Dinamically Change The Action Form Attr

i have something to ask…

1. How to dynamically change the action for the form tag from username & password value that we get.. example when the value is admin, the action form will dedicated to index_admin.html.

Or

2.how to change the value of “#batas” based on username & password.. in case, on the different file.

here’s the code for index.html

<div class="collapse navbar-collapse" id="navbarNavDropdown">
            <ul class="navbar-nav">
              <li class="nav-item">
                <a class="nav-link active" aria-current="page" href="index.html">Home</a>
              </li>
              <li class="nav-item">
                <a class="nav-link" href="about.html">About Us</a>
              </li>
              <li class="nav-item">
                <a class="nav-link" href="product.html">Product</a>
              </li>
              <li class="nav-item">
                <a class="nav-link" href="contact.html">Contact Us</a>
              </li>
              <li class="nav-item">
                <a class="nav-link" href="masuk.html" id="batas">Masuk</a>
              </li>
            </ul>
          </div>

and here is the login page’s code

<form action="" id="form_id" method="post" name="myForm">
                <script>
                    document.get
                </script>
                <table>
                    <tr>
                        <td><label for="username">Username</label></td>
                        <td><input type="text" name="username" id="username" placeholder="Masukkan username" ></td>
                    </tr>
                    <tr>
                        <td><label for="password">Password</label></td>
                        <td><input type="password" name="password" id="password" placeholder="Masukkan password" ></td>
                    </tr>
                    <tr>
                        <td colspan="2"><input type="submit" value="login" id="submit" onclick="validate()"></td>
                    </tr>
                </table>
            </form>

Thank you very much for someone who asnwer this