用javascript如何实现菜单隐藏？

http://community.csdn.net/expert/deeptree/dtbar.asp?xmlsrc=/Expert/deeptree/Rooms/List.xml&csdnstyle=0&myie=ie<script language="javascript">var strColumns_Current = "215,*";function movenext()
  {
  top.deeptree.movenext();
  }function moveprevious()
  {
  top.deeptree.moveprevious();
  }function hidetoc()
  {
  strColumns_Current = top.mainframeset.cols
  
  top.mainframeset.cols = "1,*";
  top.contentbar.document.all("showtoc").style.display = "block";
  }function showtoc()
  {
  top.mainframeset.cols = strColumns_Current;
  top.contentbar.document.all("showtoc").style.display = "none";
  }
  
function synctoc()
{
    top.location = top.location.pathname + "?url=" + top.content.location.pathname + top.content.location.search + top.content.location.hash;
}function displaybutton()
  {
  document.all.showtoc.style.display = "block";
  }function mouseover(item)
  {
  switch (item)
    {
    case "moveprevious" :
      window.status = "移动到菜单上一项 [SHIFT + TAB]";
      document.all.imgMovePrevious.src = "Images/moveprevious2.gif";
      break;    case "movenext" :
      window.status = "移动到菜单下一项 [TAB]";
      document.all.imgMoveNext.src = "Images/movenext2.gif";
      break;    case "synctoc" :
      window.status = "同步菜单中的当前页";
      document.all.imgSyncToc.src = "Images/synctoc2.gif"
      break;    case "hidetoc" :
      window.status = "隐藏菜单";
      document.all.imgHideToc.src = "Images/hidetoc2.gif"
      break;
    }  }function mouseout(item)
  {
  switch (item)
    {
    case "moveprevious" :
      window.status = "";
      document.all.imgMovePrevious.src = "Images/moveprevious1.gif";
      break;    case "movenext" :
      window.status = "";
      document.all.imgMoveNext.src = "Images/movenext1.gif";
      break;    case "synctoc" :
      window.status = "";
      document.all.imgSyncToc.src = "Images/synctoc1.gif"
      break;    case "hidetoc" :
      window.status = "";
      document.all.imgHideToc.src = "Images/hidetoc1.gif"
      break;
    }
  }function selectstart()
  {
  window.event.cancelBubble = true;
  window.event.returnValue = false;
  return false;
  }</script><html><head>
<META NAME="Robots" CONTENT="noindex">
        <meta content="text/html;charset=gb2312" http-equiv="Content-Type">
<script src="/Expert/style/get_css.js"></script>
  <title>Deeptree Controlbar</title>
</head><body onselectstart="selectstart();" topmargin="0" leftmargin="0" marginheight="0" marginwidth="0" class="color2">  <table width="100%" border="0" cellpadding="0" cellspacing="0">
    <tr>
      <td align="left">
        <table border="0" cellpadding="0" cellspacing="0">
          <tr>
            <td height="20" width="4"></td>
            <td height="20"><img id="imgMoveNext" style="cursor:hand" onmouseover="mouseover('movenext');" onmouseout="mouseout('movenext')" onclick="movenext();" title="移动到菜单下一项 [TAB]" src="Images/movenext1.gif" border="0" /></td>
            <td height="20" width="2"></td>
            <td height="20"><img id="imgMovePrevious" style="cursor:hand" onmouseover="mouseover('moveprevious');" onmouseout="mouseout('moveprevious')" onclick="moveprevious();" title="移动到菜单上一项 [SHIFT + TAB]" src="Images/moveprevious1.gif" border="0" /></td>
            <td height="20" width="8"></td>
          </tr>
        </table>
      </td>
      <td align="right">
        <table border="0" cellpadding="0" cellspacing="0">
          <tr>
            <td height="20"><img id="imgSyncToc" style="cursor:hand" onclick="synctoc();" onmouseover="mouseover('synctoc');" onmouseout="mouseout('synctoc');" src="Images/synctoc1.gif" title="同步菜单中的当前页" /></td>
            <td height="20" width="10"><img src="Images/1pix.gif" width="10" height="20"></td>
            <td height="20"><img id="imgHideToc" style="cursor:hand" onclick="hidetoc();" onmouseover="mouseover('hidetoc');" onmouseout="mouseout('hidetoc');" src="Images/hidetoc1.gif" title="隐藏菜单" /></td>
            <td height="20" width="4"><img src="Images/1pix.gif" width="4" height="20"></td>
          </tr>
        </table>
      </td>
    </tr>
  </table></body>
</html>