Bootstrap 4: Multilevel Dropdown Inside Navigation

The following is MultiLevel dropdown based on bootstrap4. I tried it was according to the bootstrap4 basic dropdown.

.dropdown-submenu{
    position: relative;
}
.dropdown-submenu a::after{
    transform: rotate(-90deg);
    position: absolute;
    right: 3px;
    top: 40%;
}
.dropdown-submenu:hover .dropdown-menu, .dropdown-submenu:focus .dropdown-menu{
    display: flex;
    flex-direction: column;
    position: absolute !important;
    margin-top: -30px;
    left: 100%;
}
@media (max-width: 992px) {
    .dropdown-menu{
        width: 50%;
    }
    .dropdown-menu .dropdown-submenu{
        width: auto;
    }
}
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-alpha.6/css/bootstrap.min.css" integrity="sha384-rwoIResjU2yc3z8GV/NPeZWAv56rSmLldC3R/AZzGRnGxQQKnKkoFVhFQhNUwEyJ" crossorigin="anonymous">
<script src="https://code.jquery.com/jquery-3.1.1.slim.min.js" integrity="sha384-A7FZj7v+d/sdmMqp/nOQwliLvUsJfDHW+k9Omg/a/EheAdgtzNs3hpfag6Ed950n" crossorigin="anonymous"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/tether/1.4.0/js/tether.min.js" integrity="sha384-DztdAPBWPRXSA/3eYEEUWrWCy7G5KFbe8fFjk5JAIxUYHKkDx6Qin1DkWx51bBrb" crossorigin="anonymous"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-alpha.6/js/bootstrap.min.js" integrity="sha384-vBWWzlZJ8ea9aCX4pEW3rVHjgjt7zpkNpZk+02D9phzyeVkE+jo0ieGizqPLForn" crossorigin="anonymous"></script>

<nav class="navbar navbar-toggleable-md navbar-light bg-faded">
  <button class="navbar-toggler navbar-toggler-right" type="button" data-toggle="collapse" data-target="#navbarNavDropdown" aria-controls="navbarNavDropdown" aria-expanded="false" aria-label="Toggle navigation">
    <span class="navbar-toggler-icon"></span>
  </button>
  <a class="navbar-brand" href="#">Navbar</a>
  <div class="collapse navbar-collapse" id="navbarNavDropdown">
    <ul class="navbar-nav mr-auto">
      <li class="nav-item active">
        <a class="nav-link" href="#">Home <span class="sr-only">(current)</span></a>
      </li>
      <li class="nav-item">
        <a class="nav-link" href="#">Link 1</a>
      </li>
      <li class="nav-item dropdown">
        <a class="nav-link dropdown-toggle" href="http://example.com" id="navbarDropdownMenuLink" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
          Dropdown link
        </a>
        <ul class="dropdown-menu" aria-labelledby="navbarDropdownMenuLink">
          <li><a class="dropdown-item" href="#">Action</a></li>
          <li><a class="dropdown-item" href="#">Another action</a></li>
          <li class="dropdown-submenu"><a class="dropdown-item dropdown-toggle" data-toggle="dropdown" href="#">Something else here</a>
            <ul class="dropdown-menu">
              <a class="dropdown-item" href="#">A</a>
              <a class="dropdown-item" href="#">b</a>
            </ul>
          </li>
        </ul>
      </li>
    </ul>
  </div>
</nav>

I use the following piece of CSS and JavaScript. It uses an extra class dropdown-submenu. I tested it with Bootstrap 4 beta.

It supports multi level sub menus.

$('.dropdown-menu a.dropdown-toggle').on('click', function(e) {
  if (!$(this).next().hasClass('show')) {
    $(this).parents('.dropdown-menu').first().find('.show').removeClass('show');
  }
  var $subMenu = $(this).next('.dropdown-menu');
  $subMenu.toggleClass('show');


  $(this).parents('li.nav-item.dropdown.show').on('hidden.bs.dropdown', function(e) {
    $('.dropdown-submenu .show').removeClass('show');
  });


  return false;
});
.dropdown-submenu {
  position: relative;
}

.dropdown-submenu a::after {
  transform: rotate(-90deg);
  position: absolute;
  right: 6px;
  top: .8em;
}

