usrspace-browser-addon/background/index.js

const fetchJson = (url) => {
  return fetch(url).then((response) => (response.json()));
};

const fetchCalendar = (days = 28) => {
  let url = Config.calenderUrl + '?o=json';
  if (days) {
    url += '&r=' + days;
  }
  return fetchJson(url);
};

const fetchSpaceApi = () => {
  return fetchJson(Config.spaceApiUrl);
};

const updateBadge = (open) => {
  let badgeText, badgeColor;
  if (open) {
    badgeText = browser.browserAction.setBadgeText({text: 'open'});
    badgeColor = browser.browserAction.setBadgeBackgroundColor({color: Config.openColor});
  } else {
    badgeText = browser.browserAction.setBadgeText({text: ''});
    badgeColor = browser.browserAction.setBadgeBackgroundColor({color: null});
  }
  Promise.all([badgeText, badgeColor])
    .then()
    .catch((error) => {
      console.error(error);
    });
};

const sendNotification = (open) => {
  browser.notifications.create('notification-id', {
    type: 'basic',
    iconUrl: browser.runtime.getURL('icons/logo.svg'),
    title: 'Space Status',
    message: 'Space ist jetzt ' + (open ? 'offen' : 'geschlossen') + '.'
  });
};

const fetchNewData = () => {
  fetchCalendar().then((json) => {
    window.calendar = json;
  }).catch((error) => {
    console.error(error);
  });

  fetchSpaceApi().then((json) => {
    if (window.spaceApi && window.spaceApi.state.open !== json.state.open) {
      sendNotification(json.state.open)
    }
    window.spaceApi = json;
    updateBadge(window.spaceApi.state.open);
  }).catch((error) => {
    console.error(error);
  });
};

let intervalHandler = null;

const stopFetching = () => {
  if (intervalHandler !== null) {
    clearInterval(intervalHandler);
    intervalHandler = null;
  }
};
const startFetching = () => {
  fetchNewData();
  if (intervalHandler === null) {
    intervalHandler = setInterval(() => {
      fetchNewData();
    }, Config.refreshTimeout);
  }
};

window.addEventListener('offline', () => {
  stopFetching();
});
window.addEventListener('online', () => {
  startFetching();
});
if (window.navigator.onLine) {
  startFetching();
}