Typescript实现

🤔 implement UnionToIntersection

type A = UnionToIntersection<{a: string} | {b: string} | {c: string}> 
// {a: string} & {b: string} & {c: string}

// 实现UnionToIntersection<T>
type UnionToIntersection<U> = 
  (U extends any ? (k: U) => void : never) extends ((k: infer I) => void) ? I : never
// https://stackoverflow.com/questions/50374908/transform-union-type-to-intersection-type
// https://jkchao.github.io/typescript-book-chinese/tips/infer.html#%E4%B8%80%E4%BA%9B%E7%94%A8%E4%BE%8B
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😊 implement ToNumber

type A = ToNumber<'1'> // 1
type B = ToNumber<'40'> // 40
type C = ToNumber<'0'> // 0

// 实现ToNumber
type ToNumber<T extends string, R extends any[] = []> =
    T extends `${R['length']}` ? R['length'] : ToNumber<T, [1, ...R]>;
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😊 implement Add

type A = Add<1, 2> // 3
type B = Add<0, 0> // 0

// 实现ADD
type NumberToArray<T, R extends any[]> = T extends R['length'] ? R : NumberToArray<T, [1, ...R]>
type Add<T, R> = [...NumberToArray<T, []>, ...NumberToArray<R, []>]['length']
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😊 implement SmallerThan

type A = SmallerThan<0, 1> // true
type B = SmallerThan<1, 0> // false
type C = SmallerThan<10, 9> // false

// 实现SmallerThan
type SmallerThan<N extends number, M extends number, L extends any[] = [], R extends any[] = []> = 
    N extends L['length'] ? 
        M extends R['length'] ? false : true
        :
        M extends R['length'] ? false : SmallerThan<N, M, [1, ...L], [1, ...R]>;
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😊 implement LargerThan

type A = LargerThan<0, 1> // false
type B = LargerThan<1, 0> // true
type C = LargerThan<10, 9> // true

// 实现LargerThan
type LargerThan<N extends number, M extends number, L extends any[] = [], R extends any[] = []> =
    N extends L['length'] ?
        false : M extends R['length'] ?
            true : LargerThan<N, M, [1, ...L], [1, ...R]>;
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😊 implement IsAny

type A = IsAny<string> // false
type B = IsAny<any> // true
type C = IsAny<unknown> // false
type D = IsAny<never> // false

// 实现IsAny
type IsAny<T> = true extends (T extends never ? true : false) ?
                  false extends (T extends never ? true : false) ?
                    true
                    :
                    false
                  :
                  false;

// 更简单的实现
type IsAny<T> = 0 extends (T & 1) ? true : false;
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😊 implement Filter

type A = Filter<[1,'BFE', 2, true, 'dev'], number> // [1, 2]
type B = Filter<[1,'BFE', 2, true, 'dev'], string> // ['BFE', 'dev']
type C = Filter<[1,'BFE', 2, any, 'dev'], string> // ['BFE', any, 'dev']

// 实现Filter
type Filter<T extends any[], A, N extends any[] = []> =
    T extends [infer P, ...infer Q] ?
        0 extends (P & 1) ? Filter<Q, A, [...N, P]> : 
        P extends A ? Filter<Q, A, [...N, P]> : Filter<Q, A, N>
        : N;
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😊 implement TupleToString

type A = TupleToString<['a']> // 'a'
type B = TupleToString<['B', 'F', 'E']> // 'BFE'
type C = TupleToString<[]> // ''

// 实现TupleToString
type TupleToString<T extends any[], S extends string = '', A extends any[] = []> =
    A['length'] extends T['length'] ? S : TupleToString<T, `${S}${T[A['length']]}`, [1, ...A]>
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😊 implement RepeatString

type A = RepeatString<'a', 3> // 'aaa'
type B = RepeatString<'a', 0> // ''

// 实现RepeatString
type RepeatString<T extends string, C extends number, S extends string = '', A extends any[] = []> =
    A['length'] extends C ? S : RepeatString<T, C, `${T}${S}`, [1, ...A]>
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😊 implement Push

type A = Push<[1,2,3], 4> // [1,2,3,4]
type B = Push<[1], 2> // [1, 2]
type C = Push<[], string> // [string]

// 实现Push
type Push<T extends any[], I> = T extends [...infer P] ? [...P, I] : [I]
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😊 implement Flat

type A = Flat<[1,2,3]> // [1,2,3]
type B = Flat<[1,[2,3], [4,[5,[6]]]]> // [1,2,3,4,5,6]
type C = Flat<[]> // []

