How to add event listeners to create-react-app default sw.js file

Question

I want to use the default service-worker (sw.js) file of Create-React-App module.

sw.js file looks like the following code:

const isLocalhost = Boolean(
  window.location.hostname === 'localhost' ||
    window.location.hostname === '[::1]' ||
    window.location.hostname.match(
      /^127(?:\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)){3}$/
    )
);

export function register(config) {
  if (process.env.NODE_ENV === 'production' && 'serviceWorker' in navigator) {
    console.log('[Service Worker] Service Worker Registered!');
    const publicUrl = new URL(process.env.PUBLIC_URL, window.location.href);
    if (publicUrl.origin !== window.location.origin) {
      return;
    }

    window.addEventListener('load', () => {
      const swUrl = `${process.env.PUBLIC_URL}/service-worker.js`;

      if (isLocalhost) {
        checkValidServiceWorker(swUrl, config);

        navigator.serviceWorker.ready.then(() => {
          console.log(
            'hello'
          );
        });
      } else {
        registerValidSW(swUrl, config);
      }
    });

  }
}

function registerValidSW(swUrl, config) {
  navigator.serviceWorker
    .register(swUrl)
    .then(registration => {
      registration.onupdatefound = () => {
        const installingWorker = registration.installing;
        if (installingWorker == null) {
          return;
        }
        installingWorker.onstatechange = () => {
          if (installingWorker.state === 'installed') {
            if (navigator.serviceWorker.controller) {
              console.log(
                'link'
              );

              if (config && config.onUpdate) {
                config.onUpdate(registration);
              }
            } else {
              console.log('Content is cached for offline use.');

              if (config && config.onSuccess) {
                config.onSuccess(registration);
              }
            }
          }
        };
      };
    })
    .catch(error => {
      console.error('Error during service worker registration:', error);
    });
}

function checkValidServiceWorker(swUrl, config) {
  fetch(swUrl)
    .then(response => {
      const contentType = response.headers.get('content-type');
      if (
        response.status === 404 ||
        (contentType != null && contentType.indexOf('javascript') === -1)
      ) {

        navigator.serviceWorker.ready.then(registration => {
          registration.unregister().then(() => {
            window.location.reload();
          });
        });
      } else {
        registerValidSW(swUrl, config);
      }
    })
    .catch(() => {
      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();
    });
  }
}

What I want is to add some more event listener to this file, I have tried different part of the above code to add listeners but it doesn't work! As an example I added the following, but I don't know where it should be placed to work properly:

window.addEventListener('fetch', (e){
    console.log('[service worker] fetch')
})

The other events are install, activate, beforeinstallprompt and etc.

My main purpose of asking this question is to understand how to add install banner to my react project!

Answer 1

You can not modify the generated service worker file in create-react-app without ejecting.. as a workaround you can create a sw-epilog.js file where you add all the service worker specific code and have a script in the package.json that appends that file to the generated service worker file as mentioned in https://github.com/facebook/create-react-app/issues/5890#issuecomment-450915616

I have a gist to demonstrate this here https://gist.github.com/khaledosman/de3535c8873831153efdf6c10a4b4080 see the last two files

// sw-epilog.js
// Add a listener to receive messages from clients
self.addEventListener('message', function(event) {
  // Force SW upgrade (activation of new installed SW version)
  if ( event.data === 'skipWaiting' ) {
    self.skipWaiting();
  }
});

//package.json
"scripts": {
  "build": "rm -rf build/ && react-scripts build && npm run-script sw-epilog",
  "sw-epilog": "cat src/sw-epilog.js >> build/service-worker.js",
},

for a full implementation you can also see https://github.com/khaledosman/create-react-pwa