Service worker with cache

sw.js

const cacheId = 'cache-v1';

function fetchAndCache(request, cache) {
	return fetch(request).then(function(response) {
		return cache.put(request, response.clone()).then(function() {
			return response;
		});
	});
}

self.addEventListener('fetch', function(event) {
	// This prevents some weird issue with Chrome DevTools and 'only-if-cached'
	// Fixes issue #385, also ref to:
	// - https://github.com/paulirish/caltrainschedule.io/issues/49
	// - https://bugs.chromium.org/p/chromium/issues/detail?id=823392
	if (event.request.cache === 'only-if-cached' && event.request.mode !== 'same-origin') {
		return;
	}
	
	if (event.request.method !== 'GET') {
		return;
	}

	const url = new URL(event.request.url);

	if (url.protocol !== 'https:') {
		return;
	}
	
	if (url.origin !== location.origin) {
		return;
	}

	event.respondWith(
		caches.open(cacheId).then(function(cache) {
			return cache.match(event.request).then(function(response) {
				if (response) {
					event.waitUntil(
						fetchAndCache(event.request, cache)
					);
					return response;
				}

				return fetchAndCache(event.request, cache);
			});
		})
	);
});