// 实现Flat
type Flat<T extends any[]> =
    T extends [infer P, ...infer Q] ?
        P extends any[] ? [...Flat<P>, ...Flat<Q>] : [P, ...Flat<Q>]
        : [];
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😊 implement Shift

type A = Shift<[1,2,3]> // [2,3]
type B = Shift<[1]> // []
type C = Shift<[]> // []

// 实现Shift
type Shift<T extends any[]> = T extends [infer P, ...infer Q] ? [...Q] : [];
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😊 implement Repeat

type A = Repeat<number, 3> // [number, number, number]
type B = Repeat<string, 2> // [string, string]
type C = Repeat<1, 1> // [1, 1]
type D = Repeat<0, 0> // []

// 实现Repeat
type Repeat<T, C, R extends any[] = []> = 
    R['length'] extends C ? R : Repeat<T, C, [...R, T]>
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😊 implement ReverseTuple

type A = ReverseTuple<[string, number, boolean]> // [boolean, number, string]
type B = ReverseTuple<[1,2,3]> // [3,2,1]
type C = ReverseTuple<[]> // []

// 实现ReverseTuple
type ReverseTuple<T extends any[], A extends any[] = []> =
    T extends [...infer Q, infer P] ? 
        A['length'] extends T['length'] ? A : ReverseTuple<Q, [...A, P]>
        : A;
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😊 implement UnwrapPromise

type A = UnwrapPromise<Promise<string>> // string
type B = UnwrapPromise<Promise<null>> // null
type C = UnwrapPromise<null> // Error

// 实现UnwrapPromise
type UnwrapPromise<T> = T extends Promise<infer P> ? P : Error;
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😊 implement LengthOfString

type A = LengthOfString<'BFE.dev'> // 7
type B = LengthOfString<''> // 0

// 实现LengthOfString
type LengthOfString<T extends string, A extends any[] = []> =
    T extends `${infer P}${infer Q}` ? LengthOfString<Q, [1, ...A]> : A['length']
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😊 implement StringToTuple

type A = StringToTuple<'BFE.dev'> // ['B', 'F', 'E', '.', 'd', 'e','v']
type B = StringToTuple<''> // []

// 实现
type StringToTuple<T extends string, A extends any[] = []> =
    T extends `${infer K}${infer P}` ? StringToTuple<P, [...A, K]> : A;
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😊 implement LengthOfTuple

type A = LengthOfTuple<['B', 'F', 'E']> // 3
type B = LengthOfTuple<[]> // 0

// 实现
type LengthOfTuple<T extends any[], R extends any[] = []> =
    R['length'] extends T['length'] ? R['length'] : LengthOfTuple<T, [...R, 1]>
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😊 implement LastItem

type A = LastItem<[string, number, boolean]> // boolean
type B = LastItem<['B', 'F', 'E']> // 'E'
type C = LastItem<[]> // never

// 实现LastItem
type LastItem<T> = T extends [...infer P, infer Q] ? Q : never;
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😊 implement FirstItem

type A = FirstItem<[string, number, boolean]> // string
type B = FirstItem<['B', 'F', 'E']> // 'B'

// 实现FirstItem
type FirstItem<T> = T extends [infer P, ...infer Q] ? P : never;
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😊 implement FirstChar

type A = FirstChar<'BFE'> // 'B'
type B = FirstChar<'dev'> // 'd'
type C = FirstChar<''> // never

// 实现FirstChar
type FirstChar<T> = T extends `${infer P}${infer Q}` ? P : never;
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😊 implement Pick

type Foo = {
  a: string
  b: number
  c: boolean
}

type A = MyPick<Foo, 'a' | 'b'> // {a: string, b: number}
type B = MyPick<Foo, 'c'> // {c: boolean}
type C = MyPick<Foo, 'd'> // Error

// 实现MyPick<T, K>
type MyPick<T, K extends keyof T> = {
    [Key in K]: T[Key]
}
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😊 implement Readonly

type Foo = {
  a: string
}

const a:Foo = {
  a: 'BFE.dev',
}
a.a = 'bigfrontend.dev'
// OK

const b:MyReadonly<Foo> = {
  a: 'BFE.dev'
}
b.a = 'bigfrontend.dev'
// Error

// 实现MyReadonly
type MyReadonly<T> = {
    readonly [K in keyof T]: T[K]
}
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😊 implement Record

type Key = 'a' | 'b' | 'c'

