未捕获的TypeError：提交表单时无法读取未定义的属性“ element”

我有一个使用PHP的HTML div输出，单击“提交”时，它应该提交表单并触发JS函数。提交后，Chrome中的JS控制台给我以下错误：

未捕获的TypeError：无法读取未定义的属性“ element”

我的HTML（用PHP heredoc包装）

<div id="tab5" class="tab">
     <div id="reopen_case_form">
        This Case has been previously closed by Workbooks Support. You can re-open this ticket at any time by providing a reason why you'd like to do so and clicking "Re-open Case".
        <table class="update_case">
         <tr><td style="padding: 10px">Summary:<input id="name" name="name" type="text" size="80" maxlength="255" class="required"/></td></tr>
         <tr><td><textarea id="description" name="description" cols="255" rows="50"></textarea></td></tr>
         <tr>
          <td colspan="2" style="padding-top: 10px;">
            <input type="file" class="file" name="file1" id="file1" style="display: inline">
            <input type="file" class="file" name="file2" id="file2" style="display: inline">
            <input type="file" class="file" name="file3" id="file3" style="display: inline">
          </td></tr>
      </table>
      <p><button type="submit" onclick="on_reopen_case()" style="float:left; margin-top: 10px; margin-bottom: 10px;" value="reopen_case" id="reopen_case" name="reopen_case" class="quietbutton">Re-open Case</button></p>
    </div>
  </div>

我的Javascript：

<script type="text/javascript">
    function on_reopen_case() {
      if (!$("#reopen_case_form").valid()){ return false; }
      $('#reopen_case').attr('disabled', 'disabled');
      $('#reopen_case').text('Re-opening case. Please wait...');
      document.body.style.cursor = "progress";
      $("#function").val("reopen_case");
      fade();
      $("#reopen_case_form").submit();
    };
  </script>

表单似乎已提交，但没有将按钮文本更改为“重新打开案例”，也没有将#function设置为指定值。

烦人的是，我在其他地方使用了类似的方法，并且可行：

<div id="tab3" class="tab">
     <div id="update_case_form">
        Provide a summary and detailed description of your update below, including screenshots where applicable. Click "Update Case" to submit your update to the Workbooks Support team.
      <table class="update_case">
         <tr><td style="padding: 10px">Summary:<input id="name" name="name" type="text" size="80" maxlength="255" class="required"/></td></tr>
         <tr><td><textarea id="description" name="description" cols="255" rows="50"></textarea></td></tr>
         <tr>
          <td colspan="2" style="padding-top: 10px;">
            <input type="file" class="file" name="file1" id="file1" style="display: inline">
            <input type="file" class="file" name="file2" id="file2" style="display: inline">
            <input type="file" class="file" name="file3" id="file3" style="display: inline">
          </td></tr>
      </table>
      <p><button type="submit" onclick="on_create_activity()" style="float:left; margin-top: 10px; margin-bottom: 10px;" value="create_activity" id="create_activity" name="create_activity" class="quietbutton">Update Case</button></p>
     </div>
  </div>

Java脚本

 <script type="text/javascript">
    function on_create_activity() {
      if (!$("#update_case_form").valid()){ return false; }
      $('#create_activity').attr('disabled', 'disabled');
      $('#create_activity').text('Updating case. Please wait...');
      document.body.style.cursor = "progress";
      $("#function").val("create_activity");
      fade();
      $("#update_case_form").submit();
    };
  </script>

我无法弄清楚我要去哪里了！帮助....