validation using javascript.

<form name="myForm" action="demo_form.asp" onsubmit="return validateForm()" method="post">
First name: <input type="text" name="fname">
<input type="submit" value="Submit">
</form>

<script type="text/javascript">
function validateForm()
{
var x=document.forms["myForm"]["fname"].value;
if (x==null || x=="")
  {
  alert("First name must be filled out");
  return false;
  }
}
</script>
</head>

<asp:RequiredFieldValidator ID="RFUserName" runat="server" ControlToValidate="TxtUserName"
                                  Display="Dynamic" ForeColor="Red" ErrorMessage="Enter user name."></asp:RequiredFieldValidator>

<asp:RegularExpressionValidator ID="regexEmailValid1" runat="server"
                      ValidationExpression="\w+([-+.]\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*"
                      ControlToValidate="TxtEmailAddress" ErrorMessage="Invalid Email Format" Display="None"></asp:RegularExpressionValidator>

function IsMobileNumber(TxtMobileNo ) {
    var mob = /^[1-9]{1}[0-9]{9}$/;
    var txtMobile = document.getElementById(txtMobId);
    if (mob.test(txtMobile.value) == false) {
        alert("Please enter valid mobile number.");
        txtMobile.focus();
        return false;
    }
    return true;
}