Length of String 2

题目来源(type-challenges)

问题 #

type case1 = LengthOfString<''> // 0
type case2 = LengthOfString<'1'> // 1
type case3 = LengthOfString<'12'> // 2
type case4 = LengthOfString<'123'> // 3
type case5 = LengthOfString<'1234'> // 4
type case6 = LengthOfString<'12345'> // 5
type case7 = LengthOfString<'123456'> // 6
type case8 = LengthOfString<'1234567'> // 7
type case9 = LengthOfString<'12345678'> // 8
type case10 = LengthOfString<'123456789'> // 9

解答 #

type LengthOfString<S extends string, Res extends unknown[] = []> =
  S extends `${infer _}${infer Tail}`
  ? LengthOfString<Tail, [...Res, unknown]>
  : Res['length']

拆分 #

• 拆分字后用数组统计长度
• 然后不能拆分返回长度