https://www.natureforever.org/js/lite-yt-embed.js

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('.lyt-playbtn,.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        this.dataset.title = this.getAttribute('title') || "";
22
23        /**
24         * Lo, the youtube poster image!  (aka the thumbnail, image placeholder, etc)
25         *
26         * See https://github.com/paulirish/lite-youtube-embed/blob/master/youtube-thumbnail-urls.md
27         */
28        if (!this.style.backgroundImage) {
29            this.style.backgroundImage = `url("https://i.ytimg.com/vi/${this.videoId}/hqdefault.jpg")`;
30            this.upgradePosterImage();
31        }
32
33        // Set up play button, and its visually hidden label
34        if (!playBtnEl) {
35            playBtnEl = document.createElement('button');
36            playBtnEl.type = 'button';
37            // Include the mispelled 'lty-' in case it's still being used. https://github.com/paulirish/lite-youtube-embed/issues/65
38            playBtnEl.classList.add('lyt-playbtn', 'lty-playbtn');
39            this.append(playBtnEl);
40        }
41        if (!playBtnEl.textContent) {
42            const playBtnLabelEl = document.createElement('span');
43            playBtnLabelEl.className = 'lyt-visually-hidden';
44            playBtnLabelEl.textContent = this.playLabel;
45            playBtnEl.append(playBtnLabelEl);
46        }
47
48        this.addNoscriptIframe();
49
50        // for the PE pattern, change anchor's semantics to button
51        if (playBtnEl.nodeName === 'A') {
52            playBtnEl.removeAttribute('href');
53            playBtnEl.setAttribute('tabindex', '0');
54            playBtnEl.setAttribute('role', 'button');
55            // fake button needs keyboard help
56            playBtnEl.addEventListener('keydown', e => {
57                if (e.key === 'Enter' || e.key === ' ') {
58                    e.preventDefault();
59                    this.activate();
60                }
61            });
62        }
63
64        // On hover (or tap), warm up the TCP connections we're (likely) about to use.
65        this.addEventListener('pointerover', LiteYTEmbed.warmConnections, { once: true });
66        this.addEventListener('focusin', LiteYTEmbed.warmConnections, { once: true });
67
68        // Once the user clicks, add the real iframe and drop our play button
69        // TODO: In the future we could be like amp-youtube and silently swap in the iframe during idle time
70        //   We'd want to only do this for in-viewport or near-viewport ones: https://github.com/ampproject/amphtml/pull/5003
71        this.addEventListener('click', this.activate);
72
73        // Chrome & Edge desktop have no problem with the basic YouTube Embed with ?autoplay=1
74        // However Safari desktop and most/all mobile browsers do not successfully track the user gesture of clicking through the creation/loading of the iframe,
75        // 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
76        // TODO: Try loading the the YT API in parallel with our iframe and then attaching/playing it. #82
77        this.needsYTApi = this.hasAttribute("js-api") || navigator.vendor.includes('Apple') || navigator.userAgent.includes('Mobi');
78    }
79
80    /**
81     * Add a <link rel={preload | preconnect} ...> to the head
82     */
83    static addPrefetch(kind, url, as) {
84        const linkEl = document.createElement('link');
85        linkEl.rel = kind;
86        linkEl.href = url;
87        if (as) {
88            linkEl.as = as;
89        }
90        document.head.append(linkEl);
91    }
92
93    /**
94     * Begin pre-connecting to warm up the iframe load
95     * Since the embed's network requests load within its iframe,
96     *   preload/prefetch'ing them outside the iframe will only cause double-downloads.
97     * So, the best we can do is warm up a few connections to origins that are in the critical path.
98     *
99     * Maybe `<link rel=preload as=document>` would work, but it's unsupported: http://crbug.com/593267
100     * But TBH, I don't think it'll happen soon with Site Isolation and split caches adding serious complexity.
101     */
102    static warmConnections() {
103        if (LiteYTEmbed.preconnected) return;
104
105        // The iframe document and most of its subresources come right off youtube.com
106        LiteYTEmbed.addPrefetch('preconnect', 'https://www.youtube-nocookie.com');
107        // The botguard script is fetched off from google.com
108        LiteYTEmbed.addPrefetch('preconnect', 'https://www.google.com');
109
110        // Not certain if these ad related domains are in the critical path. Could verify with domain-specific throttling.
