使用原版 javascript 在元素位于视口中时突出显示导航栏列表？

Question

当我滚动到正文中的特定部分时，我想更改导航栏中列表元素的背景 JavaScript...我已经创建了一个检查 ViewPort 的函数，但我很难为集合中的每个 HTML 元素放置监听器。有人可以帮忙吗？

/* VARIABLES */
const newSectionBtn = document.getElementById("new-section");
const main = document.getElementById("main");
const backBtn = document.getElementById("back");
let allLists = document.getElementsByTagName("li");
let allSections = document.getElementsByTagName("section");
let n = 4;

/* FUNCTIONS */
function duplicate(num) {
  const newSection = document.createElement("section");
  const newDiv = document.createElement("div");
  const heading = document.createElement("h2");
  const p1 = document.createElement("p");
  const p2 = document.createElement("p");

  newSection.appendChild(newDiv);
  newDiv.appendChild(heading);
  newDiv.appendChild(p1);
  newDiv.appendChild(p2);

  newSection.setAttribute("id", "section" + num);
  newSection.setAttribute("data-nav", "Section" + " " + num);
  newDiv.setAttribute("class", "landing__container");

  heading.textContent = "Section" + " " + num;
  p1.textContent =
    "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.";
  p2.textContent =
    "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.";

  return newSection;
}


/* LISTENERS */
newSectionBtn.addEventListener("click", () => {
  newSectionBtn.insertAdjacentHTML("beforebegin", "<li> Section" + " " + n + "</li>");
  main.appendChild(duplicate(n));
  main.lastElementChild.scrollIntoView({
    behavior: "smooth"
  });
  n++;
});

backBtn.addEventListener("click", () => {
  window.scrollTo({
    top: 0,
    behavior: "smooth"
  });
});

/*
 *
 * CSS written based on SMACSS architecture.
 * To learn more, visit: http://smacss.com/
 * 
 * For simplicity, no reset or normalize is added. 
 * To learn more, visit: https://css-tricks.com/reboot-resets-reasoning/
 *
*/


/* ---- Base Rules ---- */

body {
  background: rgb(136, 203, 171);
  background: linear-gradient(0deg, rgba(136, 203, 171, 1) 0%, rgba(0, 13, 60, 1) 100%);
  margin: 0;
  font-family: "Merriweather", serif;
  color: #fff;
}


/* Typeography General*/

h1 {
  font-family: "Fira Sans", sans-serif;
  font-size: 3em;
  margin: 2em 1rem;
}

@media only screen and (min-width: 35em) {
  h1 {
    font-size: 7em;
    margin: 2em 4rem 1em;
  }
}

h2 {
  border-bottom: 1px solid #cc1;
  font-family: "Oxygen", Sans-Serif;
  font-size: 3em;
  color: #fff;
}

p {
  line-height: 1.6em;
  color: #eee;
}


/* ---- Layout Rules ---- */

main {
  margin: 10vh 1em 10vh;
}

.main-hero {
  min-height: 40vh;
  padding-top: 3em;
}

section {
  position: relative;
  min-height: 80vh;
}


/* ---- Module Rules ---- */


/* Navigation Styles*/

.navbar__menu ul {
  padding-left: 0;
  margin: 0;
  text-align: right;
}

.navbar__menu li {
  display: inline-block;
}

.navbar__menu .menu__link {
  display: block;
  padding: 1em;
  font-weight: bold;
  text-decoration: none;
  color: #000;
}

.navbar__menu .menu__link:hover {
  background: #333;
  color: #fff;
  transition: ease 0.3s all;
}


/* Header Styles */

.page__header {
  background: #fff;
  position: fixed;
  top: 0;
  width: 100%;
  z-index: 5;
}


/* Footer Styles */

.page__footer {
  background: #000;
  padding: 3em;
  color: #fff;
}

.page__footer p {
  color: #fff;
}


/* ---- Theme Rules ---- */


/* Landing Container Styles */

.landing__container {
  padding: 1em;
  text-align: left;
}

@media only screen and (min-width: 35em) {
  .landing__container {
    max-width: 50em;
    padding: 4em;
  }
}

section:nth-of-type(even) .landing__container {
  margin-right: 0;
  margin-left: auto;
  text-align: right;
}


/* Background Circles */


/* Note that background circles are created with psuedo elements before and after */


