问Jquery空字段在字段旁添加消息

EN

    $(document).ready(function(){
    $("#login_form").submit(function(event){
    var username = $.trim($("#username").val());
    var password = $.trim($("#password").val());


    if(username.length < 1){
            if(!$("#user_error").length){
            $("#username_error").append("<p id='user_error'>Required</p>");
            }
    }

    if(username.length < 1|| password.length < 1){ 
    $("#username_error").append("<p id='user_error'>Required</p>");
    $("#password_error").append("<p id='pass_error'>Required</p>");
    event.preventDefault();
    }




    });
});

<? $attr = array( "id" => "login_form"); echo form_open("KGLogin/verify_login",$attr); ?>
        <table id="loginform">
        <tr>
        <th>Log-in</th>
        </tr>
        <tr>
        <td>
        <input type="text" name="username" id='username' placeholder="Username" />
        </td>
        <td id="username_error"></td>
        </tr>
        <tr>
        <td>
        <input type="password" name="password" id='password' placeholder="Password" />
        </td>
        <td id="password_error"></td>
        </tr>
        <tr>
        <td>
        <input type="submit" name="login" value="Login" />
        </td>
        </tr>
        </table>
        <? echo form_close(); ?>