Service Worker not working in Angular

add this to main.ts:

platformBrowserDynamic().bootstrapModule(AppModule).then(() => {
  if ('serviceWorker' in navigator && environment.production) {
    navigator.serviceWorker.register('ngsw-worker.js');
  }
}).catch(err => console.log(err));

References
https://stackoverflow.com/questions/48723206/angular-5-service-worker-not-working