upstream-rocketchat/apps/meteor/public/workers/index.js

const HTMLToCache = '/';
const version = 'MSW V0.3';

self.addEventListener('install', (event) => {
	event.waitUntil(
		caches.open(version).then((cache) => {
			cache.add(HTMLToCache).then(self.skipWaiting());
		}),
	);
});

self.addEventListener('activate', (event) => {
	event.waitUntil(
		caches
			.keys()
			.then((cacheNames) =>
				Promise.all(
					cacheNames.map((cacheName) => {
						if (version !== cacheName) return caches.delete(cacheName);
					}),
				),
			)
			.then(self.clients.claim()),
	);
});

self.addEventListener('fetch', (event) => {
	const requestToFetch = event.request.clone();
	event.respondWith(
		caches.match(event.request.clone()).then((cached) => {
			// We don't return cached HTML (except if fetch failed)
			if (cached) {
				const resourceType = cached.headers.get('content-type');
				// We only return non css/js/html cached response e.g images
				if (!hasHash(event.request.url) && !/text\/html/.test(resourceType)) {
					return cached;
				}

				// If the CSS/JS didn't change since it's been cached, return the cached version
				if (hasHash(event.request.url) && hasSameHash(event.request.url, cached.url)) {
					return cached;
				}
			}
			return fetch(requestToFetch)
				.then((response) => {
					const clonedResponse = response.clone();
					const contentType = clonedResponse.headers.get('content-type');

					if (
						!clonedResponse ||
						clonedResponse.status !== 200 ||
						clonedResponse.type !== 'basic' ||
						/\/sockjs\//.test(event.request.url)
					) {
						return response;
					}

					if (/html/.test(contentType)) {
						caches.open(version).then((cache) => cache.put(HTMLToCache, clonedResponse));
					} else {
						// Delete old version of a file
						if (hasHash(event.request.url)) {
							caches.open(version).then((cache) =>
								cache.keys().then((keys) =>
									keys.forEach((asset) => {
										if (new RegExp(removeHash(event.request.url)).test(removeHash(asset.url))) {
											cache.delete(asset);
										}
									}),
								),
							);
						}

						caches.open(version).then((cache) => cache.put(event.request, clonedResponse));
					}
					return response;
				})
				.catch(() => {
					if (hasHash(event.request.url)) return caches.match(event.request.url);
					// If the request URL hasn't been served from cache and isn't sockjs we suppose it's HTML
					else if (!/\/sockjs\//.test(event.request.url)) return caches.match(HTMLToCache);
					// Only for sockjs
					return new Response('No connection to the server', {
						status: 503,
						statusText: 'No connection to the server',
						headers: new Headers({ 'Content-Type': 'text/plain' }),
					});
				});
		}),
	);
});

function removeHash(element) {
	if (typeof element === 'string') return element.split('?hash=')[0];
}

function hasHash(element) {
	if (typeof element === 'string') return /\?hash=.*/.test(element);
}

function hasSameHash(firstUrl, secondUrl) {
	if (typeof firstUrl === 'string' && typeof secondUrl === 'string') {
		return /\?hash=(.*)/.exec(firstUrl)[1] === /\?hash=(.*)/.exec(secondUrl)[1];
	}
}

// Service worker created by Ilan Schemoul alias NitroBAY as a specific Service Worker for Meteor
// Please see https://github.com/NitroBAY/meteor-service-worker for the official project source