type UnwrapPromise<T> = T extends PromiseLike<infer U> ? U : T;

// Example Usage:
type StringPromise = Promise<string>;
type NumberPromise = Promise<number[]>;
type NonPromise = boolean;

type ResolvedString = UnwrapPromise<StringPromise>; // string
type ResolvedNumberArray = UnwrapPromise<NumberPromise>; // number[]
type ResolvedNonPromise = UnwrapPromise<NonPromise>; // boolean

async function fetchData(): Promise<{ data: string }> {
  return { data: 'some data' };
}

// Using with ReturnType for async functions:
type FetchDataReturnType = ReturnType<typeof fetchData>; // Promise<{ data: string }>
type FetchedDataType = UnwrapPromise<FetchDataReturnType>; // { data: string }