鼠标按钮

getButton: function(event){//鼠标按钮兼容
                if (document.implementation.hasFeature('MouseEvents','2.0'))//标准下
                {
                    return event.button;
                }else {
                    switch (event.button)//非标准下
                    {
                    case 0:
                    case 1:
                    case 3:
                    case 5:
                    case 7:
                        return 0;
                    case 2:
                    case 6:
                        return 2;
                    case 4:
                        return 1;
                    }
                }
            }