Validate Email usign javaScript

<asp:Content ID="HeaderContent" runat="server" ContentPlaceHolderID="HeadContent">
    <script type="text/javascript">
        function myfunction(txt) {
            alert(txt);
        }
        function txtChanged(mycmt) {          
            var EmailText = document.getElementById('<%=txtemailId.ClientID%>').value;           
            alert(EmailText.length);
            if (EmailText.length == 0) {
                document.getElementById('<%=LblEmail.ClientID%>').innerHTML = 'please enter email !';
                return false;
            }
            if (validateEmail(EmailText)) {
                document.getElementById('<%=LblEmail.ClientID%>').innerHTML = 'valid Email address !';
                return true;
            }
            else {
                document.getElementById('<%=LblEmail.ClientID%>').innerHTML = 'invalid Email address !';
                return false;
            }
        }
        function validateEmail(sEmail) {
            var filter = /^([\w-\.]+)@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.)|(([\w-]+\.)+))([a-zA-Z]{2,4}|[0-9]{1,3})(\]?)$/;
            if (filter.test(sEmail)) {
                return true;
            }
            else {
                return false;
            }
        }
        //onchange="javascript: txtChanged(this);"
    </script>
</asp:Content>
<asp:Content ID="BodyContent" runat="server" ContentPlaceHolderID="MainContent">
    <asp:Button ID="Button1" runat="server" OnClientClick="myfunction('Good Morning!')"
        Text="In the Morning" />
    <asp:Label ID="LblEmail" runat="server" Text=""></asp:Label>
    <asp:TextBox ID="txtemailId" runat="server" onblur="javascript: txtChanged(this);"></asp:TextBox>
</asp:Content>