I don't use JS, but in PHP you can add a comma after the last item, which I usually do, and therefore I don't have the problems that you encountered. Of course, I believe that people should do what works best for them, and if you find comma first easier to work with, then great!

Edit: And in response to your first comment about your IDE not supporting this: Is it not trivial to identify a syntax error in JS when you attempt to run it? Surely the intepreter (browser?) will notify you of the line that the syntax error occured on?