隐藏菜单javascript

I am trying to hide one of this drop down menu when the user is log-in or log-out, I use $_Session to know if the user is logged in. Something is wrong with my JavaScript. Hope anyone could help. Thanks !!Here is my code:

The two drop down menu i want to hide/show:

<li class="dropdown" id="account" >
  <a href="#" class="dropdown-toggle" data-toggle="dropdown">
    Account
    <b class="caret"></b>
  </a>
  <ul class="dropdown-menu" >
    <li><a href="#">Login</a></li>
    <li class="divider"></li>
    <li><a href="#">Register</a></li>
  </ul>

  <li class="dropdown" id="user">
    <a href="#" class="dropdown-toggle" data-toggle="dropdown">
      <?php 
        if(isset($_SESSION['username'])) {
          echo ' '.htmlentities($_SESSION['username'], ENT_QUOTES, 'UTF-8');
        }
      ?>
      <b class="caret"></b>
    </a>
    <ul class="dropdown-menu">
      <li><a href="#">Profile</a></li>
      <li><a href="#">Messages</a></li>
      <li class="divider"></li>
      <li><a href="#">Logout</a></li>
    </ul>

And here is my JavaScript code:

<script type="text/javascript">

    if (isset($_SESSION['username'])) { 
        $('#user').show();
        $('#account').hide();
    } else {
        $('#user').hide();
    }

</script>

You can use PHP to include a class on the div you want this way you might not need javascript and/or jQuery

<li class="dropdown <?php if(isset($_SESSION['username'])){echo "notvisible";} ?>" id="account" >

And use the class with CSS to set

.notvisible { display:none; }

You can also use a .toggleclass() or other means of hiding/showing menu afterward if you want.

Another way would be to echo the menu you want with PHP eg:

<?php
    if(isset($_SESSION['username'])) {
        echo "<li class=\"dropdown\" id=\"account>\"" >>> and whatever you want
    } else {
        echo "<li class=\"dropdown\" id=\"account\">" Hello user".$_SESSION['username']."And whatever else"
    }
?>