JS隐藏显示左侧菜单

<script language="javascript" type="text/javascript">

    function HideShow()

    {

        var alt = document.getElementById('switchPoint').alt;

        var src = document.getElementById('switchPoint').src;

        if (alt == "隐藏")

        {

            document.getElementById('switchPoint').alt = "显示";

            document.getElementById('switchPoint').src = src.substring(0, src.length - 8) + "show.jpg";

            document.all("leftFrame").style.display = "none";

        }

        else

        {

            document.getElementById('switchPoint').alt = "隐藏";

            document.getElementById('switchPoint').src = src.substring(0, src.length - 8) + "hide.jpg";

            document.all("leftFrame").style.display = "";

        }

    }

</script>

<table border="0" cellpadding="0" cellspacing="0" width="100%" style="height: 100%">

                <tr>

                    <td bgcolor="#0A5C8E" width="8px">

                         </td>

                    <td width="170px" valign="top" id="leftFrame">  

                        <uc2:left ID="left1" runat="server" />

                    </td>

                    <td bgcolor="#0A5C8E" width="10px">

                        <img src="images/hide.jpg" alt="隐藏" id="switchPoint" onclick="HideShow()" style="cursor:hand"/>

                    </td>

                    <td align="left" valign="top" height="620px">

                        <iframe id="rightFrame" name="main" frameborder="0" scrolling="yes"  src="main.aspx" height="100%" width="100%" ></iframe>

                         </td>

                    <td bgcolor="#0A5C8E" width="8px">

                         </td>

                </tr>

</table>