Web Vitals patterns

A collection of common UX patterns optimized for Core Web Vitals. This collection includes patterns that are often tricky to implement without hurting your Core Web Vitals scores. You can use the code in these examples to help ensure your projects stay on the right track.

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Infinite Scroll

Infinite scroll is a UX pattern where content is continuously added to the page as a user scrolls. Some implementations of infinite scroll can be a source of layout shifts.

Infinite scroll

<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);
    }
}

In this implementation of infinite scroll there are never any layout shifts - regardless of how long it takes the server to respond with new content.

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