Use of computed property changes object key order
$ cat computed_prop.js
var x = "computed"; console.log(JSON.stringify({ [x]:1, foo:2 }));
$ cat computed_prop.js | node
{"computed":1,"foo":2}
$ cat computed_prop.js | bin/buble | node
{"foo":2,"computed":1}
Probably not a big deal, although some applications depending on key order would break.