/**
* A lightweight youtube embed. Still should feel the same to the user, just MUCH faster to initialize and paint.
*
* Thx to these as the inspiration
* https://storage.googleapis.com/amp-vs-non-amp/youtube-lazy.html
* https://autoplay-youtube-player.glitch.me/
*
* Once built it, I also found these:
* https://github.com/ampproject/amphtml/blob/master/extensions/amp-youtube (👍👍)
* https://github.com/Daugilas/lazyYT
* https://github.com/vb/lazyframe
*/
class LiteYTEmbed extends HTMLElement {
connectedCallback() {
this.videoId = this.getAttribute('videoid');
let playBtnEl = this.querySelector('.lty-playbtn');
// A label for the button takes priority over a [playlabel] attribute on the custom-element
this.playLabel = (playBtnEl && playBtnEl.textContent.trim()) || this.getAttribute('playlabel') || 'Play';
/**
* Lo, the youtube placeholder image! (aka the thumbnail, poster image, etc)
*
* See https://github.com/paulirish/lite-youtube-embed/blob/master/youtube-thumbnail-urls.md
*
* TODO: Do the sddefault->hqdefault fallback
* - When doing this, apply referrerpolicy (https://github.com/ampproject/amphtml/pull/3940)
* TODO: Consider using webp if supported, falling back to jpg
*/
if (!this.style.backgroundImage) {
this.style.backgroundImage = `url("https://i.ytimg.com/vi/${this.videoId}/hqdefault.jpg")`;
}
// Set up play button, and its visually hidden label
if (!playBtnEl) {
playBtnEl = document.createElement('button');
playBtnEl.type = 'button';
playBtnEl.classList.add('lty-playbtn');
this.append(playBtnEl);
}
if (!playBtnEl.textContent) {
const playBtnLabelEl = document.createElement('span');
playBtnLabelEl.className = 'lyt-visually-hidden';
playBtnLabelEl.textContent = this.playLabel;
playBtnEl.append(playBtnLabelEl);
}
// On hover (or tap), warm up the TCP connections we're (likely) about to use.
this.addEventListener('pointerover', LiteYTEmbed.warmConnections, {once: true});
// Once the user clicks, add the real iframe and drop our play button
// TODO: In the future we could be like amp-youtube and silently swap in the iframe during idle time
// We'd want to only do this for in-viewport or near-viewport ones: https://github.com/ampproject/amphtml/pull/5003
this.addEventListener('click', this.addIframe);
}
// // TODO: Support the the user changing the [videoid] attribute
// attributeChangedCallback() {
// }
/**
* Add a <link rel={preload | preconnect} ...> to the head
*/
static addPrefetch(kind, url, as) {
const linkEl = document.createElement('link');
linkEl.rel = kind;
linkEl.href = url;
if (as) {
linkEl.as = as;
}
document.head.append(linkEl);
}
/**
* Begin pre-connecting to warm up the iframe load
* Since the embed's network requests load within its iframe,
* preload/prefetch'ing them outside the iframe will only cause double-downloads.
* So, the best we can do is warm up a few connections to origins that are in the critical path.
*
* Maybe `<link rel=preload as=document>` would work, but it's unsupported: http://crbug.com/593267
* But TBH, I don't think it'll happen soon with Site Isolation and split caches adding serious complexity.
*/
static warmConnections() {
if (LiteYTEmbed.preconnected) return;
// The iframe document and most of its subresources come right off youtube.com
LiteYTEmbed.addPrefetch('preconnect', 'https://www.youtube-nocookie.com');
// The botguard script is fetched off from google.com
LiteYTEmbed.addPrefetch('preconnect', 'https://www.google.com');
// Not certain if these ad related domains are in the critical path. Could verify with domain-specific throttling.
LiteYTEmbed.addPrefetch('preconnect', 'https://googleads.g.doubleclick.net');
LiteYTEmbed.addPrefetch('preconnect', 'https://static.doubleclick.net');
LiteYTEmbed.preconnected = true;
}
addIframe(e) {
if (this.classList.contains('lyt-activated')) return;
e.preventDefault();
this.classList.add('lyt-activated');
const params = new URLSearchParams(this.getAttribute('params') || []);
params.append('autoplay', '1');
const iframeEl = document.createElement('iframe');
iframeEl.width = 560;
iframeEl.height = 315;
// No encoding necessary as [title] is safe. https://cheatsheetseries.owasp.org/cheatsheets/Cross_Site_Scripting_Prevention_Cheat_Sheet.html#:~:text=Safe%20HTML%20Attributes%20include
iframeEl.title = this.playLabel;
iframeEl.allow = 'accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture';
iframeEl.allowFullscreen = true;
// AFAIK, the encoding here isn't necessary for XSS, but we'll do it only because this is a URL
// https://stackoverflow.com/q/64959723/89484
iframeEl.src = `https://www.youtube-nocookie.com/embed/${encodeURIComponent(this.videoId)}?${params.toString()}`;
this.append(iframeEl);
// Set focus for a11y
iframeEl.focus();
}
}
// Register custom element
customElements.define('lite-youtube', LiteYTEmbed);
