下面的例子取得了该密码域所属的表单的 id - 在线编辑器

          <!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <title>蜜蜂教程(mifengjc.com)</title>
  <script>
    function displayResult() {
      var x = document.getElementById("pwd").form.id;
      alert(x);
    }
  </script>
</head>
<body>

  <form id="form1">
    密码: <input type="password" id="pwd">
  </form>
  <button type="button" onclick="displayResult()">显示所属的表单id</button>

</body>
</html>
        