Exactly. Leaving off the return type annotation is just asking for trouble, and this example proves it. And the actual type of the const won't be `string | num

Exactly. Leaving off the return type annotation is just asking for trouble, and this example proves it. And the actual type of the const won't be `string | number` -- it will be `any`. MaulingMonkey[1] has the right idea, though. [1] https://news.ycombinator.com/item?id=12192240 https://news.ycombinator.com/item?id=12192240