https://www.asental.eu/script/plugin/lite_youtube.js?v=1771408748

1/**
2 * A lightweight youtube embed. Still should feel the same to the user, just MUCH faster to initialize and paint.
3 *
4 * Thx to these as the inspiration
5 *   https://storage.googleapis.com/amp-vs-non-amp/youtube-lazy.html
6 *   https://autoplay-youtube-player.glitch.me/
7 *
8 * Once built it, I also found these:
9 *   https://github.com/ampproject/amphtml/blob/master/extensions/amp-youtube (👍👍)
10 *   https://github.com/Daugilas/lazyYT
11 *   https://github.com/vb/lazyframe
12 */
13class LiteYTEmbed extends HTMLElement {
14    connectedCallback() {
15        this.videoId = this.getAttribute('videoid');
16
17        let playBtnEl = this.querySelector('.lty-playbtn');
18        // A label for the button takes priority over a [playlabel] attribute on the custom-element
19        this.playLabel = (playBtnEl && playBtnEl.textContent.trim()) || this.getAttribute('playlabel') || 'Play';
20
21        /**
22         * Lo, the youtube placeholder image!  (aka the thumbnail, poster image, etc)
23         *
24         * See https://github.com/paulirish/lite-youtube-embed/blob/master/youtube-thumbnail-urls.md
25         *
26         * TODO: Do the sddefault->hqdefault fallback
27         *       - When doing this, apply referrerpolicy (https://github.com/ampproject/amphtml/pull/3940)
28         * TODO: Consider using webp if supported, falling back to jpg
29         */
30        if (!this.style.backgroundImage) {
31            const videoId = this.videoId;
32            const target = this;
33
34            const urls = [
35                `https://i.ytimg.com/vi/${videoId}/maxresdefault.jpg`,
36                `https://i.ytimg.com/vi/${videoId}/sddefault.jpg`,
37                `https://i.ytimg.com/vi/${videoId}/hqdefault.jpg`
38            ];
39
40            const tryLoad = (index) => {
41                if (index >= urls.length) return;
42
43                const img = new Image();
44
45                img.onload = function() {
46                    if (this.width === 120 && this.height === 90 && index < urls.length - 1) {
47                        tryLoad(index + 1);
48                    } else {
49                        target.style.backgroundImage = `url("${urls[index]}")`;
50                    }
51                };
52
53                img.onerror = function() {
54                    tryLoad(index + 1);
55                };
56
57                img.src = urls[index];
58            };
59
60            tryLoad(0);
61        }
62
63        // Set up play button, and its visually hidden label
64        if (!playBtnEl) {
65            playBtnEl = document.createElement('button');
66            playBtnEl.type = 'button';
67            playBtnEl.classList.add('lty-playbtn');
68            this.append(playBtnEl);
69        }
70        if (!playBtnEl.textContent) {
71            const playBtnLabelEl = document.createElement('span');
72            playBtnLabelEl.className = 'lyt-visually-hidden';
73            playBtnLabelEl.textContent = this.playLabel;
74            playBtnEl.append(playBtnLabelEl);
75        }
76        playBtnEl.removeAttribute('href');
77
78        // On hover (or tap), warm up the TCP connections we're (likely) about to use.
79        this.addEventListener('pointerover', LiteYTEmbed.warmConnections, {once: true});
80
81        // Once the user clicks, add the real iframe and drop our play button
82        // TODO: In the future we could be like amp-youtube and silently swap in the iframe during idle time
83        //   We'd want to only do this for in-viewport or near-viewport ones: https://github.com/ampproject/amphtml/pull/5003
84        this.addEventListener('click', this.addIframe);
85
86        // Chrome & Edge desktop have no problem with the basic YouTube Embed with ?autoplay=1
87        // However Safari desktop and most/all mobile browsers do not successfully track the user gesture of clicking through the creation/loading of the iframe,
88        // 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
89        // TODO: Try loading the the YT API in parallel with our iframe and then attaching/playing it. #82
90        this.needsYTApiForAutoplay = navigator.vendor.includes('Apple') || navigator.userAgent.includes('Mobi');
91    }
92
93    /**
94     * Add a <link rel={preload | preconnect} ...> to the head
95     */
96    static addPrefetch(kind, url, as) {
97        const linkEl = document.createElement('link');
98        linkEl.rel = kind;
99        linkEl.href = url;
100        if (as) {
101            linkEl.as = as;
102        }
103        document.head.append(linkEl);
104    }
105
106    /**
107     * Begin pre-connecting to warm up the iframe load
108     * Since the embed's network requests load within its iframe,
109     *   preload/prefetch'ing them outside the iframe will only cause double-downloads.
