>>Thierry gave you the best solution (but ignored your requirement to use more lines :-})
>
>several lines? OK
>

>return 0
>  || loWindow.pageYOffset
>  || document.documentElement.scrollTop
>  || document.body.scrollTop
>  || 0;
>

>
>;)

Cheating. Only one semi-colon therefore only one line :-}