases = [
  Expect<Equal<TrimLeft<'str'>, 'str'>>,
  Expect<Equal<TrimLeft<' str'>, 'str'>>,
  Expect<Equal<TrimLeft<'     str'>, 'str'>>,
  Expect<Equal<TrimLeft<'     str     '>, 'str     '>>,
  Expect<Equal<TrimLeft<'   \n\t foo bar '>, 'foo bar '>>,
  Expect<Equal<TrimLeft<''>, ''>>,
  Expect<Equal<TrimLeft<' \n\t'>, ''>>,
]

  9. 实现TrimRight

    typescript
    type WhiteSpace = ' ' | '\n' | '\t'
type Trim<S> = S extends `${WhiteSpace}${infer T}`|`${infer T}${WhiteSpace}`? Trim<T>:S

/* _____________ 测试用例 _____________ */
import type { Equal, Expect } from '@type-challenges/utils'

type cases = [
  Expect<Equal<Trim<'str'>, 'str'>>,
  Expect<Equal<Trim<' str'>, 'str'>>,
  Expect<Equal<Trim<'     str'>, 'str'>>,
  Expect<Equal<Trim<'str   '>, 'str'>>,
  Expect<Equal<Trim<'     str     '>, 'str'>>,
  Expect<Equal<Trim<'   \n\t foo bar \t'>, 'foo bar'>>,
  Expect<Equal<Trim<''>, ''>>,
  Expect<Equal<Trim<' \n\t '>, ''>>,
]

  10. Capitalize

    typescript
    type MyCapitalize<S extends string> = S extends `${infer F}${infer tail}` ? `${Uppercase<F>}${tail}` : S

/* _____________ 测试用例 _____________ */
import type { Equal, Expect } from '@type-challenges/utils'

type cases = [
  Expect<Equal<MyCapitalize<'foobar'>, 'Foobar'>>,
  Expect<Equal<MyCapitalize<'FOOBAR'>, 'FOOBAR'>>,
  Expect<Equal<MyCapitalize<'foo bar'>, 'Foo bar'>>,
  Expect<Equal<MyCapitalize<''>, ''>>,
  Expect<Equal<MyCapitalize<'a'>, 'A'>>,
  Expect<Equal<MyCapitalize<'b'>, 'B'>>,
  Expect<Equal<MyCapitalize<'c'>, 'C'>>,
  Expect<Equal<MyCapitalize<'d'>, 'D'>>,
  Expect<Equal<MyCapitalize<'e'>, 'E'>>,
  Expect<Equal<MyCapitalize<'f'>, 'F'>>,
  Expect<Equal<MyCapitalize<'g'>, 'G'>>,
  Expect<Equal<MyCapitalize<'h'>, 'H'>>,
  Expect<Equal<MyCapitalize<'i'>, 'I'>>,
  Expect<Equal<MyCapitalize<'j'>, 'J'>>,
  Expect<Equal<MyCapitalize<'k'>, 'K'>>,
  Expect<Equal<MyCapitalize<'l'>, 'L'>>,
  Expect<Equal<MyCapitalize<'m'>, 'M'>>,
  Expect<Equal<MyCapitalize<'n'>, 'N'>>,
  Expect<Equal<MyCapitalize<'o'>, 'O'>>,
  Expect<Equal<MyCapitalize<'p'>, 'P'>>,
  Expect<Equal<MyCapitalize<'q'>, 'Q'>>,
  Expect<Equal<MyCapitalize<'r'>, 'R'>>,
  Expect<Equal<MyCapitalize<'s'>, 'S'>>,
  Expect<Equal<MyCapitalize<'t'>, 'T'>>,
  Expect<Equal<MyCapitalize<'u'>, 'U'>>,
  Expect<Equal<MyCapitalize<'v'>, 'V'>>,
  Expect<Equal<MyCapitalize<'w'>, 'W'>>,
  Expect<Equal<MyCapitalize<'x'>, 'X'>>,
  Expect<Equal<MyCapitalize<'y'>, 'Y'>>,
  Expect<Equal<MyCapitalize<'z'>, 'Z'>>,
]

  11. Replace

    typescript
    type Replace<S extends string, From extends string, To extends string> = 
From extends ''
? S
: S extends `${infer V}${From}${infer R}`
  ? `${V}${To}${R}`
  : S

/* _____________ 测试用例 _____________ */
import type { Equal, Expect } from '@type-challenges/utils'

type cases = [
  Expect<Equal<Replace<'foobar', 'bar', 'foo'>, 'foofoo'>>,
  Expect<Equal<Replace<'foobarbar', 'bar', 'foo'>, 'foofoobar'>>,
  Expect<Equal<Replace<'foobarbar', '', 'foo'>, 'foobarbar'>>,
  Expect<Equal<Replace<'foobarbar', 'bar', ''>, 'foobar'>>,
  Expect<Equal<Replace<'foobarbar', 'bra', 'foo'>, 'foobarbar'>>,
  Expect<Equal<Replace<'', '', ''>, ''>>,
]

