jquery 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=$("<DIV> </DIV>"); 
$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));

$(elem).rollList();