How should I name a function which shows or hides an element?
Naming

I think togglePassenger is not the only naming problem in your code. 

A function parameter should not be a single letter except in a very limited number of cases. But I don't think that this is not one of them; a reader does not automatically understand what i actually does.

I would also rename nbPassengers, because it is unclear what nb means.

What I think your function does is show the first n passengers, and hide the rest. If that is the case, I would not use toggle, because as you said, there really is no toggling going on. You could go with something like updateVisibility to avoid this confusion, although it's a bit unconcrete. Whatever name you do choose, I would add a comment to the function explaining what it does.

Misc


I would use curly brackets even for one line statements to avoid future bugs
your spacing is sometimes inconsistent (eg spacing around variable in function calls)