js特效,页面下雪的小例子

if (arr[i]){
                var ofs=$(this).offset();
                var x=parseInt(ofs.left);
                var y =parseInt(ofs.top);
                var vy=parseInt($(this).attr("vy"));
                x +=wind;
                vy *= ay;
                y+= vy;
                $(this).offset({"top":y});
                $(this).offset({"left":x});
                if(y>winHeight){
                    $(this).remove();
                    delete arr[i];
                }