How to load content on scrolling in website with JavaScript?

Question

I have seen many sites load whenever you scroll. How to do the same thing on my site?

Intersection Observer API

Bqardi
– Bqardi

2022-11-19 11:53:14 +00:00
Commented Nov 19, 2022 at 11:53 — Bqardi
– Bqardi, Commented Nov 19, 2022 at 11:53

FreePhoenix888 · Accepted Answer · 2022-11-19 11:55:20Z

It would be better if you provide us an example what websites you mean. Ok. I will imagine that you are talking about a website like Pinterest that shows you content as much as you scroll it. It is not hard. You just have to get data from a server when user is for example at the end of the page

Add a listener on the scroll

window.addEventListener("scroll", scrollHandler);

Find out if a user is at the end of a page in the scroll listener:

const endOfPage = window.innerHeight + window.pageYOffset >= document.body.offsetHeight;

Get new content from a server
Add new content to a page

Example:

const cardContainer = document.getElementById("card-container");
const cardCountElem = document.getElementById("card-count");
const cardTotalElem = document.getElementById("card-total");
const loader = document.getElementById("loader");

const cardLimit = 99;
const cardIncrease = 9;
const pageCount = Math.ceil(cardLimit / cardIncrease);
let currentPage = 1;

cardTotalElem.innerHTML = cardLimit;

var throttleTimer;
const throttle = (callback, time) => {
  if (throttleTimer) return;

  throttleTimer = true;

  setTimeout(() => {
    callback();
    throttleTimer = false;
  }, time);
};

const getRandomColor = () => {
  const h = Math.floor(Math.random() * 360);

  return `hsl(${h}deg, 90%, 85%)`;
};

const createCard = (index) => {
  const card = document.createElement("div");
  card.className = "card";
  card.innerHTML = index;
  card.style.backgroundColor = getRandomColor();
  cardContainer.appendChild(card);
};

const addCards = (pageIndex) => {
  currentPage = pageIndex;

  const startRange = (pageIndex - 1) * cardIncrease;
  const endRange =
    currentPage == pageCount ? cardLimit : pageIndex * cardIncrease;

  cardCountElem.innerHTML = endRange;

  for (let i = startRange + 1; i <= endRange; i++) {
    createCard(i);
  }
};

const handleInfiniteScroll = () => {
  throttle(() => {
    const endOfPage =
      window.innerHeight + window.pageYOffset >= document.body.offsetHeight;

    if (endOfPage) {
      addCards(currentPage + 1);
    }

    if (currentPage === pageCount) {
      removeInfiniteScroll();
    }
  }, 1000);
};

const removeInfiniteScroll = () => {
  loader.remove();
  window.removeEventListener("scroll", handleInfiniteScroll);
};

window.onload = function () {
  addCards(currentPage);
};

window.addEventListener("scroll", handleInfiniteScroll);

body {
  font-family: "Roboto", sans-serif;
}

#card-container {
  display: flex;
  flex-wrap: wrap;
}

.card {
  height: 55vh;
  width: calc((100% / 3) - 16px);
  margin: 8px;
  border-radius: 3px;
  transition: all 200ms ease-in-out;
  display: flex;
  align-items: center;
  justify-content: center;
}

.card:hover {
  box-shadow: 0 4px 10px rgba(0, 0, 0, 0.2);
}

.card-actions {
  margin: 8px;
  padding: 16px 0;
  display: flex;
  justify-content: space-between;
  align-items: center;
}

#loader {
  display: flex;
}

.skeleton-card {
  height: 55vh;
  width: calc((100% / 3) - 16px);
  margin: 8px;
  border-radius: 3px;
  transition: all 200ms ease-in-out;
  position: relative;
  background-color: #eaeaea;
}

.skeleton-card::after {
  content: "";
  position: absolute;
  top: 0;
  right: 0;
  bottom: 0;
  left: 0;
  transform: translateX(-100%);
  background-image: linear-gradient(90deg, rgba(255, 255, 255, 0) 0, rgba(255, 255, 255, 0.2) 20%, rgba(255, 255, 255, 0.5) 60%, rgba(255, 255, 255, 0));
  animation: load 1s infinite;
}

@keyframes load {
  100% {
    transform: translateX(100%);
  }
}

@media screen and (prefers-reduced-motion: reduce) {
  .skeleton-card::after {
    animation: none;
  }
}

<div id="card-container">
</div>
<div id="loader">
  <div class="skeleton-card"></div>
  <div class="skeleton-card"></div>
  <div class="skeleton-card"></div>
</div>
<div class="card-actions">
  <span>Showing 
    <span id="card-count"></span> of 
    <span id="card-total"></span> cards      
  </span>
</div>

Note: It is better to open this example in the full-page mode

The source

Usitha Indeewara · Accepted Answer · 2022-11-20 07:35:18Z

You have to use Intersection Observer API

let options = {
  root: document.querySelector('#scrollArea'),
  rootMargin: '0px',
  threshold: 1.0
}

let observer = new IntersectionObserver(callback, options);

function callback() {
    // Something like showing a hidden element or css animation
}

The above code will call callback function when the users scrolls over a section with id scrollArea

Here is another example:

const observer = new IntersectionObserver((entries) => {
    entries.forEach((entry) => {
        console.log(entry);
        if(entry.isIntersecting) {
            entry.target.classList.add("show");
        } else {
            entry.target.classList.remove("show");
        }
    })
})


const hiddens = document.querySelectorAll(".hidden");
hiddens.forEach(val => {
    observer.observe(val);
});

body {
    font-family: 'Courier New', Courier, monospace;
    background-color: #131316;
    color: #ffffff;
    padding: 0;
    margin: 0;
}

section, h1.cen {
    display: grid;
    place-items: center;
    align-content: center;
    min-height: 100vh;
}

.hidden {
    opacity: 0;
    transition: all 3s;
}

.show {
    opacity: 1;
    
}

<!DOCTYPE html>
<html lang="en">
<head>
    <title>SCROLL</title>
</head>
<body>
    <h1 class="cen">Scroll more</h1>
    <section class="hidden">
        <h1>Hello World</h1>
        <p>This is my scroll animation website</p>
    </section>

    <section class="hidden">
        <h2>Buy my product</h2>
        <p>Just a demo</p>
    </section>

    <section class="hidden">
        <h2>It's really good</h2>

    </section>
</body>
</html>

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