jquery – 如果没有足够的空间,如何使superfish菜单向后打开？

var windowWidth;
$(document).ready(function (){
        windowWidth= $(window).width();
        $( window ).resize(function() {
            windowWidth = $(window).width();
        });

        $('.Top-Nav').superfish({
            onBeforeShow : function (){                 
                if(!this.is('.Top-Nav>li>ul')){
                    var subMenuWidth = $(this).width();
                    var parentLi = $(this).parent();                    
                    var parentWidth = parentLi.width();
                    var subMenuRight = parentLi.offset().left + parentWidth + subMenuWidth;
                    if(subMenuRight > windowWidth){
                        $(this).css({'left': 'auto','right': parentWidth+'px'});
                    } else {
                        $(this).css({'left': '','right': ''});
                    }
                }
            }
        });
 });