Web Vitals patterns

<div id="carousel">
  <div id="slide-container">
    <div class="slide" data-slideIndex="0">
      <div class="slide-banner">Tour the Empire State Building! <a href="">Buy tickets now.</a></div>
      <img width="1200" height="600" src="./newyork.jpg">
    </div>
    <div class="slide" data-slideIndex="1">
      <div class="slide-banner">Ride the Shinkansen! <a href="">Buy tickets now.</a></div>
      <img width="1200" height="600" src="./tokyo.jpg">
    </div>
    <div class="slide" data-slideIndex="2">
      <div class="slide-banner">Discover relaxation! <a href="">Buy tickets now.</a></div>
      <img width="1200" height="600" src="./beach.jpg">
    </div>
    <div class="slide" data-slideIndex="3">
      <div class="slide-banner">See penguins! <a href="">Buy tickets now.</a></div>
      <img width="1200" height="600" src="./penguins.jpg">
    </div>
    <div class="slide" data-slideIndex="4">
      <div class="slide-banner">Take a ride on the wheel! <a href="">Buy tickets now.</a></div>
      <img width="1200" height="600" src="./wheel.jpg">
    </div>
  </div>
  <div id="back-button" class="arrow back">←</div>
  <div id="forward-button" class="arrow forward">→</div>
  <div class="slide-indicators">
    <div class="slide-indicator active"></div>
    <div class="slide-indicator"></div>
    <div class="slide-indicator"></div>
    <div class="slide-indicator"></div>
    <div class="slide-indicator"></div>
  </div>
</div>

function autoplayCarousel() {
    const carouselEl = document.getElementById("carousel");
    const slideContainerEl = carouselEl.querySelector("#slide-container");
    const slideEl = carouselEl.querySelector(".slide");
    let slideWidth = slideEl.offsetWidth;
    // Add click handlers
    document.querySelector("#back-button")
        .addEventListener("click", () => navigate("backward"));
    document.querySelector("#forward-button")
        .addEventListener("click", () => navigate("forward"));
    document.querySelectorAll(".slide-indicator")
        .forEach((dot, index) => {
            dot.addEventListener("click", () => navigate(index));
            dot.addEventListener("mouseenter", () => clearInterval(autoplay));
        });
    // Add keyboard handlers
    document.addEventListener('keydown', (e) => {
        if (e.code === 'ArrowLeft') {
            clearInterval(autoplay);
            navigate("backward");
        } else if (e.code === 'ArrowRight') {
            clearInterval(autoplay);
            navigate("forward");
        }
    });
    // Add resize handler
    window.addEventListener('resize', () => {
        slideWidth = slideEl.offsetWidth;
    });
    // Autoplay
    const autoplay = setInterval(() => navigate("forward"), 3000);
    slideContainerEl.addEventListener("mouseenter", () => clearInterval(autoplay));
    // Slide transition
    const getNewScrollPosition = (arg) => {
        const gap = 10;
        const maxScrollLeft = slideContainerEl.scrollWidth - slideWidth;
        if (arg === "forward") {
            const x = slideContainerEl.scrollLeft + slideWidth + gap;
            return x <= maxScrollLeft ? x : 0;
        } else if (arg === "backward") {
            const x = slideContainerEl.scrollLeft - slideWidth - gap;
            return x >= 0 ? x : maxScrollLeft;
        } else if (typeof arg === "number") {
            const x = arg * (slideWidth + gap);
            return x;
        }
    }
    const navigate = (arg) => {
        slideContainerEl.scrollLeft = getNewScrollPosition(arg);
    }
    // Slide indicators
    const slideObserver = new IntersectionObserver((entries, observer) => {
        entries.forEach(entry => {
            if (entry.isIntersecting) {
                const slideIndex = entry.target.dataset.slideindex;
                carouselEl.querySelector('.slide-indicator.active').classList.remove('active');
                carouselEl.querySelectorAll('.slide-indicator')[slideIndex].classList.add('active');
            }
        });
    }, { root: slideContainerEl, threshold: .1 });
    document.querySelectorAll('.slide').forEach((slide) => {
        slideObserver.observe(slide);
    });
}
autoplayCarousel();

