[Typescript] 41. Medium - IsUnion
typescript 41 Medium
2023-09-14 09:00:45 时间
Implement a type IsUnion
, which takes an input type T
and returns whether T
resolves to a union type.
For example:
type case1 = IsUnion<string> // false
type case2 = IsUnion<string|number> // true
type case3 = IsUnion<[string|number]> // false
Not fully understand how the solution works.
/* _____________ Your Code Here _____________ */
type IsUnion<T, C = T> = [T] extends [never]
? false
: T extends C
? [C] extends [T]
? false
: true
: never;
// [T]: [void | "" | null | undefined]
// [C]: [void] | [""] | [null] | [undefined]
type x= IsUnion<undefined | null | void | ''>
/* _____________ Test Cases _____________ */
import type { Equal, Expect } from '@type-challenges/utils'
type cases = [
Expect<Equal<IsUnion<string>, false>>,
Expect<Equal<IsUnion<string | number>, true>>,
Expect<Equal<IsUnion<'a' | 'b' | 'c' | 'd'>, true>>,
Expect<Equal<IsUnion<undefined | null | void | ''>, true>>,
Expect<Equal<IsUnion<{ a: string } | { a: number }>, true>>,
Expect<Equal<IsUnion<{ a: string | number }>, false>>,
Expect<Equal<IsUnion<[string | number]>, false>>,
// Cases where T resolves to a non-union type.
Expect<Equal<IsUnion<string | never>, false>>,
Expect<Equal<IsUnion<string | unknown>, false>>,
Expect<Equal<IsUnion<string | any>, false>>,
Expect<Equal<IsUnion<string | 'a'>, false>>,
Expect<Equal<IsUnion<never>, false>>,
]
相关文章
- [Typescript] 59. Medium - InorderTraversal
- [Typescript] Tips: Create your own 'objectKeys' function using generics and the 'keyof' operator
- [Typescript] 26. Medium - Trim
- [Typescript] 13. Easy - Unshift
- [TypeScript] infer
- [TypeScript] Overload a Function with TypeScript’s Overload Signatures
- [Angular] Short Imports with TypeScript Path Mapping
- [Typescript 4.9] Auto-Accessors in Classes
- [Typescript] 44. Medium - Drop char
- [Typescript] 25. Medium - Trim Left
- [Vuex] Split Vuex Store into Modules using TypeScript
- [Typescript] Make TypeScript Class Usage Safer with Strict Property Initialization
- typescript入门简明教程
- TypeScript 全面介绍