$(document).ready(
        function(){
            if ($('#username').val() == "")
            {
                $('#username').focus();
            }
            else if ($('#pass').val() == "")
            {
                $('#pass').focus();
            }
            else
            {
                $('#b-login').focus();
            } 
            
            $('#b-login').click(
                function (event){
                    if (jQuery.trim($('#username').val()) == '')
                    {
                        $('#username').val("");
                        $('#username').focus();
                        $('#msg').html("Please, enter your username.");
                    }
                    else if (jQuery.trim($('#pass').val()) == '')
                    {
                        $('#pass').val("");
                        $('#pass').focus();
                        $('#msg').html("Please, enter your password.");
                    }
                    else
                    {
                        $('form:first').submit();
                    }
                }
            );
            
            $('#username').keyup(
                function(e) {
                    if(e.keyCode == 13) {
                        $('#b-login').focus();
                        $('#b-login').click();
                    }
                }
            );

            $('#pass').keyup(
                function(e) {
                    if(e.keyCode == 13) {
                        $('#b-login').focus();
                        $('#b-login').click();
                    }
                }
            );
        }
);