#carousel {
    max-width: 1200px;
    display: flex;
    flex-direction: column;
    margin: 0 auto;
    position: relative;
}  
.slide-indicators {
    display: flex;
    justify-content: center;
}
.slide-indicator {
    height: 44px;
    width: 50px;
    display: flex;
    justify-items: center;
    cursor: pointer;
}
.slide-indicator:after {
    content: "";
    background-color: #878787;
    height: 10px;
    margin-top: 10px;
    width: 40px;
}
.slide-indicator.active:after,
.slide-indicator:hover:after {
    background-color: #000000;
}
.slide-banner {
    background-color: #000000;
    color: #ffffff;
    position: absolute;
    left: 0;
    bottom: 20px;
    padding: 15px;
    font-size: 2.5vw;
}
.slide-banner a {
    color: #ffffff;
}
#slide-container {
    scroll-snap-type: x mandatory;
    overflow-x: scroll;
    overflow-y: hidden;
    display: flex;
    align-items: center;
    height: 100%;
    gap: 10px;
    -webkit-overflow-scrolling: touch;
    scroll-behavior: smooth;
}
.slide {
    scroll-snap-align: center;
    position: relative;
    min-width: 100%;
    padding-top: 50%;
}
.slide img {
    height: 100%;
    width: auto;
    position: absolute;
    top: 0;
    left: 0;
}
.arrow {
    color: #ffffff;
    height: 20px;
    width: 20px;
    background-color: #000000;
    position: absolute;
    padding: 10px;
    opacity: .3;
    cursor: pointer;
}
.arrow.back {
    left: 10px;
    top: 10px;
}
.arrow.forward {
    right: 10px;
    top: 10px;
}
.arrow:hover {
    opacity: 1;
}

<head>
    <style>
        @font-face {
            font-family: 'Google Sans';
            src: url("GoogleSans-Regular.woff2") format('woff2');
            font-display: swap;
        }
        body {
            font-family: system-ui;
            font-size: 1em;
        }
        h1 {
            font-family: 'Google Sans', sans-serif;
            font-size: 3em;
        }
    </style>
</head>

<head>
    <link rel="preconnect" href="https://fonts.googleapis.com">
    <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin>
    <link href="https://fonts.googleapis.com/css2?family=Zen+Tokyo+Zoo&display=swap" rel="stylesheet">
    <style>
        body {
            font-family: system-ui;
            font-size: 1em;
        }
        h1 {
            font-family: 'Zen Tokyo Zoo', sans-serif;
            font-size: 3em;
        }
    </style>
</head>

<img width="267" height="400" src="dog.jpg">

<!-- Using density descriptors -->
<img width="480" height="330"
    srcset="cat-1x.jpg, cat-2x.jpg 2x, cat-3x.jpg 3x"
    src="cat-1x.jpg"
    alt="Photo of a cat on a green background">
<!-- Using width descriptors -->    
<img width="256" height="128"
    srcset="dog-256w.jpg 256w, dog-512w.jpg 512w, dog-1028w.jpg 1028w"
    src="dog-256w.jpg"
    alt="Photo of a dog on a orange background">
<!-- Picture tag -->
<picture>
    <source media="(max-width: 720px)" width="600" height="300" srcset="newyork-rectangle.jpg" />
    <source media="(min-width: 721px)" width="600" height="600" srcset="newyork-square-1x.jpg, newyork-square-2x.jpg 2x, newyork-square-3x.jpg 3x" />
    <img src="newyork-rectangle.jpg" width="600" height="300" alt="Photo of the Empire State Building">
</picture>

<div id="infinite-scroll-container">
    <div id="sentinel"></div>
    <div class="item">A</div>
    <div class="item">B</div>
    <div class="item">C</div>
    <div class="item">D</div>
    <div class="item">E</div>
    <button id="infinite-scroll-button" disabled>
        <span class="disabled-text">Loading more items...</span>
        <span class="active-text">Show more</span>
    </button>
</div>

