This is the code:

<nav class="navbar navbar-expand-sm navbar-dark bg-dark">
  <div class="container">
  <a class="navbar-brand" href="#">Hello All</a>
  <button class="navbar-toggler" data-toggle="collapse"  datatarget="#navbarNav"><span class="navbar-toggler-icon"></span></button>
  <div class="collapse navbar-collapse" id="navbarNav">
  <ul class="navbar-nav ml-auto">
    <li class="nav-item">
      <a class="nav-link" href="#">Link 1</a>
    </li>
    <li class="nav-item">
      <a class="nav-link" href="#">Link 2</a>
    </li>
  </ul>
  </div>
</div>
</nav>