var menu = function(){
 var t = 15, z = 50, s = 6, a;
 function sl(c, f){
 var h = c.offsetHeight;
 if ((h <= 0 && f != 1) || (h >= c.mh && f == 1)) {
 if (f == 1) {
 c.style.filter = '';
 c.style.opacity = 1;
 c.style.overflow = 'visible';
 }
 clearInterval(c.t);
 return
 }
 var d = (f == 1) ? Math.ceil((c.mh - h) / s) : Math.ceil(h / s), o = h / c.mh;
 c.style.opacity = o;
 c.style.filter = 'alpha(opacity=' + (o * 100) + ')';
 c.style.height = h + (d * f) + 'px';
 };
 function dd(n){
 this.h = [];//存取有子菜单的项目
 this.c = [];//存取子菜单
 };
 dd.prototype = {
 init: function(p, c){
 a = c;
 var that = this;
 var w = document.getElementById(p), s = w.getElementsByTagName('ul'), l = s.length/*二级菜单的个数*/, i = 0;
 for (i; i < l; i++) {
 var h = s[i].parentNode;
 this.h[i] = h;
 this.c[i] = s[i];
 /*
 * 重点就在这里，一点JS的语法技巧，通过闭包来实现对i（索引的传递）
 * 然后就是Javascript里比较奇怪的一点，必须在内部的函数之外声明that=this
 * 这样对象的作用域才可以保持，很奇怪，但是很有效
 */
 h.onmouseover = function(index){
 return function(){
 that.st(index, true);
 }
 }(i);
 h.onmouseout = function(index){
 return function(){
 that.st(index, false);
 }
 }(i);
 }
 },
 st: function(x, f){
 var c = this.c[x], h = this.h[x], p = h.getElementsByTagName('a')[0];
 if (c.t) {
 clearInterval(c.t);
 }
 c.style['overflow'] = 'hidden';
 if (f) {
 p.className += ' ' + a;
 if (!c.mh) {
 c.style.display = 'block';
 c.style.height = '';
 c.mh = c.offsetHeight;
 c.style.height = 0;
 }
 if (c.mh == c.offsetHeight) {
 c.style.overflow = 'visible';
 }
 else {
 c.style.zIndex = z;
 z++;
 c.t = setInterval(function(){
 sl(c, 1)
 }, t);
 }
 }
 else {
 p.className = p.className.replace(a, '');
 c.t = setInterval(function(){
 sl(c, -1)
 }, t);
 }
 }
 };
 return {
 dd: dd
 };
}();