privacy-redirect/assets/javascript/persist-invidious-prefs.js

'use strict';

window.browser = window.browser || window.chrome;

function getCookie() {
  let ca = document.cookie.split(';');
  for (let i = 0; i < ca.length; i++) {
    let c = ca[i];
    while (c.charAt(0) == ' ') c = c.substring(1, c.length);
    if (c.indexOf('PREFS=') == 0) {
      return JSON.parse(
        decodeURIComponent(c.substring('PREFS='.length, c.length))
      )
    };
  }
  return {};
}

browser.storage.sync.get(
  ['alwaysProxy', 'videoQuality', 'invidiousDarkMode', 'persistInvidiousPrefs'],
  (result) => {
    if (result.persistInvidiousPrefs) {
      const prefs = getCookie();
      prefs.local = result.alwaysProxy;
      prefs.quality = result.videoQuality;
      prefs.dark_mode = result.invidiousDarkMode;
      document.cookie = `PREFS=${encodeURIComponent(JSON.stringify(prefs))}`;
    }
  }
);