下面的例子可获得密码域的默认 - 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").value;
      alert(x);
    }
  </script>
</head>
<body>

  <form>
    密码: <input type="password" id="pwd">
  </form>
  <button type="button" onclick="displayResult()">显示值</button>

</body>
</html>
        