基于JavaScript实现自定义滚动条

可直接使用的js滚动条，先看看效果图：

代码如下

<!DOCTYPE html>
<html lang="en">
<head>
 <meta charset="UTF-8">
 <title>自定义滚动条</title>
</head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>滚动条</title>
<style type="text/css">
*{ margin:0; padding:0;}
#mainBox{ 
 width:400px; 
 height:500px; 
 border:1px #bbb solid; 
 position:relative; 
 overflow:hidden;
  margin:50px auto;
 }
#content{ 
 height:2500px; 
 position:absolute; 
 left:0; 
 top:0; 
 background:url(https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1485320653275&di=b7bc29cc2c7b3388d44958d8f97db0a3&imgtype=0&src=http%3A%2F%2Fphotocdn.sohu.com%2F20151212%2Fmp48094209_1449905365456_7.jpg) 
}
.scrollDiv{
 width:18px; 
 position:absolute; 
 top:0; 
 background:#666;
 border-radius:10px;
}
</style>
</head>
<body>
<div id="mainBox">
 <div id="content"></div>
</div>
<script type="text/javascript">
var doc=document;
var _wheelData=-1;
var mainBox=doc.getElementById('mainBox');
function bind(obj,type,handler){
 var node=typeof obj=="string"?$(obj):obj;
 if(node.addEventListener){
 node.addEventListener(type,handler,false);
 }else if(node.attachEvent){
 node.attachEvent('on'+type,handler);
 }else{
 node['on'+type]=handler;
 }
}
function mouseWheel(obj,handler){
 var node=typeof obj=="string"?$(obj):obj;
 bind(node,'mousewheel',function(event){
 var data=-getWheelData(event);
 handler(data);
 if(document.all){
 window.event.returnValue=false;
 }else{
 event.preventDefault();
 }
 });
 //火狐
 bind(node,'DOMMouseScroll',function(event){
 var data=getWheelData(event);
 handler(data);
 event.preventDefault();
 });
 function getWheelData(event){
 var e=event||window.event;
 return e.wheelDelta?e.wheelDelta:e.detail*40;
 }
}
function addScroll(){
 this.init.apply(this,arguments);
}
addScroll.prototype={
 init:function(mainBox,contentBox,className){
 var mainBox=doc.getElementById(mainBox);
 var contentBox=doc.getElementById(contentBox);
 var scrollDiv=this._createScroll(mainBox,className);
 this._resizeScorll(scrollDiv,mainBox,contentBox);
 this._tragScroll(scrollDiv,mainBox,contentBox);
 this._wheelChange(scrollDiv,mainBox,contentBox);
 this._clickScroll(scrollDiv,mainBox,contentBox);
 },
 //创建滚动条
 _createScroll:function(mainBox,className){
 var _scrollBox=doc.createElement('div')
 var _scroll=doc.createElement('div');
 var span=doc.createElement('span');
 _scrollBox.appendChild(_scroll);
 _scroll.appendChild(span);
 _scroll.className=className;
 mainBox.appendChild(_scrollBox);
 return _scroll;
 },
 //调整滚动条
 _resizeScorll:function(element,mainBox,contentBox){
 var p=element.parentNode;
 var conHeight=contentBox.offsetHeight;
 var _width=mainBox.clientWidth;
 var _height=mainBox.clientHeight;
 var _scrollWidth=element.offsetWidth;
 var _left=_width-_scrollWidth;
 p.style.width=_scrollWidth+"px";
 p.style.height=_height+"px";
 p.style.left=_left+"px";
 p.style.position="absolute";
 p.style.background="#ccc";
 contentBox.style.width=(mainBox.offsetWidth-_scrollWidth)+"px";
 var _scrollHeight=parseInt(_height*(_height/conHeight));
 if(_scrollHeight>=mainBox.clientHeight){
 element.parentNode.style.display="none";
 }
 element.style.height=_scrollHeight+"px";
 },
 //拖动滚动条
 _tragScroll:function(element,mainBox,contentBox){
 var mainHeight=mainBox.clientHeight;
 element.onmousedown=function(event){
 var _this=this;
 var _scrollTop=element.offsetTop;
 var e=event||window.event;
 var top=e.clientY;
 //this.onmousemove=scrollGo;
 document.onmousemove=scrollGo;
 document.onmouseup=function(event){
 this.onmousemove=null;
 }
 function scrollGo(event){
 var e=event||window.event;
 var _top=e.clientY;
 var _t=_top-top+_scrollTop;
 if(_t>(mainHeight-element.offsetHeight)){
  _t=mainHeight-element.offsetHeight;
 }
 if(_t<=0){
  _t=0;
 }
 element.style.top=_t+"px";
 contentBox.style.top=-_t*(contentBox.offsetHeight/mainBox.offsetHeight)+"px";
 _wheelData=_t;
 }
 }
 element.onmouseover=function(){
 this.style.background="#444"; 
 }
 element.onmouseout=function(){
 this.style.background="#666"; 
 }
 },
 //鼠标滚轮滚动，滚动条滚动
 _wheelChange:function(element,mainBox,contentBox){
 var node=typeof mainBox=="string"?$(mainBox):mainBox;
 var flag=0,rate=0,wheelFlag=0;
 if(node){
 mouseWheel(node,function(data){
 wheelFlag+=data;
 if(_wheelData>=0){
  flag=_wheelData;
  element.style.top=flag+"px";
  wheelFlag=_wheelData*12;
  _wheelData=-1;
 }else{
  flag=wheelFlag/12;
 }
 if(flag<=0){
  flag=0;
  wheelFlag=0;
 }
 if(flag>=(mainBox.offsetHeight-element.offsetHeight)){
  flag=(mainBox.clientHeight-element.offsetHeight);
  wheelFlag=(mainBox.clientHeight-element.offsetHeight)*12;
 }
 element.style.top=flag+"px";
 contentBox.style.top=-flag*(contentBox.offsetHeight/mainBox.offsetHeight)+"px";
 });
 }
 },
 _clickScroll:function(element,mainBox,contentBox){
 var p=element.parentNode;
 p.onclick=function(event){
 var e=event||window.event;
 var t=e.target||e.srcElement;
 var sTop=document.documentElement.scrollTop>0?document.documentElement.scrollTop:document.body.scrollTop;
 var top=mainBox.offsetTop;
 var _top=e.clientY+sTop-top-element.offsetHeight/2;
 if(_top<=0){
 _top=0;
 }
 if(_top>=(mainBox.clientHeight-element.offsetHeight)){
 _top=mainBox.clientHeight-element.offsetHeight;
 }
 if(t!=element){
 element.style.top=_top+"px";
 contentBox.style.top=-_top*(contentBox.offsetHeight/mainBox.offsetHeight)+"px";
 _wheelData=_top;
 }
 }
 }
}

new addScroll('mainBox','content','scrollDiv');
</script>
</body>
</html>

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