聚合铁表单-禁用提交?

我正在使用 iron-form 我正在努力 POST 将文件发送到(当前为本地)服务器。我有两个按钮,一个用于发送文件,另一个用于取消。我在取消时遇到问题。以下是表格:

<form  is="iron-form" action="http://localhost:7733/receivedoc" id="restForm" method="post" >
  <table class="starter-inputs">
    <tr><td>
    <px-file-upload 
      id="uploadComponentId"
      message="Drag and drop files here, or click the button below." 
      multiple=false 
      accept=".xls,.xlsx">
    </px-file-upload>
    </td></tr>
    </table>
    <button class="btn btn--large btn--icon" id="saveDataSetButton">
      <i class="fa-briefcase">Generate Pacing File</i>
    </button>
    <button class="btn btn--large btn--icon" id="cancelDataSetButton">
      <i class="fa-briefcase">Cancel</i>
    </button>
    <div class="output"></div>
  </form>

这个 cancelDataSetButton 被处理为:

this.$.cancelDataSetButton.addEventListener('click', function() {
  console.log('restForm.cancelDataSetButton click')
  restForm.reset();
  restForm.querySelector('.output').innerHTML = 'Operation cancelled.';
});

然而,自 By default, a native element (or input type="submit") will submit this form. 这个 邮递 无论如何都会被激发。如何防止“取消”按钮 邮递 ing?