Keeping Model Opened With Incomplete Form

http://stackoverflow.com/questions/25540705/form-submit-in-popup-box/25541099#25541099

HTML

<script src="http://leanmodal.finelysliced.com.au/js/jquery.leanModal.min.js"></script>
<div id="w">
    <div id="content">
        <center><a href="#loginmodal" class="flatbtn" id="modaltrigger">Modal Login</a>

        </center>
    </div>
</div>
<div id="loginmodal" style="display:none;">
     <h1>User Login</h1>

    <form id="loginform" method="post" action="/echo/json/">
        <label for="username">Username:</label>
        <input type="text" name="username" id="username" class="txtfield" tabindex="1" />
        <label for="password">Password:</label>
        <input type="password" name="password" id="password" class="txtfield" tabindex="2" />
        <div class="center">
            <input type="submit" name="loginbtn" id="loginbtn" class="flatbtn-blu hidemodal" value="Log In" tabindex="3" />
        </div>
    </form>
</div>

JavaScript

(function ($) {
    $('#loginform').submit(function (e) {
        if (!$('#username').val()) {
            $('#loginmodal').show();
        } else console.log("Enter your username");
        return false;
    });

    $('#modaltrigger').leanModal({
        top: 110,
        overlay: 0.45,
        closeButton: ".hidemodal"
    });
})(jQuery);