<!DOCTYPE html><html><head><meta charset="utf-8"></head><body>

<!-- Simplest form with username and password fields. -->
  <input id="form-basic-username" name="username">
  <input id="form-basic-password" name="password" type="password">
  <input id="form-basic-submit" type="submit">

  <button id="add">Add input[type=password]</button>

  <script>
    document.getElementById("add").addEventListener("click", function() {
      var node = document.createElement("input");
      node.setAttribute("type", "password");
      document.querySelector("body").appendChild(node);
    });
  </script>

</body></html>
