usrspace-browser-addon/background/index.js

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

function fetchCalendar(days = 28) {
	let url = `${Config.calenderUrl}?o=json`;
	if (days) {
		url += `&r=${days}`;
	}
	return fetchJson(url);
}

function fetchSpaceApi() {
	return fetchJson(Config.spaceApiUrl);
}

async function 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});
	}
	try {
		await Promise.all([badgeText, badgeColor]);
	} catch (error) {
		console.error(error);
	}
}

function sendNotification(open) {
	browser.notifications.create('status-change', {
		type: 'basic',
		title: 'Space Status',
		message: `Space ist jetzt ${open ? 'offen' : 'geschlossen'}.`,
		iconUrl: browser.runtime.getURL('icons/favicon.svg')
	});
}

async function fetchNewData() {
	try {
		const json = await fetchCalendar();
		window.calendar = json;
	} catch (error) {
		console.error(error);
	}

	try {
		const json = await fetchSpaceApi();
		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;

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

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