C# Server Side Confirmation Popup

 Aspx Page

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

    function ShowConfirmation(){
        if (confirm(“Are you want to show the value?”) == true) {
            document.getElementById(‘<%= btnAlelrt.ClientID%>’).click();    
       }
    }

</script> 

<tr>
     <asp:Button ID=”btnDetails” runat=”server” Text=”GetValue” />
     <asp:Button ID=”btnAlelrt” runat=”server” Text=”GetDetails”/>
</tr> 

Aspx.cs file
private void CustomInitilize()
{           
            this.btnDetails.Click += new EventHandler(btnDetails_Click);
            this.btnAlelrt.Click += new EventHandler(btnAlelrt_Click);
 } 

protected void btnDetails_Click(object sender, EventArgs e)
{
     //Write your code which you wish to execute before the Confirmation from the User 
           ScriptManager.RegisterClientScriptBlock(this, typeof(Page),
           Guid.NewGuid().ToString(), “ShowConfirmation();”, true);
 }

protected void btnAlelrt_Click(object sender, EventArgs e)
{ 
     //write your code which you wish to execute after the confirmation from the user….
     Page.ClientScript.RegisterStartupScript(this.GetType(), “showVal”, “alert(‘alert2’);”, true);
}