I had to check, does it toposort? But no, it's ordered:
> example = ({ w = h * 2, h = w * 2 }) => ({w,h})
> example({w:10})
{ w: 10, h: 20 }
> example({h:10})
ReferenceError: Cannot access 'h' before initialization
> example({})
ReferenceError: Cannot access 'h' before initialization