For instance, the basic fizzbuzz example provided on the main page looks very similar, but doesn't actually run in anarki. Maybe that's anarki's fault, but the syntax of the for loop is different.
I do like the idea of arc ported to js though; makes getting access to mongodb easier, at the very least :)
In general, worrying about compatibility in the arc/anarki neighborhood is a fool's errand. Not worth doing. Just do what makes sense, and don't be afraid to be different.
In this particular case it would be nice to have consistency on both ends. Though I guess the best way to achieve that is probably with node.