导航栏更改颜色javascript无法正常工作

Question

as other here I try to modify the navbar during scrolling down. I read this question:

Changing nav-bar color after scrolling?

Transition in Navbar when Scroll Down

Bootstrap navbar change color to the scroll

I can't make it work on my website, I don't understand the issue:

HTML:

<!-- Navbar -->
<nav class="navbar justify-content-center navbar-expand-sm navbar-dark fixed-top navbar-custom">
    <!-- Menu Links -->
    <ul class="navbar-nav" >
        <li class="nav-item">
          <a class="nav-link" href="#">Services</a>
        </li>
        <li class="nav-item">
          <a class="nav-link" href="#">Portfolio</a>
        </li>
            <!-- Wanted Logo -->
        <a class="navbar-brand" href="#">
        <img src="img/logo-light.png" alt="wanted_logo" style="width: 3vw;">
        </a>
        <li class="nav-item">
          <a class="nav-link" href="#">About us</a>
        </li>
        <li class="nav-item">
          <a class="nav-link" href="#">Contact</a>
        </li>
    </ul>
</nav>
<!-- End Navbar -->

CSS:

.navbar-custom {
    background-color: rgba(0,0,0,0.5);
}

.navbar-custom ul li{
    text-transform: uppercase;
    font-size: 14px;
    color: #fff;
    padding-top: 34px;

}

.navbar-custom img{
    margin-left: 20px;
    margin-right: 7px;
}

.navbar-custom.scrolled {
    background-color: red !important;
    transition: background-color 200ms linear;
}

JS:

<script>$(function () {
  $(document).scroll(function () {
    var $nav = $(".navbar-custom");
    $nav.toggleClass("scrolled", $(this).scrollTop() > $nav.height());
  });
});
</script>

From my understanding when scrolling down further than the size of the navbar it should change color.

I though it could be a issue because the height of the navbar is not explicitly defined here so I tried adding:

CSS

.navbar-custom{
    background-color: rgba(0,0,0,0.5);
    height: 100px;
}

It still didn't work, so I tried also to use another version of the JS proposed here: Changing nav-bar color after scrolling?

JS:

<script type="text/javascript">
    $(document).ready(function(){
      $(window).scroll(function() {
        if ($(document).scrollTop() > 100) {
          $(".navbar-custom").css("background-color", "#f8f8f8");
        } else {
          $(".navbar-custom").css("background-color", "blue");
        }
      });
    });
    </script>

Same result nothing changes.

I am new using JS what doesn't work here ?

Answer 1

It's because you're using inconsistent scrolling. You have

$(window).scroll(function() {...});

However you're checking it with

if ($(document).scrollTop() > 100) {...}

And you also have:

$(document).ready(function() {...});

Make these all either $(window) or $(document) , and it will work.

Answer 2

Finally, I made it work using this (as part of the w3 back-to-top button tutorial):

JS:

<script>
    window.onscroll = function() {scrollFunction()};

    function scrollFunction() {
        var $nav = $(".navbar-custom");

    if (document.body.scrollTop > 20 || document.documentElement.scrollTop > 50) {
        $nav.toggleClass("scrolled", $(this).scrollTop() > $nav.height());
    }
    }
</script>

Link to the w3school back to top button: https://www.w3schools.com/howto/howto_js_scroll_to_top.asp

Thank you