const a: Record<Key, string> = {
  a: 'BFE.dev',
  b: 'BFE.dev',
  c: 'BFE.dev'
}
a.a = 'bigfrontend.dev' // OK
a.b = 123 // Error
a.d = 'BFE.dev' // Error

type Foo = MyRecord<{a: string}, string> // Error

// 实现MyRecord
type MyRecord<K extends number | string | symbol, V> = {
    [Key in K]: V
}
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😊 implement Exclude

type Foo = 'a' | 'b' | 'c'

type A = MyExclude<Foo, 'a'> // 'b' | 'c'
type B = MyExclude<Foo, 'c'> // 'a' | 'b
type C = MyExclude<Foo, 'c' | 'd'>  // 'a' | 'b'
type D = MyExclude<Foo, 'a' | 'b' | 'c'>  // never

// 实现 MyExclude<T, K>
type MyExclude<T, K> = T extends K ? never : T;
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😊 implement Extract

type Foo = 'a' | 'b' | 'c'

type A = MyExtract<Foo, 'a'> // 'a'
type B = MyExtract<Foo, 'a' | 'b'> // 'a' | 'b'
type C = MyExtract<Foo, 'b' | 'c' | 'd' | 'e'>  // 'b' | 'c'
type D = MyExtract<Foo, never>  // never

// 实现MyExtract<T, U>
type MyExtract<T, U> = T extends U ? T : never
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😊 implement Omit

type Foo = {
  a: string
  b: number
  c: boolean
}

type A = MyOmit<Foo, 'a' | 'b'> // {c: boolean}
type B = MyOmit<Foo, 'c'> // {a: string, b: number}
type C = MyOmit<Foo, 'c' | 'd'> // {a: string, b: number}

// 实现MyOmit
type MyOmit<T, K extends number | string | symbol> = {
    [Key in Exclude<keyof T, K>]: T[Key]
}

type MyOmit<T, K extends number | string | symbol> = Pick<T, Exclude<keyof T, K>>
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😊 implement NonNullable

type Foo = 'a' | 'b' | null | undefined

type A = MyNonNullable<Foo> // 'a' | 'b'

// 实现NonNullable
type MyNonNullable<T> = T extends null | undefined ? never : T;
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😊 implement Parameters

type Foo = (a: string, b: number, c: boolean) => string

type A = MyParameters<Foo> // [a:string, b: number, c:boolean]
type B = A[0] // string
type C = MyParameters<{a: string}> // Error

// 实现MyParameters<T>
type MyParameters<T extends (...params: any[]) => any> =
    T extends (...params: [...infer P]) => any ? P : never
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😊 implement ConstructorParameters

class Foo {
  constructor (a: string, b: number, c: boolean) {}
}

type C = MyConstructorParameters<typeof Foo> 
// [a: string, b: number, c: boolean]

// 实现MyConstructorParameters<T>
type MyConstructorParameters<T extends new (...params: any[]) => any> =
    T extends new (...params: [...infer P]) => any ? P : never
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😊 implement ReturnType

type Foo = () => {a: string}

type A = MyReturnType<Foo> // {a: string}

// 实现MyReturnType<T>
type MyReturnType<T extends (...params: any[]) => any> =
    T extends (...params: any[]) => infer P ? P : never;
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😊 implement InstanceType

class Foo {}
type A = MyInstanceType<typeof Foo> // Foo
type B = MyInstanceType<() => string> // Error

// 实现MyInstanceType<T>
type MyInstanceType<T extends new (...params: any[]) => any> =
    T extends new (...params: any[]) => infer P ? P : never;
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😊 implement ThisParameterType

function Foo(this: {a: string}) {}
function Bar() {}

type A = MyThisParameterType<typeof Foo> // {a: string}
type B = MyThisParameterType<typeof Bar> // unknown

// 实现MyThisParameterType<T>
type MyThisParameterType<T extends (this: any, ...params: any[]) => any> =
    T extends (this: infer P, ...params: any[]) => any ? P : unknown;
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😊 implement TupleToUnion

type Foo = [string, number, boolean]

type Bar = TupleToUnion<Foo> // string | number | boolean

// 实现TupleToUnion<T>
type TupleToUnion<T extends any[], R = T[0]> =
    T extends [infer P, ...infer Q] ? TupleToUnion<Q, R | P> : R;

