jq 滾輪監聽事件

windowAddMouseWheel();  
function windowAddMouseWheel() { 
    var i = 0;
    var scrollFunc = function (e) {
        e = e || window.event;  
        if (e.wheelDelta) {  //判斷瀏覽器IE，谷歌滑輪事件  
            if (e.wheelDelta > 0) { //當滑輪向上滾動時  
                alert("滑輪向上滾動"+i);  
            }  
            if (e.wheelDelta < 0) { //當滑輪向下滾動時  
                alert("滑輪向下滾動");  
            }  
        } else if (e.detail) {  //Firefox滑輪事件  
            if (e.detail> 0) { //當滑輪向上滾動時  
                i++;
                window.scrollTo(0,300*i);
                alert("滑輪向上滾動"+i);  
            }  
            if (e.detail< 0) { //當滑輪向下滾動時  
                i--;
                window.scrollTo(0,300*i);
                alert("滑輪向下滾動"+i);  
            }  
        }  
    };  
    //給頁面綁定滑輪滾動事件  
    if (document.addEventListener) {  
        document.addEventListener('DOMMouseScroll', scrollFunc, false);  
    }  
//滾動滑輪觸發scrollFunc方法  
    window.onmousewheel = document.onmousewheel = scrollFunc;  
}