Brackets inline editor comes to mind. Just replace CSS definitions with function definitions (I think it might already do this for ?) The zooming functionality

Brackets inline editor comes to mind. Just replace CSS definitions with function definitions (I think it might already do this for ?) The zooming functionality you're thinking about probably wouldn't be very practical. (Zooming in down to opcode or out to high level framework calls.) But simply being able to inspect definition inline would do.