Initial seoul project import

sw.js

@@ -0,0 +1,50 @@
+const CACHE_NAME = 'seoul-shortcuts-v1';
+const CORE_ASSETS = [
+  './',
+  './assets/favicon.svg',
+  './assets/icon-32.png',
+  './assets/icon-192.png',
+  './assets/icon-512.png',
+  './assets/apple-touch-icon.png',
+  './manifest.webmanifest'
+];
+
+self.addEventListener('install', event => {
+  event.waitUntil(
+    caches.open(CACHE_NAME)
+      .then(cache => cache.addAll(CORE_ASSETS))
+      .catch(() => undefined)
+  );
+  self.skipWaiting();
+});
+
+self.addEventListener('activate', event => {
+  event.waitUntil(
+    caches.keys().then(keys => Promise.all(
+      keys.filter(key => key !== CACHE_NAME).map(key => caches.delete(key))
+    ))
+  );
+  self.clients.claim();
+});
+
+self.addEventListener('fetch', event => {
+  if (event.request.method !== 'GET') {
+    return;
+  }
+
+  const url = new URL(event.request.url);
+
+  if (url.origin !== location.origin) {
+    return;
+  }
+
+  event.respondWith(
+    fetch(event.request)
+      .then(response => {
+        const copy = response.clone();
+        caches.open(CACHE_NAME).then(cache => cache.put(event.request, copy));
+        return response;
+      })
+      .catch(() => caches.match(event.request))
+  );
+});