javascript - 向上滚动时不显示导航栏
问题描述
参考这里的这个片段,我试图让我的导航在用户向上滚动时显示在顶部。向下滚动时导航可以正常消失,但向上滚动时应该会显示。
以下是片段:
<script> src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.4.1/core.js"</script>
<nav>
<div class="container">
<a href="#" id="brand">Brand</a>
<button>
<span></span>
<span></span>
<span></span>
</button>
<ul class="navbar-menu">
<li><a href="#">Home</a></li>
<li><a href="#">page a</a></li>
<li><a href="#">page b</a></li>
<li><a href="#">page c</a></li>
<li><a href="#">page d</a></li>
</ul>
</div>
</nav>
body {
background: #eee;
min-height: 3000px;
padding: 0;
margin: 0;
font-family: 'Open Sans', sans-serif;
}
.add_menu{
background: red;
}
.container {
width: 80%;
margin: 0 auto;
clear: both;
}
a {
display: inline-block;
color: #333;
text-decoration: none;
}
nav {
background: #fff;
height: 80px;
line-height: 80px;
box-shadow: 1px 1px 1px rgba(0, 0, 0, 0.2);
position: fixed;
top: 0;
left: 0;
width: 100%;
z-index: 9998;
transition: all 0.5s;
}
nav.scrollUp {
transform: translateY(-80px);
}
nav ul.navbar-menu {
margin: 0;
padding: 0;
display: inline-block;
float: right;
}
nav ul.navbar-menu li {
display: inline-block;
margin: 0 10px;
}
nav ul.navbar-menu li a {
color: #666;
font-size: 14px;
}
nav a#brand {
text-transform: uppercase;
foat: left;
font-weight: 800;
font-size: 20px;
}
nav button {
background: none;
width: 30px;
height: 40px;
margin-top: 20px;
border: none;
float: right;
display: inline-block;
cursor: pointer;
display: none;
}
nav button span {
width: 30px;
height: 40px;
height: 2px;
background: #333;
display: block;
margin: 5px 0;
}
@media (max-width: 768px) {
nav ul.navbar-menu {
display: none;
}
nav button {
display: block;
}
}
$(document).ready(function () {
var c, currentScrollTop = 0,
navbar = $('nav');
$(window).scroll(function () {
var a = $(window).scrollTop();
var b = navbar.height();
currentScrollTop = a;
if (c < currentScrollTop && a > b + b) {
navbar.addClass("scrollUp");
} else if (c > currentScrollTop && !(a <= b)) {
navbar.removeClass("scrollUp");
}
c = currentScrollTop;
});
});
当我通过检查器查看页面时,我收到一个未捕获的引用错误:
Uncaught ReferenceError: $ is not defined
但是,我已将 jquery 导入为我的片段显示。
我怎样才能解决这个问题?
解决方案
我正在编辑您已修复的某些代码部分,请检查。
$(document).ready(function () {
var c, currentScrollTop = 0,
navbar = $('nav');
$(window).scroll(function () {
var a = $(window).scrollTop();
var b = navbar.height();
currentScrollTop = a;
if (c < currentScrollTop && a > b + b) {
navbar.addClass("scrollUp");
} else if (c > currentScrollTop && !(a <= b)) {
navbar.removeClass("scrollUp");
}
c = currentScrollTop;
});
});
body {
background: #eee;
min-height: 3000px;
padding: 0;
margin: 0;
font-family: 'Open Sans', sans-serif;
}
.add_menu{
background: red;
}
.container {
width: 80%;
margin: 0 auto;
clear: both;
}
a {
display: inline-block;
color: #333;
text-decoration: none;
}
nav {
background: #fff;
height: 80px;
line-height: 80px;
box-shadow: 1px 1px 1px rgba(0, 0, 0, 0.2);
position: fixed;
top: 0;
left: 0;
width: 100%;
z-index: 9998;
transition: all 0.5s;
}
nav.scrollUp {
transform: translateY(-80px);
}
nav ul.navbar-menu {
margin: 0;
padding: 0;
display: inline-block;
float: right;
}
nav ul.navbar-menu li {
display: inline-block;
margin: 0 10px;
}
nav ul.navbar-menu li a {
color: #666;
font-size: 14px;
}
nav a#brand {
text-transform: uppercase;
foat: left;
font-weight: 800;
font-size: 20px;
}
nav button {
background: none;
width: 30px;
height: 40px;
margin-top: 20px;
border: none;
float: right;
display: inline-block;
cursor: pointer;
display: none;
}
nav button span {
width: 30px;
height: 40px;
height: 2px;
background: #333;
display: block;
margin: 5px 0;
}
@media (max-width: 768px) {
nav ul.navbar-menu {
display: none;
}
nav button {
display: block;
}
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<nav>
<div class="container">
<a href="#" id="brand">Brand</a>
<button>
<span></span>
<span></span>
<span></span>
</button>
<ul class="navbar-menu">
<li><a href="#">Home</a></li>
<li><a href="#">page a</a></li>
<li><a href="#">page b</a></li>
<li><a href="#">page c</a></li>
<li><a href="#">page d</a></li>
</ul>
</div>
</nav>
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