试图找到所选的单选按钮.怎么了？

Question

我可以读出文本字段值,但是当我尝试找到所选的单选按钮时,我什么也得不到.

$(document).ready(function(){

    $("form#create_form").submit(function() {

    var title      = $('#title').attr('value');
    var owner      = $('#owner').attr('value');
    var users      = $('#users').attr('value');
    var groups     = $('#groups').attr('value');
    var begin_date = $('#begin_date').attr('value');
    var end_date   = $('#end_date').attr('value');

    // get selected radio button 
    var type = '';
    for (i=0; i<document.forms[0].type.length; i++) {
        if (document.forms[0].type[i].checked) {
        type = document.forms[0].type[i].value;
        }
    }

HTML:

<div class="create-new">
  <form id="create_form" name="create_form" action="" method="post">
  ...
  <input name="type" id="type" value="individuel" type="radio" /> Individuel <br/>
  <input name="type" id="type" value="course"     type="radio" /> Course <br/>

  <button class="n" type="submit">Create</button>
  </form>

我究竟做错了什么？