.dropdown-submenu .dropdown-menu {
  top: 0;
  left: 100%;
  margin-left: .1rem;
  margin-right: .1rem;
}
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-beta/css/bootstrap.min.css" integrity="sha384-/Y6pD6FV/Vv2HJnA6t+vslU6fwYXjCFtcEpHbNJ0lyAFsXTsjBbfaDjzALeQsN6M" crossorigin="anonymous">

<script src="https://code.jquery.com/jquery-3.2.1.slim.min.js" integrity="sha384-KJ3o2DKtIkvYIK3UENzmM7KCkRr/rE9/Qpg6aAZGJwFDMVNA/GpGFF93hXpG5KkN" crossorigin="anonymous"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.11.0/umd/popper.min.js" integrity="sha384-b/U6ypiBEHpOf/4+1nzFpr53nxSS+GLCkfwBdFNTxtclqqenISfwAzpKaMNFNmj4" crossorigin="anonymous"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-beta/js/bootstrap.min.js" integrity="sha384-h0AbiXch4ZDo7tp9hKZ4TsHbi047NrKGLO3SEJAg45jXxnGIfYzk4Si90RDIqNm1" crossorigin="anonymous"></script>

<nav class="navbar navbar-expand-lg navbar-light bg-light">
  <a class="navbar-brand" href="#">Navbar</a>
  <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarNavDropdown" aria-controls="navbarNavDropdown" aria-expanded="false" aria-label="Toggle navigation">
    <span class="navbar-toggler-icon"></span>
  </button>
  <div class="collapse navbar-collapse" id="navbarNavDropdown">
    <ul class="navbar-nav">
      <li class="nav-item active">
        <a class="nav-link" href="#">Home <span class="sr-only">(current)</span></a>
      </li>
      <li class="nav-item dropdown">
        <a class="nav-link dropdown-toggle" href="http://example.com" id="navbarDropdownMenuLink" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
          Dropdown link
        </a>
        <ul class="dropdown-menu" aria-labelledby="navbarDropdownMenuLink">
          <li><a class="dropdown-item" href="#">Action</a></li>
          <li><a class="dropdown-item" href="#">Another action</a></li>
          <li class="dropdown-submenu">
            <a class="dropdown-item dropdown-toggle" href="#">Submenu</a>
            <ul class="dropdown-menu">
              <li><a class="dropdown-item" href="#">Submenu action</a></li>
              <li><a class="dropdown-item" href="#">Another submenu action</a></li>


              <li class="dropdown-submenu">
                <a class="dropdown-item dropdown-toggle" href="#">Subsubmenu</a>
                <ul class="dropdown-menu">
                  <li><a class="dropdown-item" href="#">Subsubmenu action</a></li>
                  <li><a class="dropdown-item" href="#">Another subsubmenu action</a></li>
                </ul>
              </li>
              <li class="dropdown-submenu">
                <a class="dropdown-item dropdown-toggle" href="#">Second subsubmenu</a>
                <ul class="dropdown-menu">
                  <li><a class="dropdown-item" href="#">Subsubmenu action</a></li>
                  <li><a class="dropdown-item" href="#">Another subsubmenu action</a></li>
                </ul>
              </li>



            </ul>
          </li>
        </ul>
      </li>
    </ul>
  </div>
</nav>

Updated 2018

Here is another variation on the Bootstrap 4.1 Navbar with multi-level dropdown. This one uses minimal CSS for the submenu, and can be re-positioned as desired:

enter image description here

https://codeply.com/go/nG6iMAmI2X

.dropdown-submenu {
  position: relative;
}

.dropdown-submenu .dropdown-menu {
  top: 0;
  left: 100%;
  margin-top: -1px;
}

jQuery to control display of submenus:

$('.dropdown-submenu > a').on("click", function(e) {
    var submenu = $(this);
    $('.dropdown-submenu .dropdown-menu').removeClass('show');
    submenu.next('.dropdown-menu').addClass('show');
    e.stopPropagation();
});

$('.dropdown').on("hidden.bs.dropdown", function() {
    // hide any open menus when parent closes
    $('.dropdown-menu.show').removeClass('show');
});

See this answer for activating the Bootstrap 4 submenus on hover