Simple Service Worker asset caching script - see http://purelywebdesign.co.uk/tutorial/service-worker-caching-tutorial/

serviceWorkerClient.js

'use strict';

var CACHE_NAME = 'psw-cache-v1';
var urlsToCache = [
  '/assets/site-logo.svg',
  '/css/main.css',
  '/javascript/application.js'
];

self.addEventListener('install', function(event) {

	// Open device cache and store our list of items
  event.waitUntil(
    caches.open(CACHE_NAME).then(function(cache) {
      return cache.addAll(urlsToCache);
    })
  );
});

self.addEventListener('fetch', function(event) {
	// Intercept fetch request
  event.respondWith(
  	// match and serve cached asset if it exists
    caches.match(event.request).then(function(response) {
      return response || fetch(event.request);
    })
  );
});

self.addEventListener('activate', function(event) {

  event.waitUntil(
  	// Open our apps cache and delete any old cache items
  	caches.open(CACHE_NAME).then(function(cacheNames){
  		cacheNames.keys().then(function(cache){
  			cache.forEach(function(element, index, array) {
  				if (urlsToCache.indexOf(element) === -1){
  					caches.delete(element);
  				}
  	    });
  		});
  	})
  );
});

serviceWorkerServer.js

$(document).ready(function(){
  'use strict';
  	
	// Check that service workers are available
	if ('serviceWorker' in navigator) {
		console.log('ServiceWorker available in navigator');
		
	  navigator.serviceWorker.register('/serviceWorkerClient.js').then(function(reg) {
	    console.log('ServiceWorker registration successful with scope: ', reg.scope);
	  }).catch(function(err) {
	    console.log('ServiceWorker registration failed: ', err);
	  });
	}
});