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>