function infiniteScroll() {
    let responseBuffer = [];
    let hasMore;
    let requestPending = false;
    const loadingButtonEl = document.querySelector('#infinite-scroll-button');
    const containerEl = document.querySelector('#infinite-scroll-container');
    const sentinelEl = document.querySelector("#sentinel");
    const insertNewItems = () => {
        while (responseBuffer.length > 0) {
            const data = responseBuffer.shift();
            const el = document.createElement("div");
            el.textContent = data;
            el.classList.add("item");
            el.classList.add("new");
            containerEl.insertBefore(el, loadingButtonEl);
            console.log(`inserted: ${data}`);
        }
        sentinelObserver.observe(sentinelEl);
        if (hasMore === false) {
            loadingButtonEl.style = "display: none";
            sentinelObserver.unobserve(sentinelEl);
            listObserver.unobserve(loadingButtonEl);
        }
        loadingButtonEl.disabled = true
    }
    loadingButtonEl.addEventListener("click", insertNewItems);
    const requestHandler = () => {
        if (requestPending) return;
        console.log("making request");
        requestPending = true;
        fakeServer.fakeRequest().then((response) => {
            console.log("server response", response);
            requestPending = false;
            responseBuffer = responseBuffer.concat(response.items);
            hasMore = response.hasMore;
            loadingButtonEl.disabled = false;;
        });
    }
    const sentinelObserver = new IntersectionObserver((entries, observer) => {
        entries.forEach(entry => {
            if (entry.intersectionRatio > 0) {
                observer.unobserve(sentinelEl);
                requestHandler();
            }
        });
    });
    const listObserver = new IntersectionObserver((entries, observer) => {
        entries.forEach(entry => {
            if (entry.intersectionRatio > 0 && entry.intersectionRatio < 1) {
                insertNewItems();
            }
        });
    }, {
        rootMargin: "0px 0px 200px 0px"
    });
    sentinelObserver.observe(sentinelEl);
    listObserver.observe(loadingButtonEl);
}
infiniteScroll();

:root {
    --active-button-primary: #0080ff;
    --active-button-font:#ffffff;
    --disabled-button-primary: #f5f5f5;
    --disabled-button-secondary: #c4c4c4;
    --disabled-button-font: #000000;
}
#infinite-scroll-container {
    position: relative;
}
#sentinel {
    position: absolute;
    bottom: 150vh;
}
#infinite-scroll-button {
    cursor: pointer;
    border: none;
    padding: 1em;
    width: 100%;
    font-size: 1em;
}
#infinite-scroll-button:enabled {
    color: var(--active-button-font);
    background-color: var(--active-button-primary)
}
#infinite-scroll-button:disabled {
    color: var(--disabled-button-font);
    background-color: var(--disabled-button-primary);
    cursor: not-allowed;
    animation: 3s ease-in-out infinite loadingAnimation;
}
#infinite-scroll-button:enabled .disabled-text {
    display: none;
}
#infinite-scroll-button:disabled .active-text {
    display: none;
}
@keyframes loadingAnimation {
    0% {
        background-color: var(--disabled-button-primary);
    }
    50% {
        background-color: var(--disabled-button-secondary);
    }
    100% {
        background-color: var(--disabled-button-primary);
    }
}

<div id="banner" class="banner">
  <button id="close-button" class="close-button" aria-label="close" tabindex="0">✕</button>
  <div>
    <h1>Notice</h1>
    Lorem ipsum dolor sit amet.
  </div>
</div>

document.getElementById("close-button").onclick = () => {
    document.getElementById("banner").style.display = "none";
}

body {
    overscroll-behavior-y: none;
    font-family: system-ui;
    padding: 2em;
    background-color: #f4f4f4;
}
.banner {
    animation: slideIn 1000ms ease-in-out;
    position: fixed;
    left: 0;
    bottom: 0;
    right: 0;
    padding: 1rem;
    background-color: white;
    box-shadow: 0 0 10px rgba(0,0,0,0.2);
}
@keyframes slideIn {
    from {
        transform: translateY(100vh);
    }
    to {
        transform: translateY(0vh);
    }
}
.close-button {
    background: transparent;
    border: none;
    padding: 1em;
    font-size: 1em;
    position: absolute;
    right: 0;
    top: 0;
    cursor: pointer;
}

<div id="modal" class="modal">
    <button id="close-button" class="close-button" aria-label="close" tabindex="0">✕</button>
    <div>
        <h1>Notice</h1>
        Lorem ipsum dolor sit amet.
    </div>
</div>

document.getElementById("close-button").onclick = () => {
    document.getElementById("modal").style.display = "none";
}

body {
    overscroll-behavior-y: none;
    font-family: system-ui;
    padding: 2em;
    background-color: #f4f4f4;
}
.modal {
    position: fixed;
    top: 50%;
    left: 50%;
    min-width: 66%;
    transform: translate(-50%, -50%);
    padding: 1em 2em 2em 2em;
    background-color: white;
    box-shadow: 0 0 15px rgba(0,0,0,0.2);
}
.close-button {
    background: transparent;
    border: none;
    padding: 1em;
    font-size: 1em;
    position: absolute;
    right: 0;
    top: 0;
    cursor: pointer;
}

