Yeah, you don't technically have to, but if you write production code, it is a good idea to leave the structure there for a couple of reasons. This example is trivial, but you may want to have a default parameter in place, in which case you need the parenthesis (ie: (n=10) => ...), also the parenthesis clearly marks where there function param is, and for anything but one-liners like this, highlighting the name of that parameter argument is helpful, and worth the time to write the parenthesis.