Use scroll-spy to change the navbar background classes

Question

I am working on a web page in Bootstrap 4, that has sections with light and dark backgrounds and a fixed navbar. The navbar is dark (has the css class bg-dark) and, while it is easily visible against the light sections, it is indistinguishable against the dark ones.

I have added Bootstrap's scroll-spy to the page, but what it does is add the active class to the navbar items, as seen below:

.page-section {
  padding: 70px 10px
}

.page-section.bg-dark * {
  color: #fff;
}

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

<body data-spy="scroll" data-target=".navbar" data-offset="15">
  <nav class="navbar navbar-expand-sm navbar-dark bg-dark fixed-top">
    <ul class="navbar-nav">
      <li class="nav-item">
        <a class="nav-link" href="#section1">Section 1</a>
      </li>
      <li class="nav-item">
        <a class="nav-link" href="#section2">Section 2</a>
      </li>
      <li class="nav-item">
        <a class="nav-link" href="#section3">Section 3</a>
      </li>
    </ul>
  </nav>

  <div id="section1" class="container-fluid bg-light page-section">
    <h1>Section 1</h1>
    <p>Try to scroll this section and look at the navigation bar while scrolling! Try to scroll this section and look at the navigation bar while scrolling!</p>
    <p>Try to scroll this section and look at the navigation bar while scrolling! Try to scroll this section and look at the navigation bar while scrolling!</p>
  </div>
  <div id="section2" class="container-fluid bg-dark page-section">
    <h1>Section 2</h1>
    <p>Try to scroll this section and look at the navigation bar while scrolling! Try to scroll this section and look at the navigation bar while scrolling!</p>
    <p>Try to scroll this section and look at the navigation bar while scrolling! Try to scroll this section and look at the navigation bar while scrolling!</p>
  </div>
  <div id="section3" class="container-fluid bg-light page-section">
    <h1>Section 3</h1>
    <p>Try to scroll this section and look at the navigation bar while scrolling! Try to scroll this section and look at the navigation bar while scrolling!</p>
    <p>Try to scroll this section and look at the navigation bar while scrolling! Try to scroll this section and look at the navigation bar while scrolling!</p>
  </div>
</body>

How can I change the navbar's navbar-dark bg-dark to navbar-light bg-light when the user reaches div with id section3 or (even better) with class bg-light?

You may want to look at some of the options here: https://stackoverflow.com/questions/42237406/animate-shrink-navbar-on-scroll-using-bootstrap-4/42250478#42250478 — Carol Skelly, Aug 31 '18 at 15:43

score 1 · Answer 1 · answered Nov 29 '18 at 16:03

here a test with you need, but for scroll for 1 px and after begining the change for some states. sorry my bad english.

https://codepen.io/jhonycertz/pen/eQPbXy

$(window).scroll(function() {

  var isScrolled = $(document).scrollTop() > 1;
    $('.menu').toggleClass('nav_white', isScrolled);
  
$(window).on('activate.bs.scrollspy', function (e,obj) {
  if ((window.innerHeight + window.pageYOffset) >= document.body.offsetHeight) {
   return;
  }
 var Transparent = $(obj.relatedTarget).hasClass('nav_transparent');
  var White = $(obj.relatedTarget).hasClass('nav_white');
  var Blue = $(obj.relatedTarget).hasClass('nav_blue');
  $('.nav').toggleClass('nav_transparent', Transparent, !White, !Blue)
              .toggleClass('nav_white', White, !Transparent, !Blue)
              .toggleClass('nav_blue', Blue, !Transparent, !White);
});
  });

.page-section {
  padding: 70px 10px
}
.move{
  background-color:#000
}
.page-section.bg-dark * {
  color: #fff;
}
.transparent{
  background-color:green;
}
.nav_transparent{background-color:yellow;}
.nav_white{background-color:grey;}
.nav_blue{background-color:black;}

