What I don't want is this `if` each time we run this function. I want a as-linearized-as-possible code. Explicit is better than implicit. I don't want magic functions that can take everything (but, hey, not everything, a Number won't work) as argument.

Moreover, with a `filterByString` function, the fact that it implies type was a goal. Also, defining it just above the main `filterBy` function makes that it isn't really defined in 2 places, rather in _this_ place.

However, I don't see any current code that makes use of an object (filter) argument. So I'd be perfectly happy with removing the if-block completely as it was before.