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Message: [QUOTE="MikeS, post: 4306754"] I need some validation on client side before submitting which causes a post back. I think that OnClientClick is for hooking up a client side function to a button. Return false from that function to prevent the postback. Or use the validation controls including the CustomValidator. <%@ Page Language="VB" %> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "[URL]http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd[/URL]"> <script runat="server"> Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) If IsPostBack Then Response.Write(TextBox1.Text) End If End Sub </script> <html xmlns="[URL]http://www.w3.org/1999/xhtml[/URL]" > <head runat="server"> <title>Untitled Page</title> <script> function checkIt() { var tb = document.getElementById("TextBox1"); var lbl = document.getElementById("Label1"); if (tb.value == "") { lbl.innerHTML = "Please enter something"; return false; } return true; } </script> </head> <body> <form id="form1" runat="server"> <div> <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox> <asp:Button id="Button1" runat="server" Text="Button" OnClientClick="return checkIt()"></asp:Button> <asp:Label ID="Label1" runat="server" Text=""></asp:Label> </div> </form> </body> </html> Note that using document.getElementById on server side controls is not so good as ID's for server side controls can get decorated and then their real ID is in their ClientID. So in that case you want to generate the script block server side and register it. [/QUOTE]

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