如何使我的导航栏从无阴影变为阴影，并在滚动条上进行淡入淡出过渡？

Question

我希望我的导航栏在滚动时从无阴影变为阴影 — 完成（阅读下面我的回答）。现在我想为滚动上的阴影添加淡入淡出过渡效果。阅读下面的“更新”。

$(document).ready(function() {
        // Transition effect for navbar
        $(window).scroll(function() {
          // checks if window is scrolled more than 500px, adds/removes solid class
          if($(this).scrollTop() > 500) {
              $('.topnav').addClass('shadow');
          } else {
              $('.topnav').removeClass('shadow');
          }
        });
});

.logo {
    float: left;
  padding-left: 20px;
    padding-right: 15px;
    padding-bottom: 30px;
    padding-top: 20px;
    width: 210px;
    height: auto;
}

.topnav {
  overflow: hidden;
  background-color: white;
    top: 0;
  left: 0;
    margin: 0;
  padding: 0;
    z-index: 1000;
  width: 100%; !important;
    position: fixed;
}

.topnav.shadow {
  -webkit-box-shadow: 0px 0px 9px 3px rgba(41,41,41,.25);
  -moz-box-shadow: 0px 0px 9px 3px rgba(41,41,41,.25);
  box-shadow: 0px 0px 9px 3px rgba(41,41,41,.25);
}

.topnav a {
  float: left;
    display: block;
    color: grey;
    text-align: center;
    padding-top: 30px;
    padding-bottom: 0px;
    padding-left: 16px;
    padding-right: 16px;
    text-decoration: none;
    font-size: 18px;
    transition: color 0.3s ease-out;
}

.active, .nav-btn {
  color: #1a1a1a;
}

@media (max-width: 800px) {
    .resp-t-n {
        padding-top: 60px;
    }
    .resp-b-n {
        padding-bottom: 30px;
    }
    .logo {
        width: 130px;
        height: auto;
    }
}


.topnav .icon {
  display: none;
}

.dropdown {
    float: left;
    overflow: hidden;
}

.dropdown .dropbtn {
    font-size: 17px;
    border: none;
  outline: none;
    color: grey;
    padding: 34px 16px;
    background-color: inherit;
    font-family: inherit;
    margin: 0;
    transition: color 0.3s ease-out;
}

.dropdown-content {
    display: none;
    position: fixed;
    background-color: #f9f9f9;
    min-width: 160px;
    box-shadow: 0px 8px 16px 0px rgba(0,0,0,0.2);
    z-index: 1001;
}

.dropdown-content a {
    float: none;
    color: grey;
    padding: 12px 16px;
    text-decoration: none;
    display: block;
    text-align: left;
}

.topnav a:hover:not(.logo), .dropdown:hover .dropbtn {
    color: #1a1a1a;
    transition: color 0.5s ease;
}

.dropdown-content a:hover {
    background-color: #ddd;
    color: black;
}

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

@media screen and (max-width: 800px) {
  .topnav a:not(:first-child), .dropdown .dropbtn .resp-t-n .resp-b-n {
    display: none;
  }
  .topnav a.icon {
    float: right;
    display: block;
  }
}

@media screen and (max-width: 800px) {
  .topnav.responsive {
      position: fixed;
  }
  .topnav.responsive .icon {
    position: fixed;
    right: 0;
    top: 0;
  }
  .topnav.responsive a {
    float: none;
    display: block;
    text-align: left;
  }
  .topnav.responsive .dropdown {float: none;}
  .topnav.responsive .dropdown-content {position: relative;}
  .topnav.responsive .dropdown .dropbtn {
    display: block;
    width: 100%;
    text-align: left;
  }
}

#active {
  color: #1a1a1a;
}

 <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.5.1/jquery.min.js"></script>
 
 <div class="topnav" id="myTopnav">
    <img class="logo" src="[img path]">
        <a href="/" id="active"><div class="resp-t-n">Home</div></a>
        <a href="elements.html">Elements</a>
        <a href="about.html">About</a>
        <a href="contact.html"><div class="resp-b-n">Contact</div></a>
    <a href="javascript:void(0);" style="font-size:15px;" class="icon" onclick="myFunction()"><i class="fal fa-bars"></i></a>
  </div>

我正在尝试学习如何从头开始编写代码以及任何我不知道的东西，我通常只是搜索，但我真的找不到有效的解决方案，因此我的第一个 post .

