Added an unregister method, too, just in case.

packages/react-scripts/template/src/index.js

@@ -1,12 +1,12 @@
 import React from 'react';
 import ReactDOM from 'react-dom';
 import App from './App';
-import registerServiceWorker from './register-service-worker';
+import * as serviceWorkerRegistration from './service-worker-registration';
 import './index.css';
 
 ReactDOM.render(
   <App />,
   document.getElementById('root')
 );
 
-registerServiceWorker();
+serviceWorkerRegistration.register();

packages/react-scripts/template/src/register-service-worker.js → packages/react-scripts/template/src/service-worker-registration.js

@@ -1,4 +1,4 @@
-export default () => {
+export function register() {
   if (process.env.NODE_ENV === 'production' && 'serviceWorker' in navigator) {
     window.addEventListener('load', () => {
       const swUrl = `${process.env.PUBLIC_URL}/service-worker.js`;
@@ -27,4 +27,12 @@ export default () => {
       });
     });
   }
-};
+}
+
+export function unregister() {
+  if ('serviceWorker' in navigator) {
+    navigator.serviceWorker.ready.then(function(registration) {
+      registration.unregister();
+    });
+  }
+}