js 捕捉滚轮的滚动

滚动方向区分为正负：
<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title></title>
    <script type="text/javascript">
       window.onload = function(){
           //去掉默认的contextmenu事件，否则会和右键事件同时出现。
           document.oncontextmenu = function(e){
               e.preventDefault();
           };
           document.getElementById("test").onmousedown = function(e){
               if(e.button ==2){
                   alert("你点了右键");
               }else if(e.button ==0){
                   alert("你点了左键");
               }else if(e.button ==1){
                   alert("你点了滚轮");
               }
           }
       }
    </script>
</head>
<body>
 <label for="wheelDelta">滚动值:</label>(IE/Opera)<input type="text" id="wheelDelta"/> 
<label for="detail">滚动值:(Firefox)</label><input type="text" id="detail"/> 
<script type="text/javascript"> 
var scrollFunc=function(e){ 
    ee=e || window.event; 
    var t1=document.getElementById("wheelDelta"); 
    var t2=document.getElementById("detail"); 
    if(e.wheelDelta){//IE/Opera/Chrome 
        t1.value=e.wheelDelta; 
    }else if(e.detail){//Firefox 
        t2.value=e.detail; 
    } 
} 
/*注册事件*/ 
if(document.addEventListener){ 
    document.addEventListener('DOMMouseScroll',scrollFunc,false); 
}//W3C 
window.onmousewheel=document.onmousewheel=scrollFunc;//IE/Opera/Chrome 
</script>
<div style=" 400px;height:400px;margin:auto;border:1px solid pink" id="test"></div>
</body>
</html>