js怎么让移动端能下拉菜单

<div class="dropdown">
  <button class="dropbtn">下拉菜单</button>
  <div class="dropdown-content">
    <a href="#">链接1</a>
    <a href="#">链接2</a>
    <a href="#">链接3</a>
  </div>
</div>

.dropdown {
  position: relative;
  display: inline-block;
}

.dropbtn {
  background-color: #4CAF50;
  color: white;
  padding: 16px;
  font-size: 16px;
  border: none;
  cursor: pointer;
}

.dropdown-content {
  display: none;
  position: absolute;
  background-color: #f9f9f9;
  min-width: 160px;
  box-shadow: 0px 8px 16px 0px rgba(0,0,0,0.2);
  z-index: 1;
}

.dropdown-content a {
  color: black;
  padding: 12px 16px;
  text-decoration: none;
  display: block;
}

.dropdown-content a:hover {background-color: #f1f1f1}

.dropdown:hover .dropdown-content {
  display: block;
}

document.addEventListener('DOMContentLoaded', function() {
  var dropdowns = document.querySelectorAll('.dropdown');

  dropdowns.forEach(function(dropdown) {
    dropdown.addEventListener('touchstart', function(event) {
      event.stopPropagation();
      this.querySelector('.dropdown-content').style.display = 'block';
    });

    dropdown.addEventListener('touchend', function(event) {
      event.stopPropagation();
      this.querySelector('.dropdown-content').style.display = 'none';
    });
  });

  document.body.addEventListener('touchend', function() {
    dropdowns.forEach(function(dropdown) {
      dropdown.querySelector('.dropdown-content').style.display = 'none';
    });
  });
});