create-react-app: Error: Service worker has an unsupported MIME type ('text/html')

Describe the bug

Using the create-react-app-typescript-pwa template to generate a progressive web app returns the following error when `serviceWorker.register() is called:

index.js:1 Error during service worker registration: DOMException: Failed to register a ServiceWorker for scope ('http://localhost:3000/') with script ('http://localhost:3000/serviceWorker.js'): The script has an unsupported MIME type ('text/html').

• I’m only able to see the error message after I remove the following condition in the checkValidServiceWorker() function in ./src/serviceWorkerRegistration.ts:

if (
        response.status === 404 ||
        (contentType != null && contentType.indexOf('javascript') === -1)
      ) {

Did you try recovering your dependencies?

Yes

Please paste the output of npm --version and/or yarn --version to confirm. –>

7.6.1

Which terms did you search for in User Guide?

PWA, TypeScript, Workbox, Service worker

Environment

current version of create-react-app: 4.0.3 System: OS: Windows 10 10.0.17763

Steps to reproduce

• Run npx create-react-app my-app --template cra-template-pwa-typescript
• modify serviceWorker.unregister() to serviceWorker.register()

Expected behavior

• Service worker should be registered

Actual behavior

Service worker not registered