非常感谢任何帮助:)

~~在我的控制台中发现一个错误：~~

~~未捕获的引用错误：$ 未定义在 main.js:14~~

~~第14行的代码是 $(document).ready(function() {~~ — 我解决了这个问题

已更新

我现在想为滚动上的阴影添加淡入淡出过渡。 CSS 可以实现还是必须使用 JS 进行备份？

Answer 1

$(document).ready(function() {
  // Transition effect for navbar
  $(window).scroll(function() {
    // checks if window is scrolled more than 500px, adds/removes solid class
    if ($(this).scrollTop() > 50) {
      $('.topnav').addClass('shadow');
    } else {
      $('.topnav').removeClass('shadow');
    }
  });
});

body {
  height: 200vh/* just for checking purpose */
}

.logo {
  float: left;
  padding-left: 20px;
  padding-right: 15px;
  padding-bottom: 30px;
  padding-top: 20px;
  width: 210px;
  height: auto;
}

.topnav {
  overflow: hidden;
  background-color: white;
  top: 0;
  left: 0;
  margin: 0;
  padding: 0;
  z-index: 1000;
  width: 100%;
  position: fixed;
}

.topnav.shadow {
  -webkit-box-shadow: 0px 0px 9px 3px rgba(41, 41, 41, .25);
  -moz-box-shadow: 0px 0px 9px 3px rgba(41, 41, 41, .25);
  box-shadow: 0px 0px 9px 3px rgba(41, 41, 41, .25);
}

.topnav a {
  float: left;
  display: block;
  color: grey;
  text-align: center;
  padding-top: 30px;
  padding-bottom: 0px;
  padding-left: 16px;
  padding-right: 16px;
  text-decoration: none;
  font-size: 18px;
  transition: color 0.3s ease-out;
}

.active,
.nav-btn {
  color: #1a1a1a;
}

@media (max-width: 800px) {
  .resp-t-n {
    padding-top: 60px;
  }
  .resp-b-n {
    padding-bottom: 30px;
  }
  .logo {
    width: 130px;
    height: auto;
  }
}

.topnav .icon {
  display: none;
}

.dropdown {
  float: left;
  overflow: hidden;
}

.dropdown .dropbtn {
  font-size: 17px;
  border: none;
  outline: none;
  color: grey;
  padding: 34px 16px;
  background-color: inherit;
  font-family: inherit;
  margin: 0;
  transition: color 0.3s ease-out;
}

.dropdown-content {
  display: none;
  position: fixed;
  background-color: #f9f9f9;
  min-width: 160px;
  box-shadow: 0px 8px 16px 0px rgba(0, 0, 0, 0.2);
  z-index: 1001;
}

.dropdown-content a {
  float: none;
  color: grey;
  padding: 12px 16px;
  text-decoration: none;
  display: block;
  text-align: left;
}

.topnav a:hover:not(.logo),
.dropdown:hover .dropbtn {
  color: #1a1a1a;
  transition: color 0.5s ease;
}

.dropdown-content a:hover {
  background-color: #ddd;
  color: black;
}

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

@media screen and (max-width: 800px) {
  .topnav a:not(:first-child),
  .dropdown .dropbtn .resp-t-n .resp-b-n {
    display: none;
  }
  .topnav a.icon {
    float: right;
    display: block;
  }
}

@media screen and (max-width: 800px) {
  .topnav.responsive {
    position: fixed;
  }
  .topnav.responsive .icon {
    position: fixed;
    right: 0;
    top: 0;
  }
  .topnav.responsive a {
    float: none;
    display: block;
    text-align: left;
  }
  .topnav.responsive .dropdown {
    float: none;
  }
  .topnav.responsive .dropdown-content {
    position: relative;
  }
  .topnav.responsive .dropdown .dropbtn {
    display: block;
    width: 100%;
    text-align: left;
  }
}

#active {
  color: #1a1a1a;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.5.1/jquery.min.js"></script>

<div class="topnav" id="myTopnav">
  <img class="logo" src="[img path]">
  <a href="/" id="active">
    <div class="resp-t-n">Home</div>
  </a>
  <a href="elements.html">Elements</a>
  <a href="about.html">About</a>
  <a href="contact.html">
    <div class="resp-b-n">Contact</div>
  </a>
  <a href="javascript:void(0);" style="font-size:15px;" class="icon" onclick="myFunction()"><i class="fal fa-bars"></i></a>
</div>

您的页面 window 内容较少。如果您的 js 中提到的内容超过 500px，它会起作用。

Answer 2

问题是 <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.5.1/jquery.min.js"></script> 在我的主 .js 文件下面。我只是把它移到上面。这么简单又愚蠢的错误！

对于我问题的第二部分——过渡——我添加了 transition: 1s; 到 .topnav

非常感谢大家的宝贵时间:)

如何使我的导航栏从无阴影变为阴影，并在滚动条上进行淡入淡出过渡？

How do I make my navbar go from no shadow to shadow with fade transition on scroll?

html

javascript

css

navigation