如何实现jquery div滚动条效果？jquery滚动条入门例子

<script type="text/javascript" src="js/jquery-1.4.2.min.js"></script>  
<script type="text/javascript">  
var check = false;//是否可移动 
$(document).ready(function(){ 
var h = $("#scrollContent").height(); 
var ih = $("#divcontent").height(); 
var mh = parseInt(h*h/ih); 
var h1 = parseInt($("#ypThumbContainer").height())-mh;//图片与div的高度差值 
var h2 = parseInt(ih - h);//内容与边框div的高度差值 
 
$("#scrollContent").hover(function(){ 
if(ih > h){ 
$("#ypThumbContainer").show("slow"); 
$("#ypThumb").find("img").height(mh); 
$("#ypThumb").show("slow"); 
 
//begin 
var oDiv = document.getElementById("ypThumbContainer"); 
var oDiv2 = document.getElementById("ypThumb"); 
var mouseStart={}; 
var divStart={}; 
var rightStart={}; 
var bottomStart={}; 
 
$(oDiv2).mousedown(function(ev){ 
var oEvent = ev||event; 
mouseStart.x = oEvent.clientX; 
mouseStart.y = oEvent.clientY; 
divStart.x = parseInt($(oDiv2).css("left")); 
divStart.y = parseInt($(oDiv2).css("top")); 
 
if(oDiv2.setCapture){ 
oDiv2.setCapture(); 
oDiv2.onmousemove = doDrag3; 
oDiv2.onmouseup = stopDrag3; 
}else{ 
$(oDiv).bind("mousemove",doDrag3).bind("mouseup",stopDrag3); 
} 
oEvent.preventDefault(); 
}); 
 
function doDrag3(ev) { 
var oEvent = ev||event; 
var t = oEvent.clientY-mouseStart.y+divStart.y; 
if(t < 0){ 
t = 0; 
 
}else if(t >= $(oDiv).height()-$(oDiv2).height()){ 
t = $(oDiv).height()-$(oDiv2).height(); 
} 
$(oDiv2).css("top",t+"px"); 
$("#divcontent").css("top",-(t*h2/h1)+"px"); 
} 
 
function stopDrag3(){ 
if(oDiv2.releaseCapture){ 
oDiv2.releaseCapture(); 
oDiv2.onmousemove = null; 
oDiv2.onmouseup = null; 
}else{ 
$(oDiv).unbind("mousemove",doDrag3).unbind("mouseup",stopDrag3); 
} 
} 
//end 
} 
},function(){ 
$("#ypThumbContainer").hide("slow"); 
$("#ypThumb").hide("slow"); 
 }); 
}); 
</script> 
 

<div style="width:150px;overflow:hidden;height:170px;border:1px #000 solid;z-index:1; position:relative;" id="scrollContent"> 
<div class="thumbContainer" id="ypThumbContainer" style="Z-INDEX: 3; right:0px; WIDTH: 9px; POSITION: absolute; TOP: 0px; HEIGHT: 170px;border:1px #000 solid; display:none"> 
  <div class="thumb" id="ypThumb" style="POSITION: absolute; TOP: 0px; BACKGROUND-COLOR: #ffd200;"> 
<img class="thumbImg" id="ypThumbImg" height="50" src="images/thumb.gif" width="9" style="cursor:pointer;"/><br /> 
</div> 
</div> 
<div id="divcontent" style="position:absolute;"> 
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