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ts基础知识温习
https://juejin.cn/post/684490...
ts中的拜访修饰符
- public，任何中央
- private，只能在类的外部拜访
- protected，能在类的外部拜访和子类中拜访
- readonly，属性设置为只读
const和readonly的区别
- const用于变量，readonly用于属性
- const在运行时查看，readonly在编译时查看
应用const变量保留的数组，能够应用push，pop等办法。然而如果应用
ReadonlyArray<number>申明的数组不能应用push，pop等办法。枚举和常量枚举（const枚举）的区别
- 枚举会被编译时会编译成一个对象，能够被当作对象应用
- const枚举会在ts编译期间被删除，防止额定的性能开销
// 一般枚举enum Witcher { Ciri = 'Queen', Geralt = 'Geralt of Rivia'}function getGeraltMessage(arg: {[key: string]: string}): string { return arg.Geralt}getGeraltMessage(Witcher) // Geralt of Rivia// const枚举const enum Witcher { Ciri = 'Queen', Geralt = 'Geralt of Rivia'}const witchers: Witcher[] = [Witcher.Ciri, Witcher.Geralt]// 编译后// const witchers = ['Queen', 'Geralt of Rivia'ts中interface能够给Function/Array/Class做申明吗？
// 函数类型interface SearchFunc { (source: string, subString: string): boolean;}let mySearch: SearchFunc;mySearch = function(source: string, subString: string) { let result = source.search(subString); return result > -1;}// Arrayinterface StringArray { [index: number]: string;}let myArray: StringArray;myArray = ["Bob", "Fred"];// Class, constructor存在于类的动态局部，所以不会查看interface ClockInterface { currentTime: Date; setTime(d: Date);}class Clock implements ClockInterface { currentTime: Date; setTime(d: Date) { this.currentTime = d; } constructor(h: number, m: number) { }}ts中的this和js中的this有什么差别？
不理解
ts中如何枚举联结类型的key?
type Name = { name: string }type Age = { age: number }type Union = Name | Agetype UnionKey<P> = P extends infer P ? keyof P : nevertype T = UnionKey<Union>ts中 ?.、??、!.、_、** 等符号的含意？
- ?. 可选链
- ?? ?? 相似与短路或，??防止了一些意外状况0，NaN以及"",false被视为false值。只有undefind,null被视为false值。
- !. 在变量名后增加!，能够断言排除undefined和null类型
- _ , 申明该函数将被传递一个参数，但您并不关怀它
- ** 求幂
- !:，待会调配这个变量，ts不要放心
// ??let x = foo ?? bar();// 等价于let x = foo !== null && foo !== undefined ? foo : bar();// !.let a: string | null | undefineda.length // errora!.length // ok什么是抗变、双变、协变和逆变？
- Covariant 协变，TS对象兼容性是协变，父类 <= 子类，是能够的。子类 <= 父类，谬误。
- Contravariant 逆变，禁用
strictFunctionTypes编译，函数参数类型是逆变的，父类 <= 子类，是谬误。子类 <= 父类，是能够的。 Bivariant 双向协变，函数参数的类型默认是双向协变的。父类 <= 子类，是能够的。子类 <= 父类，是能够的。
ts中同名的interface或者同名的interface和class能够合并吗？
- interface会合并
- class不能够合并
如何使ts我的项目引入并辨认编译为js的npm库包？
npm install @types/xxxx本人增加形容文件
ts如何主动生成库包的申明文件？
能够配置tsconfig.json文件中的declaration和outDir
- declaration: true, 将会主动生成申明文件
- outDir: '', 指定目录
什么是泛型
泛型用来来创立可重用的组件，一个组件能够反对多种类型的数据。这样用户就能够以本人的数据类型来应用组件。简略的说，“泛型就是把类型当成参数”。
-?，-readonly 是什么含意
用于删除修饰符
type A = { a: string; b: number;}type B = { [K in keyof A]?: A[K]}type C = { [K in keyof B]-?: B[K]}type D = { readonly [K in keyof A]: A[K]}type E = { -readonly [K in keyof A]: A[K]}TS是基于构造类型兼容
typescript的类型兼容是基于构造的，不是基于名义的。上面的代码在ts中是齐全能够的，但在java等基于名义的语言则会抛错。
interface Named { name: string }class Person { name: string}let p: Named// okp = new Person()const断言
const断言，typescript会为变量增加一个本身的字面量类型
- 对象字面量的属性，取得readonly的属性，成为只读属性
- 数组字面量成为readonly tuple只读元组
- 字面量类型不能被扩大（比方从hello类型到string类型）
// type '"hello"'let x = "hello" as const// type 'readonly [10, 20]'let y = [10, 20] as const// type '{ readonly text: "hello" }'let z = { text: "hello" } as consttype 和 interface 的区别
- 类型别名能够为任何类型引入名称。例如根本类型，联结类型等
- 类型别名不反对继承
- 类型别名不会创立一个真正的名字
- 类型别名无奈被实现(implements)，而接口能够被派生类实现
- 类型别名重名时编译器会抛出谬误，接口重名时会产生合并
implements 与 extends 的区别
- extends, 子类会继承父类的所有属性和办法。