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

<body data-spy="scroll" data-target=".nav" data-offset="15">
  <nav class="menu nav navbar navbar-expand-sm nav_transparent fixed-top">
    <ul class="navbar-nav">
     <li class="nav-item ">
        <a class="nav-link" href="#section">Section 0</a>
      </li>
      <li class="nav-item d-none">
        <a class="nav-link" href="#section1">Section 1</a>
      </li>
      <li class="nav-item">
        <a class="nav-link" href="#section2">Section 2</a>
      </li>
      <li class="nav-item">
        <a class="nav-link" href="#section3">Section 3</a>
      </li>
       <li class="nav-item">
        <a class="nav-link" href="#section4">Section 4</a>
      </li>
    </ul>
  </nav>
  <div id="section" class="container-fluid bg-light page-section">
    <h1>Section 0</h1>
    <p>Try to scroll this section and look at the navigation bar while scrolling! Try to scroll this section and look at the navigation bar while scrolling!</p>
    <p>Try to scroll this section and look at the navigation bar while scrolling! Try to scroll this section and look at the navigation bar while scrolling!</p>
  </div>
  <div id="section1" class="container-fluid bg-light page-section nav_transparent">
    <h1>Section 1</h1>
    <p>Try to scroll this section and look at the navigation bar while scrolling! Try to scroll this section and look at the navigation bar while scrolling!</p>
    <p>Try to scroll this section and look at the navigation bar while scrolling! Try to scroll this section and look at the navigation bar while scrolling!</p>
  </div>
  <div id="section2" class="container-fluid bg-light page-section nav_blue">
    <h1>Section 2</h1>
    <p>Try to scroll this section and look at the navigation bar while scrolling! Try to scroll this section and look at the navigation bar while scrolling!</p>
    <p>Try to scroll this section and look at the navigation bar while scrolling! Try to scroll this section and look at the navigation bar while scrolling!</p>
  </div>
  <div id="section3" class="nav_white container-fluid bg-dark page-section">
    <h1>Section 3</h1>
    <p>Try to scroll this section and look at the navigation bar while scrolling! Try to scroll this section and look at the navigation bar while scrolling!</p>
    <p>Try to scroll this section and look at the navigation bar while scrolling! Try to scroll this section and look at the navigation bar while scrolling!</p>
  </div>
  <div id="section4" class="nav_blue container-fluid bg-light page-section">
    <h1>Section 4</h1>
    <p>Try to scroll this section and look at the navigation bar while scrolling! Try to scroll this section and look at the navigation bar while scrolling!</p>
    <p>Try to scroll this section and look at the navigation bar while scrolling! Try to scroll this section and look at the navigation bar while scrolling!</p>
  </div>
</body>

Joseph Marikle · Accepted Answer · 2018-08-31T15:05:05.577

There's no built-in way to change the target of the active class, so you're left with a javascript option. Fortunately, Bootstrap 4 does provide an event that gets triggered when a new active item is set. One odd quark with it is that the documentation suggests you can add the listener event to the element with data-spy. This does not work. You have to add it to the window object (https://stackoverflow.com/a/48694139/854246). Here's a code snippet:

$(window).on('activate.bs.scrollspy', function (e,obj) {
    // spy changes to the last item at the end of the page,
    // so we want to avoid changing the class at this point.
    // Spy still works, but we want the class to be based on
    // whatever block was closest.
    // https://stackoverflow.com/a/40370876/854246
    if ((window.innerHeight + window.pageYOffset) >= document.body.offsetHeight) {
        return;
    }

    // Here we detect the targets class.  I'm just using bg-
    // light.  Not the most robust solution, but it can be
    // tweaked.
    var isBGLight = $(obj.relatedTarget).hasClass('bg-light');
    // note that navbar needs two classes to work.  If you
    // only set bg-light/bg-dark, the link text color doesn't
    // change.
    $('.navbar').toggleClass('navbar-dark bg-dark', isBGLight)
                .toggleClass('navbar-light bg-light', !isBGLight);
});

.page-section {
  padding: 70px 10px
}

.page-section.bg-dark * {
  color: #fff;
}

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

<body data-spy="scroll" data-target=".navbar" data-offset="15">
  <nav class="navbar navbar-expand-sm navbar-dark bg-dark fixed-top">
    <ul class="navbar-nav">
      <li class="nav-item">
        <a class="nav-link" href="#section1">Section 1</a>
      </li>
      <li class="nav-item">
        <a class="nav-link" href="#section2">Section 2</a>
      </li>
      <li class="nav-item">
        <a class="nav-link" href="#section3">Section 3</a>
      </li>
    </ul>
  </nav>

