function wheelUp() {
    alert("wheelUp");
}
function wheelDown() {
    alert("wheelDown");
}
wheel(wheelUp, wheelDown);

// 滚轮响应事件
// 参数:type有两个属性值,分别为"up"(滚轮向上)和"down"(滚轮向下)
function wheel(upFn, downFn) {
	// IE6
	window.onmousewheel = getWheelDalta;
	// Firefox
	if(window.addEventListener) {
		window.addEventListener("DOMMouseScroll", getWheelDalta, false);
	}
	// 获得鼠标滚轮事件
	function getWheelDalta(event) {
		var event = event || window.event;
	    var delta = 0;
	    // delta的返回值为正时,表示向前滚动;delta的返回值为负时,表示向后滚动;
	    if (event.wheelDelta) {
	    	// IE中,鼠标滚轮信息存放在wheelDelta属性中;向前滚动时,wheelDelta的值是120的倍数;向后滚动时,wheelDelta的值是-120的倍数;
	        delta = event.wheelDelta/120; 
	        if (window.opera) delta = -delta;
	    } else if (event.detail) {
	    	// Firefox的鼠标滚轮信息存放在detail属性中;向前滚动,detail的值是-3的倍数;向后滚动,detail的值是3的倍数;
	        delta = -event.detail/3;
	    }
	    // 执行滚轮事件函数
	    if(delta > 0) {
	    	upFn();
	    }else {
	    	downFn();
	    }

		// 阻止默认行为,防止当页面本身就存在滚动条时出现的异常
		prevent(event);
		function prevent(evt){
			if(evt.preventDefault){
				evt.preventDefault();
			}else{
				evt.returnValue = false;
			}
		}
	}   
}

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