Service Worker

sw.js

// https://developer.mozilla.org/en-US/docs/Web/API/Service_Worker_API/Using_Service_Workers

// app.js
if ('serviceWorker' in navigator) {
  navigator.serviceWorker.register('/sw-test/sw.js', { scope: '/sw-test/' }).then(function(reg) {
    
    if(reg.installing) {
      console.log('Service worker installing');
    } else if(reg.waiting) {
      console.log('Service worker installed');
    } else if(reg.active) {
      console.log('Service worker active');
    }
    
  }).catch(function(error) {
    // registration failed
    console.log('Registration failed with ' + error);
  });
}

// sw.js
this.addEventListener('install', function(event) {
  event.waitUntil(
    caches.open('v1').then(function(cache) {
      return cache.addAll([
        '/sw-test/',
        '/sw-test/index.html',
        '/sw-test/*.css',
        '*.js',
        '/sw-test/assets/*.jpg'
      ]);
    })
  );
});

this.addEventListener('fetch', function(event) {
  var response;
  event.respondWith(caches.match(event.request).catch(function() {
    return fetch(event.request);
  }).then(function(r) {
    response = r;
    caches.open('v1').then(function(cache) {
      cache.put(event.request, response);
    });
    return response.clone();
  }).catch(function() {
    return caches.match('/sw-test/gallery/myLittleVader.jpg');
  }));
});