1. このページの目的
Web Vitals patterns の Infinite Scroll を試す。
2. デモ
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);
}
}
JavaScript
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();