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
 };
}();