111        LiteYTEmbed.addPrefetch('preconnect', 'https://googleads.g.doubleclick.net');
112        LiteYTEmbed.addPrefetch('preconnect', 'https://static.doubleclick.net');
113
114        LiteYTEmbed.preconnected = true;
115    }
116
117    fetchYTPlayerApi() {
118        if (window.YT || (window.YT && window.YT.Player)) return;
119
120        this.ytApiPromise = new Promise((res, rej) => {
121            var el = document.createElement('script');
122            el.src = 'https://www.youtube.com/iframe_api';
123            el.async = true;
124            el.onload = _ => {
125                YT.ready(res);
126            };
127            el.onerror = rej;
128            this.append(el);
129        });
130    }
131
132    /** Return the YT Player API instance. (Public L-YT-E API) */
133    async getYTPlayer() {
134        if (!this.playerPromise) {
135            await this.activate();
136        }
137
138        return this.playerPromise;
139    }
140
141    async addYTPlayerIframe() {
142        this.fetchYTPlayerApi();
143        await this.ytApiPromise;
144
145        const videoPlaceholderEl = document.createElement('div')
146        this.append(videoPlaceholderEl);
147
148        const paramsObj = Object.fromEntries(this.getParams().entries());
149
150        this.playerPromise = new Promise(resolve => {
151            let player = new YT.Player(videoPlaceholderEl, {
152                width: '100%',
153                videoId: this.videoId,
154                playerVars: paramsObj,
155                events: {
156                    'onReady': event => {
157                        event.target.playVideo();
158                        resolve(player);
159                    }
160                }
161            });
162        });
163    }
164
165    // Add the iframe within <noscript> for indexability discoverability. See https://github.com/paulirish/lite-youtube-embed/issues/105
166    addNoscriptIframe() {
167        const iframeEl = this.createBasicIframe();
168        const noscriptEl = document.createElement('noscript');
169        // Appending into noscript isn't equivalant for mysterious reasons: https://html.spec.whatwg.org/multipage/scripting.html#the-noscript-element
170        noscriptEl.innerHTML = iframeEl.outerHTML;
171        this.append(noscriptEl);
172    }
173
174    getParams() {
175        const params = new URLSearchParams(this.getAttribute('params') || []);
176        params.append('autoplay', '1');
177        params.append('playsinline', '1');
178        return params;
179    }
180
181    async activate() {
182        if (this.classList.contains('lyt-activated')) return;
183        this.classList.add('lyt-activated');
184
185        if (this.needsYTApi) {
186            return this.addYTPlayerIframe(this.getParams());
187        }
188
189        const iframeEl = this.createBasicIframe();
190        this.append(iframeEl);
191
192        // Set focus for a11y

193        iframeEl.focus();
194    }
195
196    createBasicIframe() {
197        const iframeEl = document.createElement('iframe');
198        iframeEl.width = 560;
199        iframeEl.height = 315;
200        // No encoding necessary as [title] is safe. https://cheatsheetseries.owasp.org/cheatsheets/Cross_Site_Scripting_Prevention_Cheat_Sheet.html#:~:text=Safe%20HTML%20Attributes%20include
201        iframeEl.title = this.playLabel;
202        iframeEl.allow = 'accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture';
203        iframeEl.allowFullscreen = true;
204        // AFAIK, the encoding here isn't necessary for XSS, but we'll do it only because this is a URL
205        // https://stackoverflow.com/q/64959723/89484
206        iframeEl.src = `https://www.youtube-nocookie.com/embed/${encodeURIComponent(this.videoId)}?${this.getParams().toString()}`;
207        return iframeEl;
208    }
209
210    /**
211     * In the spirit of the `lowsrc` attribute and progressive JPEGs, we'll upgrade the reliable
212     * poster image to a higher resolution one, if it's available.
213     * Interestingly this sddefault webp is often smaller in filesize, but we will still attempt it second
214     * because getting _an_ image in front of the user if our first priority.
215     *
216     * See https://github.com/paulirish/lite-youtube-embed/blob/master/youtube-thumbnail-urls.md for more details
217     */
218    upgradePosterImage() {
219        // Defer to reduce network contention.
220        setTimeout(() => {
221            const webpUrl = `https://i.ytimg.com/vi_webp/${this.videoId}/sddefault.webp`;
222            const img = new Image();
223            img.fetchPriority = 'low'; // low priority to reduce network contention
224            img.referrerpolicy = 'origin'; // Not 100% sure it's needed, but https://github.com/ampproject/amphtml/pull/3940
225            img.src = webpUrl;
226            img.onload = e => {
227                // A pretty ugly hack since onerror won't fire on YouTube image 404. This is (probably) due to
228                // Youtube's style of returning data even with a 404 status. That data is a 120x90 placeholder image.
229                // … per "annoying yt 404 behavior" in the .md
230                const noAvailablePoster = e.target.naturalHeight == 90 && e.target.naturalWidth == 120;
231                if (noAvailablePoster) return;
232
233                this.style.backgroundImage = `url("${webpUrl}")`;
234            }
235        }, 100);
236    }
237}
238// Register custom element
239customElements.define('lite-youtube', LiteYTEmbed);