JS片段：
<script>
//初始化
var def="1";
function mover(object){
  //主菜单
  var mm=document.getElementById("m_"+object);
  mm.className="m_li_a";
  //初始主菜单先隐藏效果
  if(def!=0){
    var mdef=document.getElementById("m_"+def);
    mdef.className="m_li";
  }
  //子菜单
  var ss=document.getElementById("s_"+object);
  ss.style.display="block";
  //初始子菜单先隐藏效果
  if(def!=0){
    var sdef=document.getElementById("s_"+def);
    sdef.style.display="none";
  }
}

function mout(object){
  //主菜单
  var mm=document.getElementById("m_"+object);
  mm.className="m_li";
  //初始主菜单还原效果
  if(def!=0){
    var mdef=document.getElementById("m_"+def);
    mdef.className="m_li_a";
  }
  //子菜单
  var ss=document.getElementById("s_"+object);
  ss.style.display="none";
  //初始子菜单还原效果
  if(def!=0){
    var sdef=document.getElementById("s_"+def);
    sdef.style.display="block";
  }
}
</script>