使用jQuery会更好:

jQuery('ul.nav li.dropdown').hover(function() {
  jQuery(this).find('.dropdown-menu').stop(true, true).show();
  jQuery(this).addClass('open');
}, function() {
  jQuery(this).find('.dropdown-menu').stop(true, true).hide();
  jQuery(this).removeClass('open');
});

这样就把上面的隐藏起来了

.navbar .dropdown-menu:before {
   display:none;
}
.navbar .dropdown-menu:after {
   display:none;
}

这个也可以。

$('.dropdown').on('mouseover',function(){
    $(this).find('.dropdown-menu').show();
});
$('.dropdown').on('mouseleave',function(){
    $(this).find('.dropdown-menu').hide();
});

如果下拉菜单在悬停元素之间有间隙，下拉菜单将立即关闭，如图所示

为了防止这种行为，您可以为事件添加一个100毫秒的超时

let dropdownTimer;
$('.dropdown').on('mouseover', () => {
    clearTimeout(dropdownTimer)
    $(this).find('.dropdown-menu').show();
});
$('.dropdown').on('mouseleave', () =>{
    dropdownTimer = setTimeout(() => {
        $(this).find('.dropdown-menu').hide();
    }, 100)
});

我希望这能有所帮助。查看链接https://jsfiddle.net/awb7gfb1/

<nav>
    <div id="menubar" class=" collapse navbar-collapse row">
        <ul id="dropdownNavbar" class="nav navbar-nav">
            <li class="dropdown">
                <button type="button" class="btn btn-primary dropbtn"><span class="glyphicon glyphicon-time"></span>
                Time Card
                <span class="caret"></span></button>
                <div class="dropdown-content">
                    <a id="showTimeCard" href="#">My Time Card</a>
                    <a href="#">Sub Menu 2</a>
                    <a href="#">Sub Menu 3</a>
                    <a href="#">Sub Menu 4</a>
                    <a href="#">Sub Menu 5</a>
                </div>
            </li>
            <li class="dropdown">
                <button type="button" class="btn btn-primary dropbtn"><span class="glyphicon glyphicon-stats"></span>
                Project
                <span class="caret"></span></button>
                <div class="dropdown-content">
                    <a href="#">Sub Menu 1</a>
                    <a href="#">Sub Menu 2</a>
                    <a href="#">Sub Menu 3</a>
                </div>
            </li>
            <li class="dropdown">
                <button type="button" class="btn btn-primary dropbtn"><span class="glyphicon glyphicon-user"></span>
                HR Links
                <span class="caret"></span></button>
                <div class="dropdown-content">
                    <a href="#">Sub Menu 1</a>
                    <a href="#">Sub Menu 2</a>
                </div>
            </li>
            <li class="dropdown">
                <button type="button" class="btn btn-primary dropbtn">
                <span class="glyphicon glyphicon-screenshot"></span>
                Leave Tracker
                <span class="caret"></span></button>
                <div class="dropdown-content">
                    <a href="#">Sub Menu 1</a>
                    <a href="#">Sub Menu 2</a>
                    <a href="#">Sub Menu 3</a>
                    <a href="#">Sub Menu 4</a>
                </div>
            </li>
            <li class="dropdown">
                <button type="button" class="btn btn-primary dropbtn">
                <span class="glyphicon glyphicon-briefcase"></span>
                Accounts
                <span class="caret"></span></button>
                <div class="dropdown-content">
                    <a href="#">Sub Menu 1</a>
                    <a href="#">Sub Menu 2</a>
                    <a href="#">Sub Menu 3</a>
                    <a href="#">Sub Menu 4</a>
                    <a href="#">Sub Menu 5</a>
                </div>
            </li>
            <li class="dropdown">
                <button type="button" class="btn btn-primary dropbtn">
                <span class="glyphicon glyphicon-headphones"></span>
                Service Desk
                <span class="caret"></span></button>
                <div class="dropdown-content">
                    <a href="#">Sub Menu 1</a>
                    <a href="#">Sub Menu 2</a>
                    <a href="#">Sub Menu 3</a>
                    <a href="#">Sub Menu 4</a>
                </div>
            </li>
            <li class="dropdown">
                <button type="button" class="btn btn-primary dropbtn">
                <span class="glyphicon glyphicon-file"></span>
                Reports
                <span class="caret"></span></button>
                <div class="dropdown-content">
                    <a href="#">Sub Menu 1</a>
                    <a href="#">Sub Menu 2</a>
                    <a href="#">Sub Menu 3</a>
                    <a href="#">Sub Menu 4</a>
                    <a href="#">Sub Menu 5</a>
                </div>
            </li>
            <li class="dropdown">
                <button type="button" class="btn btn-primary dropbtn">
                <span class="glyphicon glyphicon-cog"></span>
                Settings
                <span class="caret"></span></button>
                <div class="dropdown-content">
                    <a href="#">Sub Menu 1</a>
                    <a href="#">Sub Menu 2</a>
                    <a href="#">Sub Menu 3</a>
                </div>
            </li>
        </ul>
    </div>
</nav>

还有CSS

.dropdown {
    float: left;
    padding-right: 1px;
}

.dropbtn{
    border: 0px;
    height: 30px;
    border-radius: 0px 10px;
}
li button, .dropbtn {
    display: inline-block;
    color: white;
    text-align: center;
}

li button:hover, .dropdown:hover .dropbtn {
    background-color: #12A5F4;
}

.dropbtn.active {
    background: #12A5F4;
}

.dropdown-content {
    display: none;
    position: absolute;
    background-color: #e8f3f4;
    min-width: 100%;
    box-shadow: 0px 8px 16px 0px rgba(0, 0, 0, 0.1);
    z-index: 10;
}

.navbar-header{
    overflow: visible;
    z-index: 1;
}

.dropdown-content a {
    color: black;
    padding: 5px 10px;
    display: block;
    text-align: left;
}

.dropdown-content a:hover {
    background-color: #d8dee2
}

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

#menubar{
    padding-top: 5px;
    overflow: visible;
    z-index: 10;
    padding-left: 0px;
    padding-right: 0px;
    margin: 0px;
}

#dropdownNavbar{
    margin: 0px;
}

.navbar-toggle{
    background-color: #3382d5;
}
.navbar-toggle span{
    background-color: white;
}

使用以下代码在鼠标悬停时打开子菜单(仅适用于桌面):

$('ul.nav li.dropdown').hover(function () {
    if ($(window).width() > 767) {
        $(this).find('.dropdown-menu').show();
    }
}, function () {
    if ($(window).width() > 767) {
        $(this).find('.dropdown-menu').hide().css('display','');
    }
});

如果你想让第一关菜单是可点击的，甚至在手机上也可以添加这个:

    $('.dropdown-toggle').click(function() {
    if ($(this).next('.dropdown-menu').is(':visible')) {
        window.location = $(this).attr('href');
    }
});

子菜单(下拉菜单)将打开鼠标悬停在桌面上，点击/触摸移动和平板电脑。 一旦子菜单打开，第二次单击将让您打开链接。 多亏了if ($(window).width() > 767)，子菜单将在移动设备上采用全屏宽度。

我是这样做的:

$('ul.nav li.dropdown').hover(function(){
       $(this).children('ul.dropdown-menu').slideDown(); 
    }, function(){
       $(this).children('ul.dropdown-menu').slideUp(); 
});

我希望这能帮助到一些人……