问Bulma下拉菜单不工作

EN

var dropdown = document.querySelector('.dropdown');
dropdown.addEventListener('click', function(event) {
  event.stopPropagation();
  dropdown.classList.toggle('is-active');
});

<link href="https://cdnjs.cloudflare.com/ajax/libs/bulma/0.6.0/css/bulma.min.css" rel="stylesheet" />
<link rel="stylesheet" href="https://use.fontawesome.com/releases/v5.5.0/css/all.css" integrity="sha384-B4dIYHKNBt8Bc12p+WXckhzcICo0wtJAoU8YZTY5qE0Id1GSseTk6S+L3BlXeVIU" crossorigin="anonymous">


<div class="dropdown">
  <div class="dropdown-trigger">
    <button class="button" aria-haspopup="true" aria-controls="dropdown-menu">
      <span>Dropdown button</span>
      <span class="icon is-small">
        <!--fontawesome required for the icon-->
        <i class="fa fa-angle-down" aria-hidden="true"></i>
      </span>
    </button>
  </div>
  <div class="dropdown-menu" id="dropdown-menu" role="menu">
    <div class="dropdown-content">
      <a href="#" class="dropdown-item">
        Dropdown item
      </a>
      <a class="dropdown-item">
        Other dropdown item
      </a>
      <a href="#" class="dropdown-item is-active">
        Active dropdown item
      </a>
      <a href="#" class="dropdown-item">
        Other dropdown item
      </a>
      <hr class="dropdown-divider">
      <a href="#" class="dropdown-item">
        With a divider
      </a>
    </div>
  </div>
</div>