digitransit-ui/app/util/font-sw.js

/* eslint no-restricted-globals: warn */

const CACHE = 'font-cache-v1';
const FONT_DOMAIN = 'https://cloud.typography.com/';

function fetchAndCache(request, cache) {
  return fetch(request.clone()).then(response => {
    if (response.status < 400) {
      cache.put(request, response.clone());
    }

    return response;
  });
}

self.addEventListener('fetch', event => {
  // Do not cache other than font assets that need click counting on every request.
  if (!event.request.url.startsWith(FONT_DOMAIN)) {
    return;
  }

  event.respondWith(
    caches.open(CACHE).then(cache =>
      cache
        .match(event.request)
        .then(cacheResponse => {
          if (cacheResponse) {
            // Required to fetch the fonts for every page load, we also use this to refresh the cache.
            fetchAndCache(event.request, cache);
            return cacheResponse;
          }
          return fetchAndCache(event.request, cache);
        })
        .catch(error => {
          throw error;
        }),
    ),
  );
});