One way to get a comma-free JSON-like format is to write the document in hjson, which is a superset of JSON.
var config = HJSON.parse(fs.fileReadSync('config.hjson'))
Another more obscure, and more powerful serialization format that does away with commas (commas are treated as whitespace!), has a date type, and much more is Rich Hickey's (of Clojure fame) EDN. https://github.com/edn-format/edn
{:a 1, "foo" :bar, [1 2 3] four}