<div id="banner" class="banner">
    <button id="close-button" class="close-button" aria-label="close" tabindex="0">✕</button>
    <div>
        <h1>Notice</h1>
        Lorem ipsum dolor sit amet.
    </div>
</div>

document.getElementById("close-button").onclick = () => {
    document.getElementById("banner").style.display = "none";
}

body {
    font-family: system-ui;
    padding: 2em;
    overscroll-behavior-y: none;
    background-color: #f4f4f4;
}
.banner {
    position: fixed;
    left: 0;
    bottom: 0;
    right: 0;
    padding: 1rem;
    background-color: white;
    box-shadow: 0 0 10px rgba(0,0,0,0.2);
}
.close-button {
    background: transparent;
    border: none;
    padding: 1em;
    font-size: 1em;
    position: absolute;
    right: 0;
    top: 0;
    cursor: pointer;
}

<div class="grid">
    <div class="item">
        <div class="image-container">
            <img src="hats.jpg">
        </div>
        <div class="text-container">Hats</div>
    </div>
    <div class="item empty">
        <div class="image-container">
            <img src="">
        </div>
        <div class="text-container">Watches</div>
    </div>
    <div class="item empty">
        <div class="image-container">
            <img src="">
        </div>
        <div class="text-container"></div>
    </div>
    <div class="item empty">
        <div class="image-container">
            <img src="">
        </div>
        <div class="text-container"></div>
    </div>
    <div class="item empty">
        <div class="image-container">
            <img src="">
        </div>
        <div class="text-container"></div>
    </div>
    <div class="item empty">
        <div class="image-container">
            <img src="">
        </div>
        <div class="text-container"></div>
    </div>
</div>

const data = [
    {
        description: "Watches",
        src: "https://web-dev.imgix.net/image/j2RDdG43oidUy6AL6LovThjeX9c2/GMPpoERpp9aM5Rihk5F2.jpg"
    },
    {
        description: "Shirt",
        src: "shirt.jpg"
    },
    {
        description: "Shorts",
        src: "shorts.jpg"
    },
    {
        description: "Sunglasses",
        src: "sunglasses.jpg"
    },
    {
        description: "Shoes",
        src: "shoes.jpg"
    }
];
document.querySelectorAll(".item.empty").forEach((el, index) => {
    if (data[index]) {
        el.classList = "item loaded";
        el.querySelector("img").src = data[index].src;
        el.querySelector(".text-container").innerHTML = data[index].description;
    }
});

:root {
    --placeholder-primary: #eeeeee;
    --placeholder-secondary: #cccccc;
}
.grid {
    display: flex;
    flex-direction: row;
    flex-wrap: wrap;
    justify-content: center;
    gap: 1em;
    width: 100%;
    max-width: 650px;
    margin: 1em 0em;
}
.item {
    display: grid;
    gap: .5em;
    width: 200px;
}
.text-container {
    font-size: 1em;
    height: 1.5em;
    text-align: center;
    font-weight: bold;
}
.image-container {
    width: 200px;
    height: 200px;;
    animation: placeholder ease-in-out 2s infinite;
}
.image-container img {
    width: 100%;
}
@keyframes placeholder {
    0% {
        background-color: var(--placeholder-primary);
    }
    50% {
        background-color: var(--placeholder-secondary);
    }
    100% {
        background-color: var(--placeholder-primary);
    }
}
@keyframes fadeIn {
    0% {
        opacity: 0%;
    }
    100% {
        opacity: 100%;
    }
}
.item.loaded .image-container {
    animation: none;
}
.item.loaded .image-container img{
    animation: fadeIn linear .5s;
}

<video controls width="960" height="540" poster="flower-960-poster.png">
    <source src="flower-960.mp4" type="video/mp4">
</video>

video {
    max-width: 100%;
    height: auto;
}

<video autoplay loop muted playsinline width="320" height="240">
    <source src="dog.mp4" type="video/mp4">
</video>