implements，应用implements关键字的类将须要实现须要实现的类的所有属性和办法。
枚举和 object 的区别
- 枚举能够通过枚举的名称，获取枚举的值。也能够通过枚举的值获取枚举的名称。
- object只能通过key获取value
- 数字枚举在不指定初始值的状况下，枚举值会从0开始递增。
- 尽管在运行时，枚举是一个实在存在的对象。然而应用keyof时的行为却和一般对象不统一。必须应用keyof typeof才能够获取枚举所有属性名。
never, void 的区别
- never，never示意永远不存在的类型。比方一个函数总是抛出谬误，而没有返回值。或者一个函数外部有死循环，永远不会有返回值。函数的返回值就是never类型。
- void, 没有显示的返回值的函数返回值为void类型。如果一个变量为void类型，只能赋予undefined或者null。
unknown, any的区别
unknown类型和any类型相似。与any类型不同的是。unknown类型能够承受任意类型赋值，然而unknown类型赋值给其余类型前，必须被断言
如何在 window 扩大类型
declare global { interface Window { myCustomFn: () => void; }}简单的类型推导题目
implement UnionToIntersection<T>
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%8Bimplement ToNumber<T>
type A = ToNumber<'1'> // 1type B = ToNumber<'40'> // 40type C = ToNumber<'0'> // 0// 实现ToNumbertype ToNumber<T extends string, R extends any[] = []> = T extends `${R['length']}` ? R['length'] : ToNumber<T, [1, ...R]>;implement Add<A, B>
type A = Add<1, 2> // 3type B = Add<0, 0> // 0// 实现ADDtype NumberToArray<T, R extends any[]> = T extends R['length'] ? R : NumberToArray<T, [1, ...R]>type Add<T, R> = [...NumberToArray<T, []>, ...NumberToArray<R, []>]['length']implement SmallerThan<A, B>
type A = SmallerThan<0, 1> // truetype B = SmallerThan<1, 0> // falsetype C = SmallerThan<10, 9> // false// 实现SmallerThantype 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]>;implement LargerThan<A, B>
type A = LargerThan<0, 1> // falsetype B = LargerThan<1, 0> // truetype C = LargerThan<10, 9> // true// 实现LargerThantype 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]>;implement IsAny<T>
type A = IsAny<string> // falsetype B = IsAny<any> // truetype C = IsAny<unknown> // falsetype D = IsAny<never> // false// 实现IsAnytype IsAny<T> = true extends (T extends never ? true : false) ? false extends (T extends never ? true : false) ? true : false : false;// 更简略的实现type IsAny<T> = 0 extends (T & 1) ? true : false;implement Filter<T, A>
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Filtertype 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;implement TupleToString<T>
type A = TupleToString<['a']> // 'a'type B = TupleToString<['B', 'F', 'E']> // 'BFE'type C = TupleToString<[]> // ''// 实现TupleToStringtype TupleToString<T extends any[], S extends string = '', A extends any[] = []> = A['length'] extends T['length'] ? S : TupleToString<T, `${S}${T[A['length']]}`, [1, ...A]>implement RepeatString<T, C>
type A = RepeatString<'a', 3> // 'aaa'type B = RepeatString<'a', 0> // ''// 实现RepeatStringtype RepeatString<T extends string, C extends number, S extends string = '', A extends any[] = []> = A['length'] extends C ? S : RepeatString<T, C, `${T}${S}`, [1, ...A]>implement Push<T, I>
type A = Push<[1,2,3], 4> // [1,2,3,4]type B = Push<[1], 2> // [1, 2]type C = Push<[], string> // [string]// 实现Pushtype Push<T extends any[], I> = T extends [...infer P] ? [...P, I] : [I]implement Flat<T>
type A = Flat<[1,2,3]> // [1,2,3]type B = Flat<[1,[2,3], [4,[5,[6]]]]> // [1,2,3,4,5,6]type C = Flat<[]> // []// 实现Flattype Flat<T extends any[]> = T extends [infer P, ...infer Q] ? P extends any[] ? [...Flat<P>, ...Flat<Q>] : [P, ...Flat<Q>] : [];implement Shift<T>
type A = Shift<[1,2,3]> // [2,3]type B = Shift<[1]> // []type C = Shift<[]> // []// 实现Shifttype Shift<T extends any[]> = T extends [infer P, ...infer Q] ? [...Q] : [];implement Repeat<T, C>
