I have built the navigation bar in my web page dynamically as shown below
NavBuilder = () => {
//to loop from section 1 to 4 and add sections to navigation
for (s = 0; s < sections.length; s++) {
const liElem = document.createElement('li');
//const divElem = document.createElement("div");
const Id = sections[s].id;
const DataNav = sections[s].dataset.nav;
liElem.innerHTML = `<a class="menu__link" href="#${Id}">${DataNav}</a>`;
Menu.appendChild(liElem);
}
}
NavBuilder();
and when I want to scroll the page I want to add a specific class "your-active-class" to the section which I created in my html page, and also add the class "active" to the liElem so whenever I scroll in the page and stop on a specific section the navbar should highlight the section I stopped on int the navbar it and also highlight the section itself.
the javaScript function I created to add the class active:
window.addEventListener('scroll', () => {
sections.forEach(s => {
const topDistance = s.getBoundingClientRect().top;
// if the distance to the top is between 0-150px
if (topDistance >= 0 && topDistance < 150) {
s.classList.add('your-active-class');
document.querySelector(`<a class="menu__link" href="#${sections[s].id}"></a>`).classList.add("active");
// otherwise, remove the class
} else {
s.classList.remove('your-active-class');
document.querySelector(`<a class="menu__link" href="#${sections[s].id}"></a>`).classList.remove("active");
}
});
});
I am still caughting this error "Uncaught TypeError: Cannot read property ‘id’ of undefined" in the line
document.querySelector(<a class="menu__link" href="#${sections[s].id}"></a>).classList.add("active");
What is the mistake i am making that prevent me from highlighting my navbar?
the html code:
<!DOCTYPE>
<html lang="en">
<head>
</head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Manipulating the DOM</title>
<!-- Load Google Fonts -->
<link href="https://fonts.googleapis.com/css?family=Fira+Sans:900|Merriweather&display=swap" rel="stylesheet">
<!-- Load Styles -->
<link href="css/styles.css" rel="stylesheet">
<body>
<!-- HTML Follows BEM naming conventions
IDs are only used for sections to connect menu achors to sections -->
<header class="page__header">
<nav class="navbar__menu">
<!-- Navigation starts as empty UL that will be populated with JS -->
<ul id="navbar__list"></ul>
</nav>
</header>
<main>
<header class="main__hero">
<h1>Landing Page </h1>
</header>
<!-- Each Section has an ID (used for the anchor) and
a data attribute that will populate the li node.
Adding more sections will automatically populate nav.
The first section is set to active class by default -->
<section id="section1" data-nav="Section 1">
<div class="landing__container">
<h2>Section 1</h2>
<p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Morbi fermentum metus faucibus lectus pharetra
dapibus. Suspendisse potenti. Aenean aliquam elementum mi, ac euismod augue. Donec eget lacinia ex. Phasellus
imperdiet porta orci eget mollis. Sed convallis sollicitudin mauris ac tincidunt. Donec bibendum, nulla eget
bibendum consectetur, sem nisi aliquam leo, ut pulvinar quam nunc eu augue. Pellentesque maximus imperdiet
elit a pharetra. Duis lectus mi, aliquam in mi quis, aliquam porttitor lacus. Morbi a tincidunt felis. Sed leo
nunc, pharetra et elementum non, faucibus vitae elit. Integer nec libero venenatis libero ultricies molestie
semper in tellus. Sed congue et odio sed euismod.</p>
<p>Aliquam a convallis justo. Vivamus venenatis, erat eget pulvinar gravida, ipsum lacus aliquet velit, vel
luctus diam ipsum a diam. Cras eu tincidunt arcu, vitae rhoncus purus. Vestibulum fermentum consectetur
porttitor. Suspendisse imperdiet porttitor tortor, eget elementum tortor mollis non.</p>
</div>
</section>
<section id="section2" data-nav="Section 2">
<div class="landing__container">
<h2>Section 2</h2>
<p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Morbi fermentum metus faucibus lectus pharetra
dapibus. Suspendisse potenti. Aenean aliquam elementum mi, ac euismod augue. Donec eget lacinia ex. Phasellus
imperdiet porta orci eget mollis. Sed convallis sollicitudin mauris ac tincidunt. Donec bibendum, nulla eget
bibendum consectetur, sem nisi aliquam leo, ut pulvinar quam nunc eu augue. Pellentesque maximus imperdiet
elit a pharetra. Duis lectus mi, aliquam in mi quis, aliquam porttitor lacus. Morbi a tincidunt felis. Sed leo
nunc, pharetra et elementum non, faucibus vitae elit. Integer nec libero venenatis libero ultricies molestie
semper in tellus. Sed congue et odio sed euismod.</p>
<p>Aliquam a convallis justo. Vivamus venenatis, erat eget pulvinar gravida, ipsum lacus aliquet velit, vel
luctus diam ipsum a diam. Cras eu tincidunt arcu, vitae rhoncus purus. Vestibulum fermentum consectetur
porttitor. Suspendisse imperdiet porttitor tortor, eget elementum tortor mollis non.</p>
</div>
</section>
</main>
<footer class="page__footer">
<p>© Udacity</p>
</footer>
<script src="js/app.js"></script>
</body>
</html>
and the active class and your-active-class
.active {
padding: 25px;
background-color: black;
color: white;
}
section.your-active-class {
background: rgb(0, 0, 0);
background: linear-gradient(0deg, rgba(211, 39, 39, 0.356) 0%, rgba(223, 10, 10, 0.548) 100%);
}
>Solution :
querySelector expects that you pass a valid CSS selector to it, which you aren’t doing. You need to change it a little bit and select by the href’s value.
In a queryselector you cannot use the <a>-syntax.
document.querySelector(`a[href="#${sections[s].id}"]`)