HTML

<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>

CSS


        :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);
    }
}

JS


        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();