I think I was comparing typeof checks to more than just ```'undefined'```, for example, to ```'function'```. That gets 60 on the current repository, and 850 across Gaia. I still think that when you're attempting to check that a variable's type meets (or does not meet) your expectations, it's nice to always do the same thing. ```typeof``` works in every situation, and you write it the same way every time. 

I think that's a nice property (kind of like how we don't *really* need to use semicolons everywhere, but choose to in order to reduce the mental overhead and trickiness of the language). However, I don't think it's worth arguing over here, so I've committed the ```opts.id !== undefined``` style.