189 - Awaited (🎥 Video Explanation and Solution) #21536
Description
189 - Awaited
Awaited is a nice early look at how recursive types look in TypeScript. Hopefully, by the end of this challenge you are starting to see how powerful TypeScript's type system is. It feels magical if you only see the tests, but if you see a solution it should make more sense.
🎥 Video Explanation
🔢 Code
import type { Equal, Expect } from "./test-utils";
type A1 = MyAwaited<Promise<string>>
type B1 = string;
type C1 = Expect<Equal<A1, B1>>;
type A2 = MyAwaited<Promise<{ field: number }>>
type B2 = { field: number };
type C2 = Expect<Equal<A2, B2>>;
type A3 = MyAwaited<Promise<Promise<string | number>>>
type B3 = string | number;
type C3 = Expect<Equal<A3, B3>>;
type A4 = MyAwaited<
Promise<Promise<Promise<string | boolean>>>
>
type B4 = string | boolean;
type C4 = Expect<Equal<A4, B4>>;
// @ts-expect-error(2344)
type E1 = MyAwaited<number>;
// ============= Your Code Here =============
type MyAwaited<T extends Promise<unknown>> =
T extends Promise<infer U>
? U extends Promise<unknown>
? MyAwaited<U>
: U
: T
;
type MyAwaited<T> =
T extends PromiseLike<infer P>
? P
: never
;➕ More Solutions
For more video solutions to other challenges: see the umbrella list! #21338