function mousewheel(obj,fn){

                obj.onmousewheel===null ? obj.onmousewheel=fun : obj.addEventListener('DOMMouseScroll',fun,false);

                function fun(e){

                    var e=e || event,

                        num=0;

                    if(e.wheelDelta){

                        num=e.wheelDelta>0?1:-1;

                    }else{

                        num=e.detail<0?1:-1;

                    }

                    fn(num);

                    if(e.preventDefault)e.preventDefault();

                    return false;

                }

            }

            var oDiv=document.getElementById('div');

            mousewheel(oDiv,function(dir){

                if(dir>0) alert('向上滚动');

                if(dir<0) alert('往下滚动');

            });