service-worker.js

// check if the serviceWorker object exists in the navigator object
if ('serviceWorker' in navigator) {

  // attach event listener  on page l aod
  window.addEventListener('load', function() {

    // register serviceWorker withthe [service-worker.js] file
    navigator.serviceWorker.register('/service-worker.js').then(registration => {

      // Registration was successful
      console.log('ServiceWorker registration successful with scope: ', registration.scope);

    }, function(err) {
      // registration failed :(
      console.log('ServiceWorker registration failed: ', err);
    });

  });
}

// install event for the service worker
self.addEventListener('install', e => {

  e.waitUntil(
    caches.open('site-static').then(cache => {
      cache.addAll(['/', '/index.html'])
    })
  )
  
})


self.addEventListener('fetch', e => {
  e.respondWith(
    caches.match(e.request).then(res => {
      return res
    })
  )
})