此脚本为活动部分发出活动类。最近注意到它在小屏幕上停止工作。即使在chrome的开发者控制台，我将开始增加屏幕大小，它会出现，一旦我开始减少它立即停止工作(活动类消失)。但只适用于一个较长的部分，在较短的部分中，一切都有效。如何解决这个问题?
在代码片段中，我设置了一个大的固定高度，因此portfolio链接不接收活动类，在我的示例中，当section宽度增加时，它的高度减少，因此在某个时刻一切都开始工作。
const links = document.querySelectorAll('.nav-link');
const sections = [... document.querySelectorAll('.forJS')];
const callback = (entries) => {
links.forEach((link) => link.classList.remove('active'));
const elem = entries.find((entry) => entry.isIntersecting);
if (elem) {
const index = sections.findIndex((section) => section === elem.target);
links[index].classList.add('active');
}
}
let observer = new IntersectionObserver(callback, {
rootMargin: '0px',
threshold: 0.5
});
sections.forEach((section) => observer.observe(section));section {
height: 100vh;
scroll-y: auto;
}
.long{
height: 300vh;
}
.nav-link.active{
color: red;
}<script src="https://cdn.jsdelivr.net/npm/bootstrap@5.0.0-beta2/dist/js/bootstrap.min.js"></script>
<link href="https://cdn.jsdelivr.net/npm/bootstrap@5.0.0-beta2/dist/css/bootstrap.min.css" rel="stylesheet"/>
<body>
<header class="fixed-top">
<nav class="navbar navbar-expand-lg navCustom">
<div class="container">
<ul class="navbar-nav justify-content-center">
<li class="nav-item">
<a class="nav-link" href="#main">Main</a>
</li>
<li class="nav-item">
<a class="nav-link" href="#about">About us</a>
</li>
<li class="nav-item">
<a class="nav-link" href="#portfolio">Portfolio</a>
</li>
<li class="nav-item">
<a class="nav-link" href="#contacts">Contacts</a>
</li>
</ul>
</div>
</nav>
</header>
<section class="forJS text-center">Some info 1</section>
<section class="forJS text-center">Some info 2</section>
<section class="forJS text-center long">Some info 3</section>
<section class="text-center">Some info 4</section>
<section class="text-center">Some info 5</section>
<section class="text-center">Some info 6</section>
<section class="text-center">Some info 7</section>
<section class="text-center">Some info 8</section>
<section class="text-center">Some info 9</section>
<section class="forJS text-center">Some info 10</section>
</body>主要问题是threshold: 0.5。这告诉观察者一旦50%的元素在视口中可见就触发。为了你的"长久"元素，因为它的高度是300vh，而你的视口高度是100vh，所以它的最大可见性是100vh/300vh = 33%，所以观察者永远不会触发。
为了解决这个问题，你可以将阈值调整到更小的值，比如0.25。这将修复长部分的行为，但它会使较短部分的活动链接提前更改。因此，我建议您添加2个观察者:1个用于阈值为0.5 (.forJS:not(.long))的短部分，另一个用于阈值为0.25 (.forJS.long)的较长部分。
const links = document.querySelectorAll('.nav-link');
const sectionsShort = [...document.querySelectorAll('.forJS:not(.long)')];
const sectionsLong = [...document.querySelectorAll('.forJS.long')];
const sections = [...document.querySelectorAll('.forJS')];
const callback = entries => {
links.forEach((link) => link.classList.remove('active'));
const elem = entries.find((entry) => entry.isIntersecting);
if (elem) {
const index = sections.findIndex((section) => section === elem.target);
links[index].classList.add('active');
}
}
const observerShort = new IntersectionObserver(callback, {
rootMargin: '0px',
threshold: .5,
});
const observerLong = new IntersectionObserver(callback, {
rootMargin: '0px',
threshold: .25,
});
sectionsShort.forEach((section) => {
observerShort.observe(section)
});
sectionsLong.forEach((section) => {
observerLong.observe(section)
});
请像下面这样更改阈值，它会工作
const links = document.querySelectorAll('.nav-link');
const sections = [... document.querySelectorAll('.forJS')];
const callback = (entries) => {
links.forEach((link) => link.classList.remove('active'));
const elem = entries.find((entry) => entry.isIntersecting);
if (elem) {
const index = sections.findIndex((section) => section === elem.target);
links[index].classList.add('active');
}
}
let observer = new IntersectionObserver(callback, {
rootMargin: '0px',
threshold:[.5,0] // threshold changed
});
sections.forEach((section) => observer.observe(section));