226 lines
9.5 KiB
JavaScript
226 lines
9.5 KiB
JavaScript
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/**
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* A lightweight youtube embed. Still should feel the same to the user, just MUCH faster to initialize and paint.
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*
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* Thx to these as the inspiration
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* https://storage.googleapis.com/amp-vs-non-amp/youtube-lazy.html
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* https://autoplay-youtube-player.glitch.me/
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*
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* Once built it, I also found these:
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* https://github.com/ampproject/amphtml/blob/master/extensions/amp-youtube (👍👍)
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* https://github.com/Daugilas/lazyYT
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* https://github.com/vb/lazyframe
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*/
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class LiteYTEmbed extends HTMLElement {
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connectedCallback() {
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this.videoId = this.getAttribute('videoid');
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let playBtnEl = this.querySelector('.lty-playbtn');
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// A label for the button takes priority over a [playlabel] attribute on the custom-element
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this.playLabel = (playBtnEl && playBtnEl.textContent.trim()) || this.getAttribute('playlabel') || 'Play';
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this.dataset.title = this.getAttribute('title') || "";
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/**
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* Lo, the youtube poster image! (aka the thumbnail, image placeholder, etc)
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*
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* See https://github.com/paulirish/lite-youtube-embed/blob/master/youtube-thumbnail-urls.md
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*/
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if (!this.style.backgroundImage) {
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this.style.backgroundImage = `url("https://i.ytimg.com/vi/${this.videoId}/hqdefault.jpg")`;
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this.upgradePosterImage();
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}
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// Set up play button, and its visually hidden label
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if (!playBtnEl) {
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playBtnEl = document.createElement('button');
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playBtnEl.type = 'button';
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playBtnEl.classList.add('lty-playbtn');
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this.append(playBtnEl);
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}
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if (!playBtnEl.textContent) {
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const playBtnLabelEl = document.createElement('span');
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playBtnLabelEl.className = 'lyt-visually-hidden';
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playBtnLabelEl.textContent = this.playLabel;
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playBtnEl.append(playBtnLabelEl);
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}
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this.addNoscriptIframe();
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playBtnEl.removeAttribute('href');
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// On hover (or tap), warm up the TCP connections we're (likely) about to use.
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this.addEventListener('pointerover', LiteYTEmbed.warmConnections, {once: true});
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// Once the user clicks, add the real iframe and drop our play button
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// TODO: In the future we could be like amp-youtube and silently swap in the iframe during idle time
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// We'd want to only do this for in-viewport or near-viewport ones: https://github.com/ampproject/amphtml/pull/5003
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this.addEventListener('click', this.activate);
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// Chrome & Edge desktop have no problem with the basic YouTube Embed with ?autoplay=1
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// However Safari desktop and most/all mobile browsers do not successfully track the user gesture of clicking through the creation/loading of the iframe,
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// so they don't autoplay automatically. Instead we must load an additional 2 sequential JS files (1KB + 165KB) (un-br) for the YT Player API
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// TODO: Try loading the the YT API in parallel with our iframe and then attaching/playing it. #82
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this.needsYTApi = this.hasAttribute("js-api") || navigator.vendor.includes('Apple') || navigator.userAgent.includes('Mobi');
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}
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/**
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* Add a <link rel={preload | preconnect} ...> to the head
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*/
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static addPrefetch(kind, url, as) {
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const linkEl = document.createElement('link');
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linkEl.rel = kind;
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linkEl.href = url;
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if (as) {
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linkEl.as = as;
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}
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document.head.append(linkEl);
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}
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/**
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* Begin pre-connecting to warm up the iframe load
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* Since the embed's network requests load within its iframe,
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* preload/prefetch'ing them outside the iframe will only cause double-downloads.
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* So, the best we can do is warm up a few connections to origins that are in the critical path.
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*
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* Maybe `<link rel=preload as=document>` would work, but it's unsupported: http://crbug.com/593267
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* But TBH, I don't think it'll happen soon with Site Isolation and split caches adding serious complexity.
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*/
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static warmConnections() {
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if (LiteYTEmbed.preconnected) return;
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// The iframe document and most of its subresources come right off youtube.com
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LiteYTEmbed.addPrefetch('preconnect', 'https://www.youtube-nocookie.com');
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// The botguard script is fetched off from google.com
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LiteYTEmbed.addPrefetch('preconnect', 'https://www.google.com');
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// Not certain if these ad related domains are in the critical path. Could verify with domain-specific throttling.