110     * So, the best we can do is warm up a few connections to origins that are in the critical path.
111     *
112     * Maybe `<link rel=preload as=document>` would work, but it's unsupported: http://crbug.com/593267
113     * But TBH, I don't think it'll happen soon with Site Isolation and split caches adding serious complexity.
114     */
115    static warmConnections() {
116        if (LiteYTEmbed.preconnected) return;
117
118        // The iframe document and most of its subresources come right off youtube.com
119        LiteYTEmbed.addPrefetch('preconnect', 'https://www.youtube-nocookie.com');
120        // The botguard script is fetched off from google.com
121        LiteYTEmbed.addPrefetch('preconnect', 'https://www.google.com');
122
123        // Not certain if these ad related domains are in the critical path. Could verify with domain-specific throttling.
124        LiteYTEmbed.addPrefetch('preconnect', 'https://googleads.g.doubleclick.net');
125        LiteYTEmbed.addPrefetch('preconnect', 'https://static.doubleclick.net');
126
127        LiteYTEmbed.preconnected = true;
128    }
129
130    fetchYTPlayerApi() {
131        if (window.YT || (window.YT && window.YT.Player)) return;
132
133        this.ytApiPromise = new Promise((res, rej) => {
134            var el = document.createElement('script');
135            el.src = 'https://www.youtube.com/iframe_api';
136            el.async = true;
137            el.onload = _ => {
138                YT.ready(res);
139            };
140            el.onerror = rej;
141            this.append(el);
142        });
143    }
144
145    async addYTPlayerIframe(params) {
146        this.fetchYTPlayerApi();
147        await this.ytApiPromise;
148
149        const videoPlaceholderEl = document.createElement('div')
150        this.append(videoPlaceholderEl);
151

152        const paramsObj = Object.fromEntries(params.entries());
153
154        new YT.Player(videoPlaceholderEl, {
155            width: '100%',
156            videoId: this.videoId,
157            playerVars: paramsObj,
158            events: {
159                'onReady': event => {
160                    event.target.playVideo();
161                }
162            }
163        });
164    }
165
166    async addIframe(){
167        if (this.classList.contains('lyt-activated')) return;
168        this.classList.add('lyt-activated');
169
170        const params = new URLSearchParams(this.getAttribute('params') || []);
171        params.append('autoplay', '1');
172        params.append('playsinline', '1');
173
174        if (this.needsYTApiForAutoplay) {
175            return this.addYTPlayerIframe(params);
176        }
177
178        const iframeEl = document.createElement('iframe');
179        iframeEl.width = 560;
180        iframeEl.height = 315;
181        // No encoding necessary as [title] is safe. https://cheatsheetseries.owasp.org/cheatsheets/Cross_Site_Scripting_Prevention_Cheat_Sheet.html#:~:text=Safe%20HTML%20Attributes%20include
182        iframeEl.title = this.playLabel;
183        iframeEl.allow = 'accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture';
184        iframeEl.allowFullscreen = true;
185        // AFAIK, the encoding here isn't necessary for XSS, but we'll do it only because this is a URL
186        // https://stackoverflow.com/q/64959723/89484
187        iframeEl.src = `https://www.youtube-nocookie.com/embed/${encodeURIComponent(this.videoId)}?${params.toString()}`;
188        this.append(iframeEl);
189
190        // Set focus for a11y
191        iframeEl.focus();
192    }
193}
194// Register custom element
195customElements.define('lite-youtube', LiteYTEmbed);