jQuery 获取 ajax POST 的表单值

我试图通过AJAX将表单值发布到php文件中.如何收集表单值以发送到"data"参数内部？

$.ajax({
        type: "POST",
        data: "submit=1&username="+username+"&email="+email+"&password="+password+"&passconf="+passconf,
        url: "http://rt.ja.com/includes/register.php",
        success: function(data)
        {   
            //alert(data);
            $('#userError').html(data);
            $("#userError").html(userChar);
            $("#userError").html(userTaken);
        }
    });

HTML:

<div id="border">
  <form  action="/" id="registerSubmit">
    <div id="userError"></div>
      Username: <input type="text" name="username" id="username" size="10"/><br>
      <div id="emailError" ></div>
      Email: <input type="text" name="email" size="10" id="email"/><br>
      <div id="passError" ></div>
      Password: <input type="password" name="password" size="10" id="password"/><br>
      <div id="passConfError" ></div>
      Confirm Password: <input type="password" name="passconf" size="10" id="passconf"/><br>
      <input type="submit" name="submit" value="Register" />
  </form>
</div>