Absolute

约 252 字小于 1 分钟

2026-02-11

题目

实现一个接收string,number或bigInt类型参数的Absolute类型,返回一个正数字符串。

例如

type Test = -100
type Result = Absolute<Test> // expected to be "100"

解题思路

利用模板字符串会把数字转成十进制字符串的原理，匹配第一个字符是否为 -，取其数字部分即可。

答案

type Absolute<T extends number | string | bigint> = `${T}` extends `${infer F}${infer R}`
  ? (F extends '-' ? R : `${F}${R}`)
  : ''

验证

type cases
 = [
  Expect
<Equal
<Absolute
<0>, '0'>>,
  Expect
<Equal
<Absolute
<-0>, '0'>>,
  Expect
<Equal
<Absolute
<10>, '10'>>,
  Expect
<Equal
<Absolute
<-5>, '5'>>,
  Expect
<Equal
<Absolute
<'0'>, '0'>>,
  Expect
<Equal
<Absolute
<'-0'>, '0'>>,
  Expect
<Equal
<Absolute
<'10'>, '10'>>,
  Expect
<Equal
<Absolute
<'-5'>, '5'>>,
  Expect
<Equal
<Absolute
<-1_000_000n>, '1000000'>>,
  Expect
<Equal
<Absolute
<9_999n>, '9999'>>,
]

参考

模板字面量类型 Template Literal Types
条件类型 Conditional Types
条件类型中的类型推断 Type Inference in Conditional Types

贡献者

Cuber-Wei