diff --git a/src/index.js b/src/index.js
index 3fdf63b0..af0b4517 100644
--- a/src/index.js
+++ b/src/index.js
@@ -2,7 +2,7 @@ import React from 'react';
 import ReactDOM from 'react-dom';
 import { Router } from 'react-router-dom'
 import App from './components/App/App';
-import registerServiceWorker from './registerServiceWorker';
+import * as serviceWorkerRegistration from './registerServiceWorker';
 import { createBrowserHistory } from 'history';
 
 // We have to import the CSS here. By placing it in index.html like the Bootstrap getting started guide suggests,
@@ -15,4 +15,4 @@ import './index.css'; // where we wish to override bootstrap defaults
 const history = createBrowserHistory();
 
 ReactDOM.render(<Router history={history}><App/></Router>, document.getElementById('root'));
-registerServiceWorker();
+serviceWorkerRegistration.unregister();
diff --git a/src/registerServiceWorker.js b/src/registerServiceWorker.js
index 4a3ccf02..2262ecdb 100644
--- a/src/registerServiceWorker.js
+++ b/src/registerServiceWorker.js
@@ -1,108 +1,137 @@
-// In production, we register a service worker to serve assets from local cache.
+// This optional code is used to register a service worker.
+// register() is not called by default.
 
 // This lets the app load faster on subsequent visits in production, and gives
 // it offline capabilities. However, it also means that developers (and users)
-// will only see deployed updates on the "N+1" visit to a page, since previously
-// cached resources are updated in the background.
+// will only see deployed updates on subsequent visits to a page, after all the
+// existing tabs open on the page have been closed, since previously cached
+// resources are updated in the background.
 
-// To learn more about the benefits of this model, read https://goo.gl/KwvDNy.
-// This link also includes instructions on opting out of this behavior.
+// To learn more about the benefits of this model and instructions on how to
+// opt-in, read https://cra.link/PWA
 
 const isLocalhost = Boolean(
   window.location.hostname === 'localhost' ||
     // [::1] is the IPv6 localhost address.
     window.location.hostname === '[::1]' ||
-    // 127.0.0.1/8 is considered localhost for IPv4.
-    window.location.hostname.match(
-      /^127(?:\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)){3}$/
-    )
+    // 127.0.0.0/8 are considered localhost for IPv4.
+    window.location.hostname.match(/^127(?:\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)){3}$/)
 );
 
-export default function register() {
+export function register(config) {
   if (process.env.NODE_ENV === 'production' && 'serviceWorker' in navigator) {
     // The URL constructor is available in all browsers that support SW.
-    const publicUrl = new URL(process.env.PUBLIC_URL, window.location);
+    const publicUrl = new URL(process.env.PUBLIC_URL, window.location.href);
     if (publicUrl.origin !== window.location.origin) {
       // Our service worker won't work if PUBLIC_URL is on a different origin
       // from what our page is served on. This might happen if a CDN is used to
-      // serve assets; see https://github.com/facebookincubator/create-react-app/issues/2374
+      // serve assets; see https://github.com/facebook/create-react-app/issues/2374
       return;
     }
 
     window.addEventListener('load', () => {
       const swUrl = `${process.env.PUBLIC_URL}/service-worker.js`;
 
-      if (!isLocalhost) {
-        // Is not local host. Just register service worker
-        registerValidSW(swUrl);
+      if (isLocalhost) {
+        // This is running on localhost. Let's check if a service worker still exists or not.
+        checkValidServiceWorker(swUrl, config);
+
+        // Add some additional logging to localhost, pointing developers to the
+        // service worker/PWA documentation.
+        navigator.serviceWorker.ready.then(() => {
+          console.log(
+            'This web app is being served cache-first by a service ' +
+              'worker. To learn more, visit https://cra.link/PWA'
+          );
+        });
       } else {
-        // This is running on localhost. Lets check if a service worker still exists or not.
-        checkValidServiceWorker(swUrl);
+        // Is not localhost. Just register service worker
+        registerValidSW(swUrl, config);
       }
     });
   }
 }
 
-function registerValidSW(swUrl) {
+function registerValidSW(swUrl, config) {
   navigator.serviceWorker
     .register(swUrl)
-    .then(registration => {
+    .then((registration) => {
       registration.onupdatefound = () => {
         const installingWorker = registration.installing;
+        if (installingWorker == null) {
+          return;
+        }
         installingWorker.onstatechange = () => {
           if (installingWorker.state === 'installed') {
             if (navigator.serviceWorker.controller) {
-              // At this point, the old content will have been purged and
-              // the fresh content will have been added to the cache.
-              // It's the perfect time to display a "New content is
-              // available; please refresh." message in your web app.
-              console.log('New content is available; please refresh.');
+              // At this point, the updated precached content has been fetched,
+              // but the previous service worker will still serve the older
+              // content until all client tabs are closed.
+              console.log(
+                'New content is available and will be used when all ' +
+                  'tabs for this page are closed. See https://cra.link/PWA.'
+              );
+
+              // Execute callback
+              if (config && config.onUpdate) {
+                config.onUpdate(registration);
+              }
             } else {
               // At this point, everything has been precached.
               // It's the perfect time to display a
               // "Content is cached for offline use." message.
               console.log('Content is cached for offline use.');
+
+              // Execute callback
+              if (config && config.onSuccess) {
+                config.onSuccess(registration);
+              }
             }
           }
         };
       };
     })
-    .catch(error => {
+    .catch((error) => {
       console.error('Error during service worker registration:', error);
     });
 }
 
-function checkValidServiceWorker(swUrl) {
+function checkValidServiceWorker(swUrl, config) {
   // Check if the service worker can be found. If it can't reload the page.
-  fetch(swUrl)
-    .then(response => {
+  fetch(swUrl, {
+    headers: { 'Service-Worker': 'script' },
+  })
+    .then((response) => {
       // Ensure service worker exists, and that we really are getting a JS file.
+      const contentType = response.headers.get('content-type');
       if (
         response.status === 404 ||
-        response.headers.get('content-type').indexOf('javascript') === -1
+        (contentType != null && contentType.indexOf('javascript') === -1)
       ) {
         // No service worker found. Probably a different app. Reload the page.
-        navigator.serviceWorker.ready.then(registration => {
+        navigator.serviceWorker.ready.then((registration) => {
           registration.unregister().then(() => {
             window.location.reload();
           });
         });
       } else {
         // Service worker found. Proceed as normal.
-        registerValidSW(swUrl);
+        registerValidSW(swUrl, config);
       }
     })
     .catch(() => {
-      console.log(
-        'No internet connection found. App is running in offline mode.'
-      );
+      console.log('No internet connection found. App is running in offline mode.');
     });
 }
 
 export function unregister() {
   if ('serviceWorker' in navigator) {
-    navigator.serviceWorker.ready.then(registration => {
-      registration.unregister();
-    });
+    navigator.serviceWorker.ready
+      .then((registration) => {
+        registration.unregister();
+      })
+      .catch((error) => {
+        console.error(error.message);
+      });
   }
 }