why does JS backend return array with object?

[Araq]

The usage of arrays in this context is to emulate pointers and the codegen 
sometimes needs pointers so that Nim's semantics can work. Consider:
    
    
    proc mutate(x: var int) = x = 4
    var global: int
    mutate(global)
    
    
    Run

The code generator sometimes does this where it would not be required but it's 
hard to do better and to ensure correctness at the same time.