  <div id="section1" class="container-fluid bg-light page-section">
    <h1>Section 1</h1>
    <p>Try to scroll this section and look at the navigation bar while scrolling! Try to scroll this section and look at the navigation bar while scrolling!</p>
    <p>Try to scroll this section and look at the navigation bar while scrolling! Try to scroll this section and look at the navigation bar while scrolling!</p>
  </div>
  <div id="section2" class="container-fluid bg-dark page-section">
    <h1>Section 2</h1>
    <p>Try to scroll this section and look at the navigation bar while scrolling! Try to scroll this section and look at the navigation bar while scrolling!</p>
    <p>Try to scroll this section and look at the navigation bar while scrolling! Try to scroll this section and look at the navigation bar while scrolling!</p>
  </div>
  <div id="section3" class="container-fluid bg-light page-section">
    <h1>Section 3</h1>
    <p>Try to scroll this section and look at the navigation bar while scrolling! Try to scroll this section and look at the navigation bar while scrolling!</p>
    <p>Try to scroll this section and look at the navigation bar while scrolling! Try to scroll this section and look at the navigation bar while scrolling!</p>
  </div>
</body>

I would make this a stack snippet, but Stack Overflow doesn't like it when you listen to events on the window object for security reasons (sandboxed iframe and whatnot), so here is a fiddle demonstrating this solution: Apparently it does support it. It just doesn't like when you use console.log

https://jsfiddle.net/jmarikle/jzg7ok0v/

Great! But what if the sections have no ids *and* the links look like this: `Contact page`? — Razvan Zamfir, Aug 31 '18 at 14:39
@RazvanZamfir You'll need a new solution then, unfortunately. [According to the documentation](https://getbootstrap.com/docs/4.0/components/scrollspy/#how-it-works), spy requires anchors that "must point to an element with [an] id." — Joseph Marikle, Aug 31 '18 at 14:41
Is that solution a 100% custom one, or is there a plugin to use? — Razvan Zamfir, Aug 31 '18 at 14:49
@RazvanZamfir It's a custom solution using what's already provided by bootstrap. jQuery is a dependency of bootstrap, so that should already be there. If you're using scroll-spy, there should be no other dependencies needed. As for, plugins, I'm not personally familiar with any that fits this particular need. Are you having trouble implementing the above code? — Joseph Marikle, Aug 31 '18 at 14:57

score 0 · Answer 3 · answered Aug 31 '18 at 15:00

Use js code for toggle class

 $(window).on('activate.bs.scrollspy', function (e,obj) 
{
   if(document.querySelector(obj.relatedTarget).classList.contains('bg-light'))
   {
      $('.navbar').removeClass("navbar-dark bg-dark");
      $('.navbar').addClass("bg-light navbar-light" );
   }
   else
   {
      $('.navbar').removeClass("bg-light navbar-light");
      $('.navbar').addClass( "navbar-dark bg-dark" );
   }
});

.page-section {
  padding: 70px 10px
}

.page-section.bg-dark * {
  color: #fff;
}

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

<body data-spy="scroll" data-target=".navbar" data-offset="15">
  <nav class="navbar navbar-expand-sm navbar-dark bg-dark fixed-top">
    <ul class="navbar-nav">
      <li class="nav-item">
        <a class="nav-link" href="#section1">Section 1</a>
      </li>
      <li class="nav-item">
        <a class="nav-link" href="#section2">Section 2</a>
      </li>
      <li class="nav-item">
        <a class="nav-link" href="#section3">Section 3</a>
      </li>
    </ul>
  </nav>

  <div id="section1" class="container-fluid bg-light page-section">
    <h1>Section 1</h1>
    <p>Try to scroll this section and look at the navigation bar while scrolling! Try to scroll this section and look at the navigation bar while scrolling!</p>
    <p>Try to scroll this section and look at the navigation bar while scrolling! Try to scroll this section and look at the navigation bar while scrolling!</p>
  </div>
  <div id="section2" class="container-fluid bg-dark page-section">
    <h1>Section 2</h1>
    <p>Try to scroll this section and look at the navigation bar while scrolling! Try to scroll this section and look at the navigation bar while scrolling!</p>
    <p>Try to scroll this section and look at the navigation bar while scrolling! Try to scroll this section and look at the navigation bar while scrolling!</p>
  </div>
  <div id="section3" class="container-fluid bg-light page-section">
    <h1>Section 3</h1>
    <p>Try to scroll this section and look at the navigation bar while scrolling! Try to scroll this section and look at the navigation bar while scrolling!</p>
    <p>Try to scroll this section and look at the navigation bar while scrolling! Try to scroll this section and look at the navigation bar while scrolling!</p>
  </div>
</body>

Use scroll-spy to change the navbar background classes

3 Answers3

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