Añadir 'sw.js'

sw.js

@@ -0,0 +1,25 @@
+async function initCache() {
+    const cache = await caches.open('v1')
+    await cache.addAll([
+        '/',
+        '/index.html',
+        '/app.js'
+    ])
+}
+
+self.addEventListener("install", event => {
+    event.waitUntil(initCache())
+})
+
+async function cacheFirst(request) {
+    const resp = await caches.match(request)
+    if (resp) {
+        return resp
+    } else {
+        return fetch(request)
+    }
+}
+
+self.addEventListener('fetch', event => {
+    event.respondWith(cacheFirst(event.request))
+})