// 其他回答
type TupleToUnion<T extends any[]> = T[number]
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😊 implement Partial

type Foo = {
  a: string
  b: number
  c: boolean
}

// below are all valid

const a: MyPartial<Foo> = {}

const b: MyPartial<Foo> = {
  a: 'BFE.dev'
}

const c: MyPartial<Foo> = {
  b: 123
}

const d: MyPartial<Foo> = {
  b: 123,
  c: true
}

const e: MyPartial<Foo> = {
  a: 'BFE.dev',
  b: 123,
  c: true
}

// 实现MyPartial<T>
type MyPartial<T> = {
    [K in keyof T]?: T[K]
}
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😊 Required

// all properties are optional
type Foo = {
  a?: string
  b?: number
  c?: boolean
}


const a: MyRequired<Foo> = {}
// Error

const b: MyRequired<Foo> = {
  a: 'BFE.dev'
}
// Error

const c: MyRequired<Foo> = {
  b: 123
}
// Error

const d: MyRequired<Foo> = {
  b: 123,
  c: true
}
// Error

const e: MyRequired<Foo> = {
  a: 'BFE.dev',
  b: 123,
  c: true
}
// valid

// 实现MyRequired<T>
type MyRequired<T> = {
    [K in keyof T]-?: T[K]
}
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😊 implement LastChar

type A = LastChar<'BFE'> // 'E'
type B = LastChar<'dev'> // 'v'
type C = LastChar<''> // never

// 实现FirstChar<T>
type LastChar<T extends string, A extends string[] = []> =
    T extends `${infer P}${infer Q}` ?  LastChar<Q, [...A, P]> :
        A extends [...infer L, infer R] ? R : never
;
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😊 implement IsNever

// https://stackoverflow.com/questions/53984650/typescript-never-type-inconsistently-matched-in-conditional-type
// https://www.typescriptlang.org/docs/handbook/advanced-types.html#v
type A = IsNever<never> // true
type B = IsNever<string> // false
type C = IsNever<undefined> // false

// 实现IsNever<T>
type IsNever<T> = [T] extends [never] ? true : false;
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😊 implement KeysToUnion

type A = KeyToUnion<{
  a: string;
  b: number;
  c: symbol;
}>
// 'a' | 'b' | 'c'

// 实现KeyToUnion
type KeyToUnion<T> = {
  [K in keyof T]: K;
}[keyof T]
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😊 implement ValuesToUnion

type A = ValuesToUnion<{
  a: string;
  b: number;
  c: symbol;
}>
// string | number | symbol

// ValuesToUnion
type ValuesToUnion<T> = T[keyof T]
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FindIndex

bigfrontend.dev/zh/typescri…

type IsAny<T> = 0 extends (T & 1) ? true : false;
type IsNever<T> = [T] extends [never] ? true : false;

type TwoAny<A, B> = IsAny<A> extends IsAny<B> ? IsAny<A> : false;
type TwoNever<A, B> = IsNever<A> extends IsNever<B> ? IsNever<A> : false;

type SingleAny<A, B> = IsAny<A> extends true ? true : IsAny<B>
type SingleNever<A, B> = IsNever<A> extends true ? true : IsNever<B>


type FindIndex<T extends any[], E, A extends any[] = []> =
    T extends [infer P, ...infer Q] ?
        TwoAny<P, E> extends true ? 
            A['length']
            :
            TwoNever<P, E> extends true ?
                A['length']
                :
                SingleAny<P, E> extends true ?
                    FindIndex<Q, E, [1, ...A]>
                    :
                    SingleNever<P, E> extends true ?
                        FindIndex<Q, E, [1, ...A]>
                        :
                        P extends E ? A['length'] : FindIndex<Q, E, [1, ...A]>
        : 
        never
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implement Trim

type A = Trim<'    BFE.dev'> // 'BFE'
type B = Trim<' BFE. dev  '> // 'BFE. dev'
type C = Trim<'  BFE .   dev  '> // 'BFE .   dev'

type StringToTuple<T extends string, A extends any[] = []> =
    T extends `${infer K}${infer P}` ? StringToTuple<P, [...A, K]> : A;

type TupleToString<T extends any[], S extends string = '', A extends any[] = []> =
    A['length'] extends T['length'] ? S : TupleToString<T, `${S}${T[A['length']]}`, [1, ...A]>

type Trim<T extends string, A extends any[] = StringToTuple<T>> =
    A extends [infer P, ...infer Q] ?
        P extends ' ' ?
            Trim<T, Q>
            :
            A extends [...infer M, infer N] ? 
                N extends ' ' ?
                    Trim<T, M>
                    :
                    TupleToString<A>
                :
                ''
        :
        '';

作者：dyhtps
链接：https://juejin.cn/post/6988763249982308382
来源：稀土掘金
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