Hi,
Its seems like that you are going to implement js valiadtion on your form using jQuery. To achive goal we follows few steps such as
<%@ Page Title="Home Page" Language="C#" MasterPageFile="~/Site.master" AutoEventWireup="true"
CodeBehind="Default.aspx.cs" Inherits="TestDemo._Default" %>
<asp:Content ID="HeaderContent" runat="server" ContentPlaceHolderID="HeadContent">
<script type="text/javascript" src="http://code.jquery.com/jquery-1.11.1.min.js"></script>
<asp:Content ID="BodyContent" runat="server" ContentPlaceHolderID="MainContent">
<asp:TextBox ID="txtOperation" runat="server">
<asp:Button ID="btnSave" runat="server" Text="Save" OnClientClick="return save()" />
<script type="text/javascript">
function save() {
var operationValue = $("#<%=txtOperation.ClientID %>").val();
if (operationValue.trim() == '') {
alert("operation value is empty");
return false;
}
return true;
}
</script>