  12. ReplaceAll

 ```typescript
 type ReplaceAll<S extends string, From extends string, To extends string> = From extends '' ? S : S extends `${infer R}${From}${infer Q}` ? `${ReplaceAll<R, From, To>}${To}${ReplaceAll<Q, From, To>}` : S;11
 
 /* _____________ 测试用例 _____________ */
 import type { Equal, Expect } from '@type-challenges/utils'
 
 type cases = [
   Expect<Equal<ReplaceAll<'foobar', 'bar', 'foo'>, 'foofoo'>>,
   Expect<Equal<ReplaceAll<'foobar', 'bag', 'foo'>, 'foobar'>>,
   Expect<Equal<ReplaceAll<'foobarbar', 'bar', 'foo'>, 'foofoofoo'>>,
   Expect<Equal<ReplaceAll<'t y p e s', ' ', ''>, 'types'>>,
   Expect<Equal<ReplaceAll<'foobarbar', '', 'foo'>, 'foobarbar'>>,
   Expect<Equal<ReplaceAll<'barfoo', 'bar', 'foo'>, 'foofoo'>>,
   Expect<Equal<ReplaceAll<'foobarfoobar', 'ob', 'b'>, 'fobarfobar'>>,
   Expect<Equal<ReplaceAll<'foboorfoboar', 'bo', 'b'>, 'foborfobar'>>,
   Expect<Equal<ReplaceAll<'', '', ''>, ''>>,
 ]
 ```

  1. IsNever

    typescript
    type IsNever<T> = Equal<T, never>

/* _____________ Test Cases _____________ */
import type { Equal, Expect } from '@type-challenges/utils'

type cases = [
  Expect<Equal<IsNever<never>, true>>,
  Expect<Equal<IsNever<never | string>, false>>,
  Expect<Equal<IsNever<''>, false>>,
  Expect<Equal<IsNever<undefined>, false>>,
  Expect<Equal<IsNever<null>, false>>,
  Expect<Equal<IsNever<[]>, false>>,
  Expect<Equal<IsNever<{}>, false>>,
]

  2. IsAny

    typescript
    type IsAny<T> = Equal<T, any>
/* _____________ Test Cases _____________ */
import type { Equal, Expect } from '@type-challenges/utils'

type cases = [
  Expect<Equal<IsAny<any>, true>>,

  Expect<Equal<IsAny<undefined>, false>>,
  Expect<Equal<IsAny<unknown>, false>>,
  Expect<Equal<IsAny<never>, false>>,
  E

  3. Absolute

    核心解法是，是将 T 转换为字符串，然后检查字符串前面是否有 -。 如果有，则返回 - 之后的字符串，否则返回已转换为字符串的 T。

    typescript
    
type Absolute<T extends number | string | bigint> = `${T}` extends `-${infer U}` ? U : `${T}`

/* _____________ 测试用例 _____________ */
import type { Equal, Expect } from '@type-challenges/utils'

type cases = [
  Expect<Equal<Absolute<0>, '0'>>,
  Expect<Equal<Absolute<-0>, '0'>>,
  Expect<Equal<Absolute<10>, '10'>>,
  Expect<Equal<Absolute<-5>, '5'>>,
  Expect<Equal<Absolute<'0'>, '0'>>,
  Expect<Equal<Absolute<'-0'>, '0'>>,
  Expect<Equal<Absolute<'10'>, '10'>>,
  Expect<Equal<Absolute<'-5'>, '5'>>,
  Expect<Equal<Absolute<-1_000_000n>, '1000000'>>,
  Expect<Equal<Absolute<9_999n>, '9999'>>,
]

  4. startsWith

    typescript
    type StartsWith<T extends string, U extends string> = T extends `${U}${string}` ? true : false

/* _____________ 测试用例 _____________ */
import type { Equal, Expect } from '@type-challenges/utils'

type cases = [
  Expect<Equal<StartsWith<'abc', 'ac'>, false>>,
  Expect<Equal<StartsWith<'abc', 'ab'>, true>>,
  Expect<Equal<StartsWith<'abc', 'abc'>, true>>,
  Expect<Equal<StartsWith<'abc', 'abcd'>, false>>,
  Expect<Equal<StartsWith<'abc', ''>, true>>,
  Expect<Equal<StartsWith<'abc', ' '>, false>>,
  Expect<Equal<StartsWith<'', ''>, true>>,
]

  5. EndsWith

    typescript
    type EndsWith<T extends string, U extends string> = T extends `${string}${U}` ? true : false

/* _____________ 测试用例 _____________ */
import type { Equal, Expect } from '@type-challenges/utils'

type cases = [
  Expect<Equal<EndsWith<'abc', 'bc'>, true>>,
  Expect<Equal<EndsWith<'abc', 'abc'>, true>>,
  Expect<Equal<EndsWith<'abc', 'd'>, false>>,
  Expect<Equal<EndsWith<'abc', 'ac'>, false>>,
  Expect<Equal<EndsWith<'abc', ''>, true>>,
  Expect<Equal<EndsWith<'abc', ' '>, false>>,
]

    1. PartialByKeys

      ts
      /* _____________ 你的代码 _____________ */

type PartialByKeys<T extends {}, U = keyof T> = 
  Omit<Partial<Pick<T, U & keyof T>> & Omit<T, U & keyof T>, never>;

/* _____________ 测试用例 _____________ */
import type { Equal, Expect } from '@type-challenges/utils'

interface User {
  name: string
  age: number
  address: string
}

interface UserPartialName {
  name?: string
  age: number
  address: string
}

interface UserPartialNameAndAge {
  name?: string
  age?: number
  address: string
}

type cases = [
  Expect<Equal<PartialByKeys<User, 'name'>, UserPartialName>>,
  Expect<Equal<PartialByKeys<User, 'name' | 'age'>, UserPartialNameAndAge>>,
  Expect<Equal<PartialByKeys<User>, Partial<User>>>,
  // @ts-expect-error
  Expect<Equal<PartialByKeys<User, 'name' | 'unknown'>, UserPartialName>>,
]

Made with ❤️ by Xin

Copyright © 2019-present Xin