mastodon/public/embed.js

// @ts-check
(function (allowedPrefixes) {
  'use strict';

  /**
   * @param {() => void} loaded
   */
  var ready = function (loaded) {
    if (document.readyState === 'complete') {
      loaded();
    } else {
      document.addEventListener('readystatechange', function () {
        if (document.readyState === 'complete') {
          loaded();
        }
      });
    }
  };

  /**
   * @param {Map} map
   */
  var generateId = function (map) {
    var id = 0,
      failCount = 0,
      idBuffer = new Uint32Array(1);

    while (id === 0 || map.has(id)) {
      id = crypto.getRandomValues(idBuffer)[0];
      failCount++;

      if (failCount > 100) {
        // give up and assign (easily guessable) unique number if getRandomValues is broken or no luck
        id = -(map.size + 1);
        break;
      }
    }

    return id;
  };

  ready(function () {
    /** @type {Map<number, HTMLQuoteElement | HTMLIFrameElement>} */
    var embeds = new Map();

    window.addEventListener('message', function (e) {
      var data = e.data || {};

      if (
        typeof data !== 'object' ||
        data.type !== 'setHeight' ||
        !embeds.has(data.id)
      ) {
        return;
      }

      var embed = embeds.get(data.id);

      if (embed instanceof HTMLIFrameElement) {
        embed.height = data.height;
      }

      if (embed instanceof HTMLQuoteElement) {
        var iframe = embed.querySelector('iframe');

        if (!iframe || ('source' in e && iframe.contentWindow !== e.source)) {
          return;
        }

        iframe.height = data.height;

        var placeholder = embed.querySelector('a');

        if (!placeholder) return;

        embed.removeChild(placeholder);
      }
    });

    // Legacy embeds
    document.querySelectorAll('iframe.mastodon-embed').forEach((iframe) => {
      var id = generateId(embeds);

      embeds.set(id, iframe);

      iframe.allow = 'fullscreen';
      iframe.sandbox = 'allow-scripts allow-same-origin allow-popups';
      iframe.style.border = 0;
      iframe.style.overflow = 'hidden';
      iframe.style.display = 'block';

      iframe.onload = function () {
        iframe.contentWindow.postMessage(
          {
            type: 'setHeight',
            id: id,
          },
          '*',
        );
      };

      iframe.onload(); // In case the script is executing after the iframe has already loaded
    });

    // New generation of embeds
    document
      .querySelectorAll('blockquote.mastodon-embed')
      .forEach((container) => {
        var id = generateId(embeds);

        embeds.set(id, container);

        var iframe = document.createElement('iframe');
        var embedUrl = new URL(container.getAttribute('data-embed-url'));

        if (embedUrl.protocol !== 'https:' && embedUrl.protocol !== 'http:')
          return;
        if (
          allowedPrefixes.every(
            (allowedPrefix) => !embedUrl.toString().startsWith(allowedPrefix),
          )
        )
          return;

        iframe.src = embedUrl.toString();
        iframe.width = container.clientWidth;
        iframe.height = 0;
        iframe.allow = 'fullscreen';
        iframe.sandbox = 'allow-scripts allow-same-origin allow-popups';
        iframe.style.border = 0;
        iframe.style.overflow = 'hidden';
        iframe.style.display = 'block';

        iframe.onload = function () {
          iframe.contentWindow.postMessage(
            {
              type: 'setHeight',
              id: id,
            },
            '*',
          );
        };

        container.appendChild(iframe);
      });
  });
})(
  document.currentScript &&
    document.currentScript.tagName.toUpperCase() === 'SCRIPT' &&
    document.currentScript.dataset.allowedPrefixes
    ? document.currentScript.dataset.allowedPrefixes.split(' ')
    : [],
);