validate a Form in .Net

JavaScript Code:

<script language="javascript">

function validatefun()

{

     if (document.getElementById("<%=TextBox1.ClientID%>").value=="")

      {

                 alert("Name cannot be blank!");

                 document.getElementById("<%=TextBox1.ClientID%>").focus();

                 return false;

      }

      if(document.getElementById("<%=TextBox2.ClientID %>").value=="")

      {

                 alert("Email id cannot be blank!");

                document.getElementById("<%=TextBox2.ClientID %>").focus();

                return false;

      }

     var Email= /^([A-Za-z0-9_\-\.])+\@([A-Za-z0-9_\-\.])+\.([A-Za-z]{2,4})$/;

     var emailid=document.getElementById("<%=TextBox2.ClientID %>").value;

     var matchArr= emailid.match(Email);

     if (matchArr == null)

    {

               alert("Your email address are incorrect. So please try Again!");

               document.getElementById("<%=TextBox2.ClientID %>").focus();

               return false;

    }     

     return true;

}

</script>

HTML Code:

  Name: <asp:TextBox ID="TextBox1" runat="server" Width="100px"/>

  Email ID: <asp:TextBox ID="TextBox2" runat="server" Width="100px" 

            ToolTip="Enter Email Id" AutoPostBack="True"/>

<asp:Button ID="BtnSubmit" runat="server" Text="Submit" onclick=" BtnSubmit_Click"

                        OnClientClick="return validatefun() " />