type A = Repeat<number, 3> // [number, number, number]type B = Repeat<string, 2> // [string, string]type C = Repeat<1, 1> // [1, 1]type D = Repeat<0, 0> // []// 实现Repeattype Repeat<T, C, R extends any[] = []> = R['length'] extends C ? R : Repeat<T, C, [...R, T]>implement ReverseTuple<T>
type A = ReverseTuple<[string, number, boolean]> // [boolean, number, string]type B = ReverseTuple<[1,2,3]> // [3,2,1]type C = ReverseTuple<[]> // []// 实现ReverseTupletype ReverseTuple<T extends any[], A extends any[] = []> = T extends [...infer Q, infer P] ? A['length'] extends T['length'] ? A : ReverseTuple<Q, [...A, P]> : A;implement UnwrapPromise<T>
type A = UnwrapPromise<Promise<string>> // stringtype B = UnwrapPromise<Promise<null>> // nulltype C = UnwrapPromise<null> // Error// 实现UnwrapPromisetype UnwrapPromise<T> = T extends Promise<infer P> ? P : Error;implement LengthOfString<T>
type A = LengthOfString<'BFE.dev'> // 7type B = LengthOfString<''> // 0// 实现LengthOfStringtype LengthOfString<T extends string, A extends any[] = []> = T extends `${infer P}${infer Q}` ? LengthOfString<Q, [1, ...A]> : A['length']implement StringToTuple<T>
type A = StringToTuple<'BFE.dev'> // ['B', 'F', 'E', '.', 'd', 'e','v']type B = StringToTuple<''> // []// 实现type StringToTuple<T extends string, A extends any[] = []> = T extends `${infer K}${infer P}` ? StringToTuple<P, [...A, K]> : A;implement LengthOfTuple<T>
type A = LengthOfTuple<['B', 'F', 'E']> // 3type B = LengthOfTuple<[]> // 0// 实现type LengthOfTuple<T extends any[], R extends any[] = []> = R['length'] extends T['length'] ? R['length'] : LengthOfTuple<T, [...R, 1]>implement LastItem<T>
type A = LastItem<[string, number, boolean]> // booleantype B = LastItem<['B', 'F', 'E']> // 'E'type C = LastItem<[]> // never// 实现LastItemtype LastItem<T> = T extends [...infer P, infer Q] ? Q : never;implement FirstItem<T>
type A = FirstItem<[string, number, boolean]> // stringtype B = FirstItem<['B', 'F', 'E']> // 'B'// 实现FirstItemtype FirstItem<T> = T extends [infer P, ...infer Q] ? P : never;implement FirstChar<T>
type A = FirstChar<'BFE'> // 'B'type B = FirstChar<'dev'> // 'd'type C = FirstChar<''> // never// 实现FirstChartype FirstChar<T> = T extends `${infer P}${infer Q}` ? P : never;implement Pick<T, K>
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]}implement Readonly<T>
type Foo = { a: string}const a:Foo = { a: 'BFE.dev',}a.a = 'bigfrontend.dev'// OKconst b:MyReadonly<Foo> = { a: 'BFE.dev'}b.a = 'bigfrontend.dev'// Error// 实现MyReadonlytype MyReadonly<T> = { readonly [K in keyof T]: T[K]}implement Record<K, V>
type Key = 'a' | 'b' | 'c'const a: Record<Key, string> = { a: 'BFE.dev', b: 'BFE.dev', c: 'BFE.dev'}a.a = 'bigfrontend.dev' // OKa.b = 123 // Errora.d = 'BFE.dev' // Errortype Foo = MyRecord<{a: string}, string> // Error// 实现MyRecordtype MyRecord<K extends number | string | symbol, V> = { [Key in K]: V}️ implement Exclude
type Foo = 'a' | 'b' | 'c'type A = MyExclude<Foo, 'a'> // 'b' | 'c'type B = MyExclude<Foo, 'c'> // 'a' | 'btype 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;️ implement Extract<T, U>
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 : neverimplement Omit<T, K>
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MyOmittype 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>>implement NonNullable<T>
type Foo = 'a' | 'b' | null | undefinedtype A = MyNonNullable<Foo> // 'a' | 'b'// 实现NonNullabletype MyNonNullable<T> = T extends null | undefined ? never : T;implement Parameters<T>
