此实例通过对滚轮事件的监听，通过滚轮控制滚动条的上下移动，可以将其修改后运用与使用滚轮缩放图片、改变透明度等特效。
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title></title>
<style type="text/css">
*{
margin: 0;
padding: 0;
}
#boxwrap{
position: relative;
width: 15px;
height: 500px;
margin: 50px auto;
box-sizing: border-box;
border: 1px solid gainsboro;
border-radius: 6px;
}
#box{
position: absolute;
left: 0px;
top: 0px;
width: 13px;
height: 30px;
background: gray;
border-radius: 6px;
}
</style>
<script type="text/javascript">
window.onload = function (){
var boxwrp = document.getElementById('boxwrap');
var box = document.getElementById('box');
//兼容firefox
if(boxwrp.addEventListener){
document.addEventListener("DOMMouseScroll", fn, false);
}
document.onmousewheel = fn;//兼容IE、chrome
function fn(ev){
var ev = ev||event;
var bool = false;
//IE、chrome 向上：120，向下：-120
if(ev.wheelDelta){
bool= ev.wheelDelta > 0? true : false;
}
//firefox 向上：-3，向下：3
else{
bool= ev.detail < 0? true : false;
}
if(bool){
if(box.offsetTop>=10){
box.style.top = box.offsetTop - 10 + "px";
}
else{
box.style.top = 0;
}
}
else{
if(box.offsetTop<=boxwrp.offsetHeight-box.offsetHeight-10){
box.style.top = box.offsetTop + 10 + "px";
}
else{
box.style.top = boxwrp.offsetHeight - box.offsetHeight + "px";
}
}
}
}
</script>
</head>
<body>
<div id="boxwrap">
<div id="box"></div>
</div>
</body>
</html>
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