/* Circles appear to be random do to use of :nth-of-type psuedo class */

section:nth-of-type(odd) .landing__container::before {
  content: "";
  background: rgba(255, 255, 255, 0.187);
  position: absolute;
  z-index: -5;
  width: 20vh;
  height: 20vh;
  border-radius: 50%;
  opacity: 0;
  transition: ease 0.5s all;
}

section:nth-of-type(even) .landing__container::before {
  content: "";
  background: rgb(255, 255, 255);
  background: linear-gradient(0deg, rgba(255, 255, 255, 0.1) 0%, rgba(255, 255, 255, 0.2) 100%);
  position: absolute;
  top: 3em;
  right: 3em;
  z-index: -5;
  width: 10vh;
  height: 10vh;
  border-radius: 50%;
  opacity: 0;
  transition: ease 0.5s all;
}

section:nth-of-type(3n) .landing__container::after {
  content: "";
  background: rgb(255, 255, 255);
  background: linear-gradient(0deg, rgba(255, 255, 255, 0.1) 0%, rgba(255, 255, 255, 0.2) 100%);
  position: absolute;
  right: 0;
  bottom: 0;
  z-index: -5;
  width: 10vh;
  height: 10vh;
  border-radius: 50%;
  opacity: 0;
  transition: ease 0.5s all;
}

section:nth-of-type(3n + 1) .landing__container::after {
  content: "";
  background: rgb(255, 255, 255);
  background: linear-gradient(0deg, rgba(255, 255, 255, 0.1) 0%, rgba(255, 255, 255, 0.2) 100%);
  position: absolute;
  right: 20vw;
  bottom: -5em;
  z-index: -5;
  width: 15vh;
  height: 15vh;
  border-radius: 50%;
  opacity: 0;
  transition: ease 0.5s all;
}


/* ---- Theme State Rules ---- */


/* Section Active Styles */


/* Note: your-active-class class is applied through javascript. You should update the class here and in the index.html to what you set in your javascript file.  */

section.your-active-class {
  background: rgb(0, 0, 0);
  background: linear-gradient(0deg, rgba(0, 0, 0, 0.1) 0%, rgba(0, 0, 0, 0) 100%);
}

section.your-active-class .landing__container::before {
  opacity: 1;
  animation: rotate 4s linear 0s infinite forwards;
}

section.your-active-class .landing__container::after {
  opacity: 1;
  animation: rotate 5s linear 0s infinite forwards reverse;
}


/* Section Active Styles Keyframe Animations */

@keyframes rotate {
  from {
    transform: rotate(0deg) translate(-1em) rotate(0deg);
  }
  to {
    transform: rotate(360deg) translate(-1em) rotate(-360deg);
  }
}


/* MY STYLES */

.flex-container {
  display: flex;
  flex-flow: row wrap;
  justify-content: space-evenly;
  background-color: #00c3c7;
  border-radius: 8px;
  position: fixed;
  top: 0px;
  width: 95%;
  min-height: 100px;
  z-index: 10000;
}

li {
  padding: 10px;
  list-style-type: none;
  background-color: cadetblue;
  border-radius: 8px;
  align-self: center;
}

li:hover {
  cursor: pointer;
}

.active {
  background-color: darkred;
  font-size: 100px;
}

JavaScript:

<!DOCTYPE html>
<html lang="en">

<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" />
</head>

<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 id="main">
    <header class="main__hero">
      <nav>
        <ul class="flex-container">
          <li>Section 1</li>
          <li>Section 2</li>
          <li>Section 3</li>
          <li id="new-section">NEW SECTION</li>
          <li id="back">BACK TO TOP</li>
        </ul>
      </nav>
      <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" class="your-active-class">
      <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>
    <section id="section3" data-nav="Section 3">
      <div class="landing__container">
        <h2>Section 3</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>&copy Udacity</p>
  </footer>
  <script src="/js/app.js"></script>
</body>

</html>

Answer 1

你可以这样做：

References 阅读 link 了解 isInViewport 函数的工作原理。

我为处理多个元素而添加的每个部分。 if 部分决定何时做某事。

        var isInViewport = function(elem) {
          var distance = elem.getBoundingClientRect();
          return (
            distance.top >= 0 &&
            distance.left >= 0 &&
            distance.bottom <= (window.innerHeight || document.documentElement.clientHeight) &&
            distance.right <= (window.innerWidth || document.documentElement.clientWidth)
          );
        };
    // read the link on how above code works
     
window.addEventListener('scroll', function(event) {
// add event on scroll
  var findMe = document.querySelectorAll('h2');
  var li = document.querySelectorAll('li');
// on scroll fetch H2 and li elements, on scroll in order to get new dynamically added with button
  findMe.forEach(element => {
//for each h2
    if (isInViewport(element)) {
//if in Viewport
        li.forEach(li => {
          li.style.color = 'white';
        })
//set all li styles to none in order to remove before added
        li.forEach(li => {
//for each li
          if (li.innerHTML.trim() === element.innerHTML.trim()) {
//if li text is same as curent element in viport text 
            li.style.color = 'red';
//add style
          }
        })
    }
  });
}, false);

