<div class="dropdown is-active">
  <div class="dropdown-trigger">
    <button class="button" aria-haspopup="true" aria-controls="dropdown-menu">
      <span>Dropdown button</span>
      <span class="icon is-small">
        <i class="fas 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>

import (
      . "github.com/siongui/godom"
)

func main() {
      Document.AddEventListener("DOMContentLoaded", func(e Event) {

              // Dropdowns
              dds := Document.QuerySelectorAll(".dropdown:not(.is-hoverable)")

              closeDropdowns := func() {
                      for _, dd := range dds {
                              dd.ClassList().Remove("is-active")
                      }
              }

              if len(dds) > 0 {
                      for _, dd := range dds {
                              dd.AddEventListener("click", func(e Event) {
                                      e.StopPropagation()
                                      dd.ClassList().Toggle("is-active")
                              })
                      }

                      Document.AddEventListener("click", func(e Event) {
                              closeDropdowns()
                      })
              }

              // Close dropdowns if ESC pressed
              Document.AddEventListener("keydown", func(e Event) {
                      if e.KeyCode() == 27 {
                              closeDropdowns()
                      }
              })
      })
}

'use strict';

document.addEventListener('DOMContentLoaded', function () {

  // Dropdowns

  var $dropdowns = getAll('.dropdown:not(.is-hoverable)');

  if ($dropdowns.length > 0) {
    $dropdowns.forEach(function ($el) {
      $el.addEventListener('click', function (event) {
        event.stopPropagation();
        $el.classList.toggle('is-active');
      });
    });

    document.addEventListener('click', function (event) {
      closeDropdowns();
    });
  }

  function closeDropdowns() {
    $dropdowns.forEach(function ($el) {
      $el.classList.remove('is-active');
    });
  }

  // Close dropdowns if ESC pressed
  document.addEventListener('keydown', function (event) {
    var e = event || window.event;
    if (e.keyCode === 27) {
      closeDropdowns();
    }
  });

  // Functions

  function getAll(selector) {
    return Array.prototype.slice.call(document.querySelectorAll(selector), 0);
  }
});