Validate at least one of two TextBox

Hi

try these examples :

<script type="text/javascript" language="javascript">
   
     function checkInput()
     {
       var tb1 = document.getElementById('<%= TextBox1.ClientID %>');
       var tb2 = document.getElementById('<%= TextBox2.ClientID %>');
            if( tb1.value == "" && tb2.value == "")
            {
               alert('TextBox cannot be emplty!');
               return false;

            }
            else
            {return true;}
     }
    </script>

<asp:Button ID="Button1" runat="server" Text="Button" OnClientClick="return checkInput();" />

//——or

<script type="text/javascript">
        function validateControls(txt1, txt2)
        {
            if (document.getElementById(txt1).value == '' && document.getElementById(txt2).value == '')
            {
                alert('Atleaset one value required.');
                return false;
            }
            else
                return true;
        }
    </script>

and the button that submits the page or on which you want to validate the textboxes you can add an attribute like this

this.Button1.Attributes.Add("onclick", "javascript: return validateControls('" + TextBox1.ClientID + "', '" + TextBox2.ClientID + "')");

//– or using CustomValidator Control

<script type="text/javascript" language="javascript">
     function checkInput(source, args)
     {
       var tb1 = document.getElementById('<%= TextBox1.ClientID %>');
       var tb2 = document.getElementById('<%= TextBox2.ClientID %>');
            if( tb1.value =="" && tb2.value == "")
            {
               args.IsValid =false;
            }
            else
            {
                args.IsValid =true;
            }
     }
    </script>
<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
        <asp:TextBox ID="TextBox2" runat="server"></asp:TextBox>
        <asp:CustomValidator ID="CustomValidator1" runat="server" ErrorMessage="Enter at least one" ClientValidationFunction="checkInput"></asp:CustomValidator>
<asp:Button ID="Button1" runat="server" Text="Submit" />

hope it helps

Good Luck