I have made client side validation in ASP .NET and if validation success then run server side code

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C#

ASP

Javascript

in asp .Net I have button control on client click event I have Performed client side validation and on button click I am inserting data into database but In my case even
if client side validation function

return false;

. then also it is Executing Server Code.

What I have tried:

I have Asp .net

ImageButton

as follows

<asp:ImageButton ID="ImgSave" runat="server" ImageUrl="~/images/save.gif" TabIndex="11" OnClientClick="Validate();" ToolTip="Save" Visible="true" OnClick="ImgSave_Click" />

javascript function is as

function Validate()//
{
    if (document.getElementById('DrpTitle').selectedIndex == 0)//
    {
        var msg = "Please Select Title";
        document.getElementById('lblMessage').innerHTML = msg;
        document.getElementById('divForBasic').style.display = 'block';
        document.getElementById('divForContact').style.display = 'none';
        document.getElementById('divForAddress').style.display = 'none';
        document.getElementById('divForIdent').style.display = 'none';
        document.getElementById('divForBank').style.display = 'none';
        document.getElementById('divForWork').style.display = 'none';
        document.getElementById('divForEducation').style.display = 'none';
        document.getElementById('divForPersonal').style.display = 'none';
        document.getElementById('divForSocial').style.display = 'none';
        document.getElementById('DrpTitle').focus();

        return false;
    }
    if (document.getElementById('TxtFName').value == '') //
    {
        if (document.getElementById('TxtFName').value.length < 1)//
        {
            var msg = "Please Enter First Name";
            document.getElementById('lblMessage').innerHTML = msg;
            document.getElementById('divForBasic').style.display = 'block';
            document.getElementById('divForContact').style.display = 'none';
            document.getElementById('divForAddress').style.display = 'none';
            document.getElementById('divForIdent').style.display = 'none';
            document.getElementById('divForBank').style.display = 'none';
            document.getElementById('divForWork').style.display = 'none';
            document.getElementById('divForEducation').style.display = 'none';
            document.getElementById('divForPersonal').style.display = 'none';
            document.getElementById('divForSocial').style.display = 'none';
            document.getElementById('TxtFName').focus();

            return false;
        }
    }