service worker, attempt 1

sw.js

@@ -0,0 +1,91 @@
+const currentVersion = 'v1';
+
+const addResourcesToCache = async (resources) => {
+    const cache = await caches.open(currentVersion);
+    await cache.addAll(resources);
+};
+
+const putInCache = async (request, response) => {
+    const cache = await caches.open(currentVersion);
+    await cache.put(request, response);
+};
+
+const cacheFirst = async ({ request, preloadResponsePromise }) => {
+    // First try to get the resource from the cache
+    const responseFromCache = await caches.match(request);
+    if (responseFromCache) {
+        return responseFromCache;
+    }
+
+    // Next try to use the preloaded response, if it's there
+    const preloadResponse = await preloadResponsePromise;
+    if (preloadResponse) {
+        console.info('using preload response', preloadResponse);
+        putInCache(request, preloadResponse.clone());
+        return preloadResponse;
+    }
+
+    // Next try to get the resource from the network
+    try {
+        const responseFromNetwork = await fetch(request);
+        // response may be used only once
+        // we need to save clone to put one copy in cache
+        // and serve second one
+        putInCache(request, responseFromNetwork.clone());
+        return responseFromNetwork;
+    } catch (error) {
+        return new Response('Network error happened', {
+            status: 408,
+            headers: { 'Content-Type': 'text/plain' },
+        });
+    }
+};
+
+const deleteCache = async key => {
+    await caches.delete(key)
+}
+
+const deleteOldCaches = async () => {
+    const cacheKeepList = [currentVersion];
+    const keyList = await caches.keys()
+    const cachesToDelete = keyList.filter(key => !cacheKeepList.includes(key))
+    await Promise.all(cachesToDelete.map(deleteCache));
+}
+
+self.addEventListener('activate', (event) => {
+    event.waitUntil(deleteOldCaches());
+});
+
+const enableNavigationPreload = async () => {
+    if (self.registration.navigationPreload) {
+        // Enable navigation preloads!
+        await self.registration.navigationPreload.enable();
+    }
+};
+
+self.addEventListener('activate', (event) => {
+    event.waitUntil(enableNavigationPreload());
+});
+
+self.addEventListener('install', (event) => {
+    event.waitUntil(
+        addResourcesToCache([
+            './heonian-resources/wordlist.json',
+            './heonian-ime/ime.js',
+            './font.otf',
+            './index.html',
+            './main.css',
+            './main.js',
+            './manifest.json'
+        ])
+    );
+});
+
+self.addEventListener('fetch', (event) => {
+    event.respondWith(
+        cacheFirst({
+            request: event.request,
+            preloadResponsePromise: event.preloadResponse
+        })
+    );
+});