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LiteYTEmbed.addPrefetch('preconnect', 'https://googleads.g.doubleclick.net');
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LiteYTEmbed.addPrefetch('preconnect', 'https://static.doubleclick.net');
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LiteYTEmbed.preconnected = true;
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}
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fetchYTPlayerApi() {
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if (window.YT || (window.YT && window.YT.Player)) return;
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this.ytApiPromise = new Promise((res, rej) => {
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var el = document.createElement('script');
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el.src = 'https://www.youtube.com/iframe_api';
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el.async = true;
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el.onload = _ => {
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YT.ready(res);
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};
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el.onerror = rej;
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this.append(el);
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});
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}
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/** Return the YT Player API instance. (Public L-YT-E API) */
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async getYTPlayer() {
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if(!this.playerPromise) {
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await this.activate();
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}
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return this.playerPromise;
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}
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async addYTPlayerIframe() {
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this.fetchYTPlayerApi();
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await this.ytApiPromise;
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const videoPlaceholderEl = document.createElement('div')
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this.append(videoPlaceholderEl);
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const paramsObj = Object.fromEntries(this.getParams().entries());
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this.playerPromise = new Promise(resolve => {
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let player = new YT.Player(videoPlaceholderEl, {
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width: '100%',
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videoId: this.videoId,
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playerVars: paramsObj,
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events: {
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'onReady': event => {
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event.target.playVideo();
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resolve(player);
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}
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}
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});
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});
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}
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// Add the iframe within <noscript> for indexability discoverability. See https://github.com/paulirish/lite-youtube-embed/issues/105
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addNoscriptIframe() {
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const iframeEl = this.createBasicIframe();
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const noscriptEl = document.createElement('noscript');
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// Appending into noscript isn't equivalant for mysterious reasons: https://html.spec.whatwg.org/multipage/scripting.html#the-noscript-element
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noscriptEl.innerHTML = iframeEl.outerHTML;
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this.append(noscriptEl);
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}
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getParams() {
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const params = new URLSearchParams(this.getAttribute('params') || []);
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params.append('autoplay', '1');
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params.append('playsinline', '1');
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return params;
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}
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async activate(){
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if (this.classList.contains('lyt-activated')) return;
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this.classList.add('lyt-activated');
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if (this.needsYTApi) {
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return this.addYTPlayerIframe(this.getParams());
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}
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const iframeEl = this.createBasicIframe();
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this.append(iframeEl);
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// Set focus for a11y
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iframeEl.focus();
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}
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createBasicIframe(){
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const iframeEl = document.createElement('iframe');
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iframeEl.width = 560;
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iframeEl.height = 315;
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// No encoding necessary as [title] is safe. https://cheatsheetseries.owasp.org/cheatsheets/Cross_Site_Scripting_Prevention_Cheat_Sheet.html#:~:text=Safe%20HTML%20Attributes%20include
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iframeEl.title = this.playLabel;
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iframeEl.allow = 'accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture';
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iframeEl.allowFullscreen = true;
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// AFAIK, the encoding here isn't necessary for XSS, but we'll do it only because this is a URL
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// https://stackoverflow.com/q/64959723/89484
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iframeEl.src = `https://www.youtube-nocookie.com/embed/${encodeURIComponent(this.videoId)}?${this.getParams().toString()}`;
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return iframeEl;
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}
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/**
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* In the spirit of the `lowsrc` attribute and progressive JPEGs, we'll upgrade the reliable
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* poster image to a higher resolution one, if it's available.
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* Interestingly this sddefault webp is often smaller in filesize, but we will still attempt it second
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* because getting _an_ image in front of the user if our first priority.
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*
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* See https://github.com/paulirish/lite-youtube-embed/blob/master/youtube-thumbnail-urls.md for more details
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*/
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upgradePosterImage() {
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// Defer to reduce network contention.
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setTimeout(() => {
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const webpUrl = `https://i.ytimg.com/vi_webp/${this.videoId}/sddefault.webp`;
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const img = new Image();
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img.fetchPriority = 'low'; // low priority to reduce network contention
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img.referrerpolicy = 'origin'; // Not 100% sure it's needed, but https://github.com/ampproject/amphtml/pull/3940
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img.src = webpUrl;
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img.onload = e => {
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// A pretty ugly hack since onerror won't fire on YouTube image 404. This is (probably) due to
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// Youtube's style of returning data even with a 404 status. That data is a 120x90 placeholder image.
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// … per "annoying yt 404 behavior" in the .md
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const noAvailablePoster = e.target.naturalHeight == 90 && e.target.naturalWidth == 120;
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if (noAvailablePoster) return;
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this.style.backgroundImage = `url("${webpUrl}")`;
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}
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}, 100);
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}
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}
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// Register custom element
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customElements.define('lite-youtube', LiteYTEmbed);
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