https://www.kamifurano.jp/wp-content/themes/kamifurano/scripts/lite-youtube-embed/src/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('.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          this.style.backgroundImage = `url("https://i.ytimg.com/vi/${this.videoId}/hqdefault.jpg")`;
32        }
33
34        // Set up play button, and its visually hidden label
35        if (!playBtnEl) {
36            playBtnEl = document.createElement('button');
37            playBtnEl.type = 'button';
38            playBtnEl.classList.add('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        // On hover (or tap), warm up the TCP connections we're (likely) about to use.
49        this.addEventListener('pointerover', LiteYTEmbed.warmConnections, {once: true});
50
51        // Once the user clicks, add the real iframe and drop our play button
52        // TODO: In the future we could be like amp-youtube and silently swap in the iframe during idle time
53        //   We'd want to only do this for in-viewport or near-viewport ones: https://github.com/ampproject/amphtml/pull/5003
54        this.addEventListener('click', this.addIframe);
55    }
56
57    // // TODO: Support the the user changing the [videoid] attribute
58    // attributeChangedCallback() {
59    // }
60
61    /**
62     * Add a <link rel={preload | preconnect} ...> to the head
63     */
64    static addPrefetch(kind, url, as) {
65        const linkEl = document.createElement('link');
66        linkEl.rel = kind;
67        linkEl.href = url;
68        if (as) {
69            linkEl.as = as;
70        }
71        document.head.append(linkEl);
72    }
73
74    /**
75     * Begin pre-connecting to warm up the iframe load
76     * Since the embed's network requests load within its iframe,
77     *   preload/prefetch'ing them outside the iframe will only cause double-downloads.
78     * So, the best we can do is warm up a few connections to origins that are in the critical path.
79     *
80     * Maybe `<link rel=preload as=document>` would work, but it's unsupported: http://crbug.com/593267
81     * But TBH, I don't think it'll happen soon with Site Isolation and split caches adding serious complexity.
82     */
83    static warmConnections() {
84        if (LiteYTEmbed.preconnected) return;
85
86        // The iframe document and most of its subresources come right off youtube.com
87        LiteYTEmbed.addPrefetch('preconnect', 'https://www.youtube-nocookie.com');
88        // The botguard script is fetched off from google.com
89        LiteYTEmbed.addPrefetch('preconnect', 'https://www.google.com');
90
91        // Not certain if these ad related domains are in the critical path. Could verify with domain-specific throttling.
92        LiteYTEmbed.addPrefetch('preconnect', 'https://googleads.g.doubleclick.net');
93        LiteYTEmbed.addPrefetch('preconnect', 'https://static.doubleclick.net');
94
95        LiteYTEmbed.preconnected = true;
96    }
97
98    addIframe(e) {
99        if (this.classList.contains('lyt-activated')) return;
100        e.preventDefault();
101        this.classList.add('lyt-activated');
102
103        const params = new URLSearchParams(this.getAttribute('params') || []);
104        params.append('autoplay', '1');
105
106        const iframeEl = document.createElement('iframe');
107        iframeEl.width = 560;
108        iframeEl.height = 315;
109        // No encoding necessary as [title] is safe. https://cheatsheetseries.owasp.org/cheatsheets/Cross_Site_Scripting_Prevention_Cheat_Sheet.html#:~:text=Safe%20HTML%20Attributes%20include
110        iframeEl.title = this.playLabel;
111        iframeEl.allow = 'accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture';
112        iframeEl.allowFullscreen = true;
113        // AFAIK, the encoding here isn't necessary for XSS, but we'll do it only because this is a URL
114        // https://stackoverflow.com/q/64959723/89484
115        iframeEl.src = `https://www.youtube-nocookie.com/embed/${encodeURIComponent(this.videoId)}?${params.toString()}`;
116        this.append(iframeEl);
117
118        // Set focus for a11y

119        iframeEl.focus();
120    }
121}
122// Register custom element
123customElements.define('lite-youtube', LiteYTEmbed);