How to make the Awaited type pass the error test case?

[mrdulin]

It's so weird. I can't think of any way.

type MyAwaited<T> = T extends PromiseLike<infer V> ? MyAwaited<V> : T

// @ts-expect-error
type error = MyAwaited<number>

Got error:

Unused '@ts-expect-error' directive.

So I think I didn't pass the error test case.

TS Playground

[ChrisKulesza]

@mrdulin
You must restrict your generic type of MyAwaited to PromiseLike. Like so. But then you still haven't reached your destination. Since you still have to take care of nested PromiseLikes.

type MyAwaited<T extends PromiseLike<unknown>> = T extends PromiseLike<infer V> ? MyAwaited<V> : T

[mrdulin]

Thanks for your reply. But TSC throws an error for your answer:

Type 'V' does not satisfy the constraint 'PromiseLike'.(2344)

[jazelly]

Type 'V' does not satisfy the constraint 'PromiseLike'.(2344)

This error simply means V does not satisfy the T extends PromiseLike<unknown> condition. To suppress it, You can simply add check after infer, e..g infer V extends PromiseLike<any>, or defer it to next if else

[ChrisKulesza]

I know. That's why I gave you the recursion hint. If this is not enough for you, then you can also work with the solutions of the other users here.