防止下拉菜单在单击时关闭

<div id="dropdown">
  <button onclick="toggleDropdown()">Dropdown</button>
  <div id="dropdown-content" style="display: none;">
    <a href="#">Option 1</a>
    <a href="#">Option 2</a>
    <a href="#">Option 3</a>
  </div>
</div>

#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;
}

function toggleDropdown() {
  document.getElementById("dropdown-content").classList.toggle("show");
}

window.onclick = function(event) {
  if (!event.target.matches('#dropdown button')) {
    var dropdowns = document.getElementsByClassName("dropdown-content");
    for (var i = 0; i < dropdowns.length; i++) {
      var openDropdown = dropdowns[i];
      if (openDropdown.classList.contains('show')) {
        openDropdown.classList.remove('show');
      }
    }
  }
}