Trim

In this medium-level challenge, you'll implement Trim<T> which takes an exact string type and returns a new string with the whitespace from both ends removed.

[object Object]

// Video Solution: https://youtube.com/watch?v=fALHOdurTDM

/* _____________ Your Code Here _____________ */

type Trim<S extends string> = any

/* _____________ Test Cases _____________ */
import type { Equal, Expect } from '../helpers'

type cases = [
  Expect<Equal<Trim<'str'>, 'str'>>,
  Expect<Equal<Trim<' str'>, 'str'>>,
  Expect<Equal<Trim<'     str'>, 'str'>>,
  Expect<Equal<Trim<'str   '>, 'str'>>,
  Expect<Equal<Trim<'     str     '>, 'str'>>,
  Expect<Equal<Trim<'   \n\t foo bar \t'>, 'foo bar'>>,
  Expect<Equal<Trim<''>, ''>>,
  Expect<Equal<Trim<' \n\t '>, ''>>,
]

Detailed Explanation

type Whitespace = ' ' | '\n' | '\t'
 
type Trim<S extends string> = S extends `${Whitespace}${infer After}`
  ? Trim<After>
  : S extends `${infer Before}${Whitespace}`
    ? Trim<Before>
    : S

How it works:

• First, we define a type Whitespace that represents all whitespace characters
• Next, we constrain the type S to be a string with extends string
• S extends ${Whitespace}${infer After} matches the string type and captures the rest of the string into After
• ? Trim<After> recursively calls Trim with the rest of the string
• : S returns the string if it doesn't start or end with a whitespace character (base case)

This challenge helps you understand TypeScript's template literal types and how to apply this concept in real-world scenarios.