二级菜单的实现方法

.nav li:hover ul{
display: block;
width: 100px;
/*如果不写宽度，就会水平排列*/
padding: 0;
}
.nav li:hover ul li ul{
display: none;
/*隐藏三级菜单的*/
}

var tool = new Tool;
var oDiv2 = document.getElementById("div2");
document.onmouseover = function (e) {
    e = e || window.event;//处理事件兼容性；
var tar = e.target || e.srcElement;//事件源；
var xiaomi = tar.getAttribute("xiaomi");//监听的对象；
var ch = tool.getCss("height", oDiv2);
if (xiaomi === "true") {//以属性来判断；
if (ch <= 200) {
move.call(oDiv2, 200)
        }
    } else {
if (ch > 0) {
move.call(oDiv2, 0)
        }

    }
};
function move(target) {
var that = this;
_move();
function _move() {
var start = tool.getCss("height", that);//要在内部，不能写在外面
clearTimeout(that.timer);
that.timer = setTimeout(_move, 10);
if (start >= target) {
tool.setCss(that, "height", start - 10);
if (start - 10 < target) {
tool.setCss(that, "height", target);
return;
            }
        } else if (start < target) {
tool.setCss(that,"height", start + 10);
if (start + 10 >= target) {
tool.setCss(that, "height", target);
return;
            }
        } else {
return;
        }
    }
}