Frontend/src/serviceWorker.ts

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}$/)
);

type Config = {
    onSuccess?: (registration: ServiceWorkerRegistration) => void;
    onUpdate?: (registration: ServiceWorkerRegistration) => void;
};

export function register(config?: Config) {
    if(process.env.NODE_ENV === 'production' && 'serviceWorker' in navigator) {
        const publicUrl = new URL(
            (process as { env: { [key: string]: string } }).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(
                        'This web app is being served cache-first by a service ' +
                        'worker. To learn more, visit https://bit.ly/CRA-PWA'
                    );
                });
            } else {
                registerValidSW(swUrl, config);
            }
        });
    }
}

function registerValidSW(swUrl: string, config?: 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(
                                'New content is available and will be used when all ' +
                                'tabs for this page are closed. See https://bit.ly/CRA-PWA.'
                            );

                            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: string, config?: 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();
        });
    }
}