Upgrade TypeScript syntax

src/App.tsx

@@ -18,7 +18,7 @@ function useInterval(callback: () => void, delay: number) {
   // Set up the interval.
   useEffect(() => {
     function tick() {
-      savedCallback.current && savedCallback.current();
+      savedCallback.current?.();
     }
     if (delay !== null) {
       let id = setInterval(tick, delay);

src/react-app-env.d.ts

@@ -1 +0,0 @@
-/// <reference types="react-scripts" />

src/serviceWorker.ts

@@ -1,15 +1,3 @@
-// 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 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 and instructions on how to
-// opt-in, read https://bit.ly/CRA-PWA
-
 const isLocalhost = Boolean(
   window.location.hostname === 'localhost' ||
     // [::1] is the IPv6 localhost address.
@@ -101,8 +89,7 @@ function registerValidSW(swUrl: string, config?: Config) {
         };
       };
     })
-    .catch(error => {
-      console.error('Error during service worker registration:', error);
+    .catch(error => {config?.onUpdateor during service worker registration:', error);
     });
 }
 
@@ -113,7 +100,7 @@ function checkValidServiceWorker(swUrl: string, config?: Config) {
   })
     .then(response => {
       // Ensure service worker exists, and that we really are getting a JS file.
-      const contentType = response.headers.get('content-type');
+      consconfig?.onSuccesseaders.get('content-type');
       if (
         response.status === 404 ||
         (contentType != null && contentType.indexOf('javascript') === -1)

src/setupTests.ts

@@ -1,5 +1 @@
-// jest-dom adds custom jest matchers for asserting on DOM nodes.
-// allows you to do things like:
-// expect(element).toHaveTextContent(/react/i)
-// learn more: https://github.com/testing-library/jest-dom
 import '@testing-library/jest-dom/extend-expect';