出于某种原因，它不适用于部分或包装 div，它适用于内部包含内容的元素。

所以需要针对H2元素，制定条件

示例：

/* VARIABLES */
const newSectionBtn = document.getElementById("new-section");
const main = document.getElementById("main");
const backBtn = document.getElementById("back");
let allLists = document.getElementsByTagName("li");
let allSections = document.getElementsByTagName("section");
let n = 4;

/* FUNCTIONS */
function duplicate(num) {
  const newSection = document.createElement("section");
  const newDiv = document.createElement("div");
  const heading = document.createElement("h2");
  const p1 = document.createElement("p");
  const p2 = document.createElement("p");

  newSection.appendChild(newDiv);
  newDiv.appendChild(heading);
  newDiv.appendChild(p1);
  newDiv.appendChild(p2);

  newSection.setAttribute("id", "section" + num);
  newSection.setAttribute("data-nav", "Section" + " " + num);
  newDiv.setAttribute("class", "landing__container");

  heading.textContent = "Section" + " " + num;
  p1.textContent =
    "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.";
  p2.textContent =
    "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.";

  return newSection;
}


/* LISTENERS */
newSectionBtn.addEventListener("click", () => {
  newSectionBtn.insertAdjacentHTML("beforebegin", "<li> Section" + " " + n + "</li>");
  main.appendChild(duplicate(n));
  main.lastElementChild.scrollIntoView({
    behavior: "smooth"
  });
  n++;
});

backBtn.addEventListener("click", () => {
  window.scrollTo({
    top: 0,
    behavior: "smooth"
  });
});


var isInViewport = function(elem) {
  var distance = elem.getBoundingClientRect();
  return (
    distance.top >= 0 &&
    distance.left >= 0 &&
    distance.bottom <= (window.innerHeight || document.documentElement.clientHeight) &&
    distance.right <= (window.innerWidth || document.documentElement.clientWidth)
  );
};


window.addEventListener('scroll', function(event) {
  var findMe = document.querySelectorAll('h2');
  var li = document.querySelectorAll('li');
  findMe.forEach(element => {
    if (isInViewport(element)) {
        li.forEach(li => {
          li.style.color = 'white';
        })
        li.forEach(li => {
          if (li.innerHTML.trim() === element.innerHTML.trim()) {
            li.style.color = 'red';
          }
        })
    }
  });
}, false);

/*
 *
 * CSS written based on SMACSS architecture.
 * To learn more, visit: http://smacss.com/
 * 
 * For simplicity, no reset or normalize is added. 
 * To learn more, visit: https://css-tricks.com/reboot-resets-reasoning/
 *
*/


/* ---- Base Rules ---- */

body {
  background: rgb(136, 203, 171);
  background: linear-gradient(0deg, rgba(136, 203, 171, 1) 0%, rgba(0, 13, 60, 1) 100%);
  margin: 0;
  font-family: "Merriweather", serif;
  color: #fff;
}


/* Typeography General*/

h1 {
  font-family: "Fira Sans", sans-serif;
  font-size: 3em;
  margin: 2em 1rem;
}

@media only screen and (min-width: 35em) {
  h1 {
    font-size: 7em;
    margin: 2em 4rem 1em;
  }
}

h2 {
  border-bottom: 1px solid #cc1;
  font-family: "Oxygen", Sans-Serif;
  font-size: 3em;
  color: #fff;
}

p {
  line-height: 1.6em;
  color: #eee;
}


/* ---- Layout Rules ---- */

main {
  margin: 10vh 1em 10vh;
}

.main-hero {
  min-height: 40vh;
  padding-top: 3em;
}

section {
  position: relative;
  min-height: 80vh;
}


/* ---- Module Rules ---- */


/* Navigation Styles*/

.navbar__menu ul {
  padding-left: 0;
  margin: 0;
  text-align: right;
}

.navbar__menu li {
  display: inline-block;
}

.navbar__menu .menu__link {
  display: block;
  padding: 1em;
  font-weight: bold;
  text-decoration: none;
  color: #000;
}

.navbar__menu .menu__link:hover {
  background: #333;
  color: #fff;
  transition: ease 0.3s all;
}


/* Header Styles */

.page__header {
  background: #fff;
  position: fixed;
  top: 0;
  width: 100%;
  z-index: 5;
}


