技术

TypeScript 挑战（五）- 获取元素长度

学习记录 - 获取元素长度 - 对于给定的元组，您需要创建一个通用的Length，选择元组的长度

题目简介

对于给定的元组，您需要创建一个通用的Length，选择元组的长度

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

测试用例

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

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

type cases = [
  Expect<Equal<Length<typeof tesla>, 4>>,
  Expect<Equal<Length<typeof spaceX>, 5>>,
]

答案

type Length<T extends any> = T extends ArrayLike<any> ? T["length"] : never