type Foo = (a: string, b: number, c: boolean) => stringtype A = MyParameters<Foo> // [a:string, b: number, c:boolean]type B = A[0] // stringtype C = MyParameters<{a: string}> // Error// 实现MyParameters<T>type MyParameters<T extends (...params: any[]) => any> = T extends (...params: [...infer P]) => any ? P : neverimplement ConstructorParameters<T>
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 : neverimplement ReturnType<T>
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;implement InstanceType<T>
class Foo {}type A = MyInstanceType<typeof Foo> // Footype 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;implement ThisParameterType<T>
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;implement TupleToUnion<T>
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;// 其余答复type TupleToUnion<T extends any[]> = T[number]implement Partial<T>
type Foo = { a: string b: number c: boolean}// below are all validconst 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]}Required<T>
// all properties are optionaltype Foo = { a?: string b?: number c?: boolean}const a: MyRequired<Foo> = {}// Errorconst b: MyRequired<Foo> = { a: 'BFE.dev'}// Errorconst c: MyRequired<Foo> = { b: 123}// Errorconst d: MyRequired<Foo> = { b: 123, c: true}// Errorconst e: MyRequired<Foo> = { a: 'BFE.dev', b: 123, c: true}// valid// 实现MyRequired<T>type MyRequired<T> = { [K in keyof T]-?: T[K]}implement LastChar<T>
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}${infer Q}` ? LastChar<Q, [...A, P]> : A extends [...infer L, infer R] ? R : never;implement IsNever<T>
// https://stackoverflow.com/questions/53984650/typescript-never-type-inconsistently-matched-in-conditional-type// https://www.typescriptlang.org/docs/handbook/advanced-types.html#vtype A = IsNever<never> // truetype B = IsNever<string> // falsetype C = IsNever<undefined> // false// 实现IsNever<T>type IsNever<T> = [T] extends [never] ? true : false;implement KeysToUnion<T>
type A = KeyToUnion<{ a: string; b: number; c: symbol;}>// 'a' | 'b' | 'c'// 实现KeyToUniontype KeyToUnion<T> = { [K in keyof T]: K;}[keyof T]implement ValuesToUnion<T>
type A = ValuesToUnion<{ a: string; b: number; c: symbol;}>// string | number | symbol// ValuesToUniontype ValuesToUnion<T> = T[keyof T]FindIndex<T, E>
https://bigfrontend.dev/zh/ty...
type IsAny<T> = 0 extends (T & 1) ? true : false;type IsNever<T> = [T] extends [never] ? true : false;type TwoAny<A, B> = IsAny<A> extends IsAny<B> ? IsAny<A> : false;type TwoNever<A, B> = IsNever<A> extends IsNever<B> ? IsNever<A> : false;type SingleAny<A, B> = IsAny<A> extends true ? true : IsAny<B>type SingleNever<A, B> = IsNever<A> extends true ? true : IsNever<B>type FindIndex<T extends any[], E, A extends any[] = []> = T extends [infer P, ...infer Q] ? TwoAny<P, E> extends true ? A['length'] : TwoNever<P, E> extends true ? A['length'] : SingleAny<P, E> extends true ? FindIndex<Q, E, [1, ...A]> : SingleNever<P, E> extends true ? FindIndex<Q, E, [1, ...A]> : P extends E ? A['length'] : FindIndex<Q, E, [1, ...A]> : neverimplement Trim<T>
type A = Trim<' BFE.dev'> // 'BFE'type B = Trim<' BFE. dev '> // 'BFE. dev'type C = Trim<' BFE . dev '> // 'BFE . dev'type StringToTuple<T extends string, A extends any[] = []> = T extends `${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> : '' : '';还有更多 UnionToTuple, IntersectionToUnion ?