تمرير ال Id الى Parameter داخل Function

<script type ="text/javascript" >
function chkcase(partxt)
{

if (document.getElementById(partxt).value.length == 0)
{

document.getElementById("<%=Button1.ClientID %>").disabled =true;

}
else
{

document.getElementById("<%=Button1.ClientID %>").disabled = false;


}

}
</script>

<table id="tabl1" style="width: 100%">
<tr>
<td align="left" dir="ltr" style="width: 119px">
<asp:Label ID="Label1" runat="server" Text="Char string"></asp:Label>
</td>
<td style="width: 198px">
<asp:TextBox ID="txt_char" runat="server" Width="173px" onchange= "chkcase(this.id);"></asp:TextBox>

</td>
<td style="width: 74px">
<asp:Button ID="Button1" runat="server" Text="Button" Width="67px"
OnClientClick="myfunction('mainpanl');" Enabled="False" />
</td>
<td align="left" style="width: 213px">
<asp:Label ID="Label4" runat="server" Text="Drop Down"></asp:Label>
</td>
<td style="width: 161px">
<asp:DropDownList ID="DropDownList1" runat="server" Height="16px" Width="165px">
</asp:DropDownList>
</td>
<td rowspan="4">
<asp:ListBox ID="ListBox1" runat="server" Width="118px" ></asp:ListBox>
</td>
</tr>
<tr>
<td style="width: 119px">
 </td>
<td style="width: 198px">
 </td>
<td style="width: 74px">
 </td>
<td style="width: 213px">
 </td>
<td style="width: 161px">
 </td>
</tr>
<tr>
<td align="left" style="width: 119px">
<asp:Label ID="Label2" runat="server" Text="Char Num"></asp:Label>
</td>
<td style="width: 198px">
<asp:TextBox ID="Txt_num" runat="server" Width="172px"></asp:TextBox>
</td>
<td align="left" style="width: 74px">
<asp:Label ID="Label3" runat="server" Text="Char Date"></asp:Label>
</td>
<td style="width: 213px">
<asp:TextBox ID="txt_date" runat="server" Width="208px"></asp:TextBox>
</td>
<td style="width: 161px">
 </td>
</tr>
<tr>
<td style="width: 119px">
 </td>
<td style="width: 198px">
 </td>
<td style="width: 74px">
 </td>
<td style="width: 213px">
 </td>
<td style="width: 161px">
 </td>
</tr>
</table>