I often wonder what the disadvantage is of moving to an existing, established, understood and already tooled language (such as the ActionScript family) if one is seeking to migrate away from a legacy language such as JavaScript.

Now I am using ActionScript to make a point, since I have not yet programmed in it to be able to address how much Dart does or does not mimic the AS syntax.

Is ActionScript "type-optional" as with Dart?