https://adam-mcdaniel.github.io/sage-website/lib/lite-youtube-embe…7b98bd9de51b14dd9988c60e4c89630433292084.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('.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            playBtnEl.classList.add('lty-playbtn');
38            this.append(playBtnEl);
39        }
40        if (!playBtnEl.textContent) {
41            const playBtnLabelEl = document.createElement('span');
42            playBtnLabelEl.className = 'lyt-visually-hidden';
43            playBtnLabelEl.textContent = this.playLabel;
44            playBtnEl.append(playBtnLabelEl);
45        }
46
47        this.addNoscriptIframe();
48
49        // for the PE pattern, change anchor's semantics to button
50        if(playBtnEl.nodeName === 'A'){
51            playBtnEl.removeAttribute('href');
52            playBtnEl.setAttribute('tabindex', '0');
53            playBtnEl.setAttribute('role', 'button');
54            // fake button needs keyboard help
55            playBtnEl.addEventListener('keydown', e => {
56                if( e.key === 'Enter' || e.key === ' ' ){
57                    e.preventDefault();
58                    this.activate();
59                }
60            });
61        }
62
63        // On hover (or tap), warm up the TCP connections we're (likely) about to use.
64        this.addEventListener('pointerover', LiteYTEmbed.warmConnections, {once: true});
65        this.addEventListener('focusin', LiteYTEmbed.warmConnections, {once: true});
66
67        // Once the user clicks, add the real iframe and drop our play button
68        // TODO: In the future we could be like amp-youtube and silently swap in the iframe during idle time
69        //   We'd want to only do this for in-viewport or near-viewport ones: https://github.com/ampproject/amphtml/pull/5003
70        this.addEventListener('click', this.activate);
71
72        // Chrome & Edge desktop have no problem with the basic YouTube Embed with ?autoplay=1
73        // However Safari desktop and most/all mobile browsers do not successfully track the user gesture of clicking through the creation/loading of the iframe,
74        // 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
75        // TODO: Try loading the the YT API in parallel with our iframe and then attaching/playing it. #82
76        this.needsYTApi = this.hasAttribute("js-api") || navigator.vendor.includes('Apple') || navigator.userAgent.includes('Mobi');
77    }
78
79    /**
80     * Add a <link rel={preload | preconnect} ...> to the head
81     */
82    static addPrefetch(kind, url, as) {
83        const linkEl = document.createElement('link');
84        linkEl.rel = kind;
85        linkEl.href = url;
86        if (as) {
87            linkEl.as = as;
88        }
89        document.head.append(linkEl);
90    }
91
92    /**
93     * Begin pre-connecting to warm up the iframe load
94     * Since the embed's network requests load within its iframe,
95     *   preload/prefetch'ing them outside the iframe will only cause double-downloads.
96     * So, the best we can do is warm up a few connections to origins that are in the critical path.
97     *
98     * Maybe `<link rel=preload as=document>` would work, but it's unsupported: http://crbug.com/593267
99     * But TBH, I don't think it'll happen soon with Site Isolation and split caches adding serious complexity.
100     */
101    static warmConnections() {
102        if (LiteYTEmbed.preconnected) return;
103
104        // The iframe document and most of its subresources come right off youtube.com
105        LiteYTEmbed.addPrefetch('preconnect', 'https://www.youtube-nocookie.com');
106        // The botguard script is fetched off from google.com
107        LiteYTEmbed.addPrefetch('preconnect', 'https://www.google.com');
108
109        // Not certain if these ad related domains are in the critical path. Could verify with domain-specific throttling.
110        LiteYTEmbed.addPrefetch('preconnect', 'https://googleads.g.doubleclick.net');
111        LiteYTEmbed.addPrefetch('preconnect', 'https://static.doubleclick.net');
112
113        LiteYTEmbed.preconnected = true;
114    }
115
116    fetchYTPlayerApi() {
117        if (window.YT || (window.YT && window.YT.Player)) return;
118
119        this.ytApiPromise = new Promise((res, rej) => {
120            var el = document.createElement('script');
121            el.src = 'https://www.youtube.com/iframe_api';
122            el.async = true;
123            el.onload = _ => {
124                YT.ready(res);
125            };
126            el.onerror = rej;
127            this.append(el);
128        });
129    }
130
131    /** Return the YT Player API instance. (Public L-YT-E API) */
132    async getYTPlayer() {
133        if(!this.playerPromise) {
134            await this.activate();
135        }
136
137        return this.playerPromise;
138    }
139
140    async addYTPlayerIframe() {
141        this.fetchYTPlayerApi();
142        await this.ytApiPromise;
143
144        const videoPlaceholderEl = document.createElement('div')
145        this.append(videoPlaceholderEl);
146
147        const paramsObj = Object.fromEntries(this.getParams().entries());
148
149        this.playerPromise = new Promise(resolve => {
150            let player = new YT.Player(videoPlaceholderEl, {
151                width: '100%',
152                videoId: this.videoId,
153                playerVars: paramsObj,
154                events: {
155                    'onReady': event => {
156                        event.target.playVideo();
157                        resolve(player);
158                    }
159                }
160            });
161        });
162    }
163
164    // Add the iframe within <noscript> for indexability discoverability. See https://github.com/paulirish/lite-youtube-embed/issues/105
165    addNoscriptIframe() {
166        const iframeEl = this.createBasicIframe();
167        const noscriptEl = document.createElement('noscript');
168        // Appending into noscript isn't equivalant for mysterious reasons: https://html.spec.whatwg.org/multipage/scripting.html#the-noscript-element
169        noscriptEl.innerHTML = iframeEl.outerHTML;
170        this.append(noscriptEl);
171    }
172
173    getParams() {
174        const params = new URLSearchParams(this.getAttribute('params') || []);
175        params.append('autoplay', '1');
176        params.append('playsinline', '1');
177        return params;
178    }
179
180    async activate(){
181        if (this.classList.contains('lyt-activated')) return;
182        this.classList.add('lyt-activated');
183
184        if (this.needsYTApi) {
185            return this.addYTPlayerIframe(this.getParams());
186        }
187
188        const iframeEl = this.createBasicIframe();
189        this.append(iframeEl);
190
191        // Set focus for a11y

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