type-challenges-sollutions.md

Solutions

Warm-up

Easy

4. Pick

type MyPick<T, K extends keyof T> = {
  [U in K]: T[U];
}

10. Readonly

type MyReadonly<T> = {
  readonly [U in keyof T]: T[U];
}

14. First of Array

type First<T extends any[]> = T['length'] extends 0 ? never : T[0]; 

Perhaps you don't know you can get length of an array type.

18. Lengh of Tuple

type Length<T extends readonly unknown[]> = T['length'];

43. Exclude

type MyExclude<T, U> = T extends U ? never : T;

Actually, it runs for each sub type of a union type.

189. Awaited

type Awaited<T extends Promise<any>> = T extends Promise<infer U> ? U : never;

533. Contact

type Concat<T extends unknown[], U extends unknown[]> = [...T, ...U];

Medium

Hard