Join
题目
Github: Join
实现数组类型的 Array.join 版本，Join<T, U> 接受一个数组 T，字符串或数字 U，并返回用 U 拼接后的数组 T。
type Res = Join<['a', 'p', 'p', 'l', 'e'], '-'> // expected to be 'a-p-p-l-e'
type Res1 = Join<['Hello', 'World'], ' '> // expected to be 'Hello World'
type Res2 = Join<['2', '2', '2'], 1> // expected to be '21212'
type Res3 = Join<['o'], 'u'> // expected to be 'o'解题思路
略。
答案
type Join<T extends any[], U extends string | number = ','> =
T extends [infer F, ...infer O]
? O['length'] extends 0
? `${F & string}`
: `${F & string}${U}${Join<O, U>}`
: ''验证
type cases = [
Expect<Equal<Join<['a', 'p', 'p', 'l', 'e'], '-'>, 'a-p-p-l-e'>>,
Expect<Equal<Join<['Hello', 'World'], ' '>, 'Hello World'>>,
Expect<Equal<Join<['2', '2', '2'], 1>, '21212'>>,
Expect<Equal<Join<['o'], 'u'>, 'o'>>,
Expect<Equal<Join<[], 'u'>, ''>>,
Expect<Equal<Join<['1', '1', '1']>, '1,1,1'>>,
]