Coming from a lisp I often wish other languages had `cond` so I don't have to nest if statements. This looks like a poor man's cond.

So yes, I do find this more readable. It makes it clear that only one branch will get executed.

This would be equally clear if the author had just used a sequence of if statements with a 'return' in each one. (Note that Javascript's case has fallthrough, so you can't immediately conclude that only one branch of a case will be executed.)

You don't have to nest if-statements and I would say nested-if is wrong. You simply use else-if. It's a flat structure just like cond.

you mean two if statements. The last case is a default return.