/* Footer Styles */

.page__footer {
  background: #000;
  padding: 3em;
  color: #fff;
}

.page__footer p {
  color: #fff;
}


/* ---- Theme Rules ---- */


/* Landing Container Styles */

.landing__container {
  padding: 1em;
  text-align: left;
}

@media only screen and (min-width: 35em) {
  .landing__container {
    max-width: 50em;
    padding: 4em;
  }
}

section:nth-of-type(even) .landing__container {
  margin-right: 0;
  margin-left: auto;
  text-align: right;
}


/* Background Circles */


/* Note that background circles are created with psuedo elements before and after */


/* Circles appear to be random do to use of :nth-of-type psuedo class */

section:nth-of-type(odd) .landing__container::before {
  content: "";
  background: rgba(255, 255, 255, 0.187);
  position: absolute;
  z-index: -5;
  width: 20vh;
  height: 20vh;
  border-radius: 50%;
  opacity: 0;
  transition: ease 0.5s all;
}

section:nth-of-type(even) .landing__container::before {
  content: "";
  background: rgb(255, 255, 255);
  background: linear-gradient(0deg, rgba(255, 255, 255, 0.1) 0%, rgba(255, 255, 255, 0.2) 100%);
  position: absolute;
  top: 3em;
  right: 3em;
  z-index: -5;
  width: 10vh;
  height: 10vh;
  border-radius: 50%;
  opacity: 0;
  transition: ease 0.5s all;
}

section:nth-of-type(3n) .landing__container::after {
  content: "";
  background: rgb(255, 255, 255);
  background: linear-gradient(0deg, rgba(255, 255, 255, 0.1) 0%, rgba(255, 255, 255, 0.2) 100%);
  position: absolute;
  right: 0;
  bottom: 0;
  z-index: -5;
  width: 10vh;
  height: 10vh;
  border-radius: 50%;
  opacity: 0;
  transition: ease 0.5s all;
}

section:nth-of-type(3n + 1) .landing__container::after {
  content: "";
  background: rgb(255, 255, 255);
  background: linear-gradient(0deg, rgba(255, 255, 255, 0.1) 0%, rgba(255, 255, 255, 0.2) 100%);
  position: absolute;
  right: 20vw;
  bottom: -5em;
  z-index: -5;
  width: 15vh;
  height: 15vh;
  border-radius: 50%;
  opacity: 0;
  transition: ease 0.5s all;
}


/* ---- Theme State Rules ---- */


/* Section Active Styles */


/* Note: your-active-class class is applied through javascript. You should update the class here and in the index.html to what you set in your javascript file.  */

section.your-active-class {
  background: rgb(0, 0, 0);
  background: linear-gradient(0deg, rgba(0, 0, 0, 0.1) 0%, rgba(0, 0, 0, 0) 100%);
}

section.your-active-class .landing__container::before {
  opacity: 1;
  animation: rotate 4s linear 0s infinite forwards;
}

section.your-active-class .landing__container::after {
  opacity: 1;
  animation: rotate 5s linear 0s infinite forwards reverse;
}


/* Section Active Styles Keyframe Animations */

@keyframes rotate {
  from {
    transform: rotate(0deg) translate(-1em) rotate(0deg);
  }
  to {
    transform: rotate(360deg) translate(-1em) rotate(-360deg);
  }
}


/* MY STYLES */

.flex-container {
  display: flex;
  flex-flow: row wrap;
  justify-content: space-evenly;
  background-color: #00c3c7;
  border-radius: 8px;
  position: fixed;
  top: 0px;
  width: 95%;
  min-height: 100px;
  z-index: 10000;
}

li {
  padding: 10px;
  list-style-type: none;
  background-color: cadetblue;
  border-radius: 8px;
  align-self: center;
}

li:hover {
  cursor: pointer;
}

.active {
  background-color: darkred;
  font-size: 100px;
}

JavaScript:

<!DOCTYPE html>
<html lang="en">

<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" />
</head>

<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 id="main">
    <header class="main__hero">
      <nav>
        <ul class="flex-container">
          <li>Section 1</li>
          <li>Section 2</li>
          <li>Section 3</li>
          <li id="new-section">NEW SECTION</li>
          <li id="back">BACK TO TOP</li>
        </ul>
      </nav>
      <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" class="your-active-class">
      <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>
    <section id="section3" data-nav="Section 3">
      <div class="landing__container">
        <h2>Section 3</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>&copy Udacity</p>
  </footer>
  <script src="/js/app.js"></script>
</body>

</html>

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