Bootstrap 5下拉菜单响应hove自动伸展且兼容移动方案

效果：

html部份：

<nav class="navbar navbar-expand-lg navbar-dark bg-primary">
 <div class="container-fluid">
  <a class="navbar-brand" href="#">Brand</a>
  <button class="navbar-toggler" type="button" data-bs-toggle="collapse" data-bs-target="#main_nav"  aria-expanded="false" aria-label="Toggle navigation">
      <span class="navbar-toggler-icon"></span>
  </button>
  <div class="collapse navbar-collapse" id="main_nav">
    <ul class="navbar-nav">
        <li class="nav-item active"> <a class="nav-link" href="#">Home </a> </li>
        <li class="nav-item"><a class="nav-link" href="#"> About </a></li>
        <li class="nav-item"><a class="nav-link" href="#"> Services </a></li>
        <li class="nav-item dropdown">
           <a class="nav-link  dropdown-toggle" href="#" data-bs-toggle="dropdown">  Hover me  </a>
            <ul class="dropdown-menu">
              <li><a class="dropdown-item" href="#"> Submenu item 1</a></li>
              <li><a class="dropdown-item" href="#"> Submenu item 2 </a></li>
              <li><a class="dropdown-item" href="#"> Submenu item 3 </a></li>
            </ul>
        </li>
    </ul>
  </div> <!-- navbar-collapse.// -->
 </div> <!-- container-fluid.// -->
</nav>

CSS部份：

/* ============ desktop view ============ */
@media all and (min-width: 992px) {
    .navbar .nav-item .dropdown-menu{ display: none; }
    .navbar .nav-item:hover .nav-link{   }
    .navbar .nav-item:hover .dropdown-menu{ display: block; }
    .navbar .nav-item .dropdown-menu{ margin-top:0; }
}    
/* ============ desktop view .end// ============ */

JS部份(用了JS就不需要CSS）：

document.addEventListener("DOMContentLoaded", function(){
// make it as accordion for smaller screens
if (window.innerWidth > 992) {

    document.querySelectorAll('.navbar .nav-item').forEach(function(everyitem){

        everyitem.addEventListener('mouseover', function(e){

            let el_link = this.querySelector('a[data-bs-toggle]');

            if(el_link != null){
                let nextEl = el_link.nextElementSibling;
                el_link.classList.add('show');
                nextEl.classList.add('show');
            }

        });
        everyitem.addEventListener('mouseleave', function(e){
            let el_link = this.querySelector('a[data-bs-toggle]');

            if(el_link != null){
                let nextEl = el_link.nextElementSibling;
                el_link.classList.remove('show');
                nextEl.classList.remove('show');
            }


        })
    });

}
// end if innerWidth
}); 
// DOMContentLoaded  end