// javascript document

 window.onload=displaymenu;
 function displaymenu(){
 //获取菜单id
   var menu=getid("menu");
   
  //隐藏2级菜单和3级
  // for(var i=0;i<gettns(menu,"ul").length;i++){
//     gettns(menu,"ul")[i].style.display="none";
//   }
  
  //获取菜单所有li
 var menu_li_1=gettns(menu,"li");
  //隐藏显示菜单
 for(var i=0;i<menu_li_1.length;i++){
  if(menu_li_1[i].getelementsbytagname("ul").length>0){
    menu_li_1[i].onmouseover=displaychildmenu;
 menu_li_1[i].onmouseout=disappearchildmenu;
  }
 }
 }
 //获取id函数
 function getid(elem){
   return document.getelementbyid(elem);
 }
 //获取tagname
 function gettns(elem,name){
   return (elem || document).getelementsbytagname(name);
 }
 //显示菜单函数
 function displaychildmenu(){
   gettns(this,"ul")[0].style.display="block";
 } 
 //隐藏菜单函数
 function disappearchildmenu(){
   for(var i=0;i<gettns(this,"ul").length;i++){
    gettns(this,"ul")[i].style.display="none";
   }
 }