Bootstrap 4 - 如何使固定顶部导航栏在滚动时消失

使用 Bootstrap 4，如何使固定顶部导航栏在滚动时消失？我在下面附上了默认 Bootstrap 4 导航栏的 html 代码。

<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.1.3/css/bootstrap.min.css">

<nav class="navbar navbar-expand-md navbar-dark bg-dark fixed-top">
  <a class="navbar-brand" href="#">Test</a>
  <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarsExampleDefault" aria-controls="navbarsExampleDefault" aria-expanded="false" aria-label="Toggle navigation">
        <span class="navbar-toggler-icon"></span>
      </button>

  <div class="collapse navbar-collapse" id="navbarsExampleDefault">
    <ul class="navbar-nav ml-auto py-md-2">
      <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>
    </ul>
  </div>
</nav>

<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.3/umd/popper.min.js"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.1.3/js/bootstrap.min.js"></script>

Cue也打败了我。与他的答案类似，但不使用短代码。

jQuery

// scroll functions
$(window).scroll(function(e) {

    // add/remove class to navbar when scrolling to hide/show
    var scroll = $(window).scrollTop();
    if (scroll >= 150) {
        $('.navbar').addClass("navbar-hide");
    } else {
        $('.navbar').removeClass("navbar-hide");
    }

});

CSS 导航栏淡出选项

Codeply 演示https://www.codeply.com/go/rTR1dcn4n6 https://www.codeply.com/go/rTR1dcn4n6

.navbar {
    opacity: 1;
    transition: opacity 0.5s ease;
}

.navbar-hide {
    pointer-events: none;
    opacity: 0;
}

CSS 导航栏向上滑动选项

Codeply 演示https://www.codeply.com/go/7Fab8Thufl https://www.codeply.com/go/7Fab8Thufl

.navbar {
    transition: top 0.5s ease;
}

.navbar-hide {
    top: -56px;
}

如果您喜欢更少的代码，Cue 的答案可能会更好，下面是他使用我的隐藏类的方法。

Cue 的 jQuery

// scroll functions
$(window).scroll(function(e) {

    // add/remove class to navbar when scrolling to hide/show
    $('.navbar')[$(window).scrollTop() >= 150 ? 'addClass' : 'removeClass']('navbar-hide');

});

CSS 导航栏淡出选项（与上面相同）

Codeply 演示https://www.codeply.com/go/KPnx8ewEED https://www.codeply.com/go/KPnx8ewEED

CSS 导航栏向上滑动选项（与上面相同）

Codeply 演示https://www.codeply.com/go/i82vYBGeu7 https://www.codeply.com/go/i82vYBGeu7