type PromisableFields<ObjectType> = {
  [Key in keyof ObjectType]: Promisable<ObjectType[Key]>;
};

interface Foo {
  bar: number;
  baz: string;
}

type UnresolvedFoo = PromisableFields<Foo>;
/*
This would yield the following type:
{
  bar: Promisable<number>;
  baz: Promisable<string>;
}
*/

export async function resolveFields<ObjectType>(
  promisableObject: PromisableFields<ObjectType>
): Promise<ObjectType> {
  const partial = {} as Partial<ObjectType>;
  for (const [key, promisableValue] of Object.entries(promisableObject)) {
    partial[key] = await promisableValue;
  }
  return partial as ObjectType;
}