JS 判断鼠标滚轮的上下滚动

<script type="text/javascript">  
        var scrollFunc = function (e) {  
        e = e || window.event;  
        if (e.wheelDelta) {  //判断浏览器IE，谷歌滑轮事件               
            if (e.wheelDelta > 0) { //当滑轮向上滚动时  
                alert("滑轮向上滚动");  
            }  
            if (e.wheelDelta < 0) { //当滑轮向下滚动时  
                alert("滑轮向下滚动");  
            }  
        } else if (e.detail) {  //Firefox滑轮事件  
            if (e.detail> 0) { //当滑轮向上滚动时  
                alert("滑轮向上滚动");  
            }  
            if (e.detail< 0) { //当滑轮向下滚动时  
                alert("滑轮向下滚动");  
            }  
        }  
    }  
    //给页面绑定滑轮滚动事件  
    if (document.addEventListener) {//firefox  
        document.addEventListener('DOMMouseScroll', scrollFunc, false);  
    }  
    //滚动滑轮触发scrollFunc方法  //ie 谷歌  
    window.onmousewheel = document.onmousewheel = scrollFunc;   
    </script>