Trailing commas simplify adding and removing items to objects and arrays, since only the lines you are modifying must be touched. Another argument in favor of trailing commas is that it improves the clarity of diffs when an item is added or removed from an object or array
In writing PR #13, I added a line to an array and had to edit two lines instead of 1 because of the eslint rule which is set to never instead of always. Since you’re transpiling anyway, I don’t see the benefit to disallowing dangling commas (they’re only a problem if you leave them in when targeting \<IE8) and there is the disadvantage of greater VCS churn if they are prohibited.
See the comment at http://eslint.org/docs/rules/comma-dangle
In writing PR #13, I added a line to an array and had to edit two lines instead of 1 because of the eslint rule which is set to never instead of always. Since you’re transpiling anyway, I don’t see the benefit to disallowing dangling commas (they’re only a problem if you leave them in when targeting \<IE8) and there is the disadvantage of greater VCS churn if they are prohibited.