You could always invert it. Any situation that requires a lot of logic but not much interfacing could be handled with haXe - maybe you need a particular algorit

You could always invert it. Any situation that requires a lot of logic but not much interfacing could be handled with haXe - maybe you need a particular algorithm, in JS and C++. Rather than try to interface with JS or C++ in Haxe, could you "write once" the library you need in Haxe, compile it down, and interface with it?