上下滚动广告

(function($){
    $.fn.extend({
        rollList:function(option){
            option=$.extend({
                direction:"up",
                step:1,
                time:23
            },option);
            var step_coe,scroll_coe,score_coe;
            if(option.direction=="up")
            {
                step_coe=1;
                scroll_coe=1;
                score_coe=1;
            }else
            {
                step_coe=-1;
                scroll_coe=-1;
                score_coe=0;
            }
            return this.each(function(){
                var $this=$(this);
                var _this=this;
                var itemHeight;
                var temp=$("
 
");
                $this.css("overflow","hidden").children()
                    .appendTo(temp);
                $this.append(temp.clone(true)).append(temp);
                itemHeight=$this.children();
                itemHeight=itemHeight.eq(1).offset().top-itemHeight.eq(0).offset().top;
                while($this.children(":last").offset().top-$this.offset().top<=$this.height())
                    $this.append(temp.clone(true));
                var roll;
                this.scrollTop=itemHeight*(1-score_coe);
                roll=function (){
                    temp=setInterval(function(){
                        if(_this.scrollTop*scroll_coe>=itemHeight*score_coe)
                        {	
                        _this.scrollTop=(_this.scrollTop-itemHeight)*scroll_coe;
                        }
                        _this.scrollTop+=option.step*step_coe;

                    },option.time);
                }
                $this.hover(function(){
                    clearInterval(temp);
                },function(){
                    roll();	
                });
                roll();
            });
        }		
    })
}(jQuery));

调用如下：
$(elem).rollList();