Progressive Web app aspect
https://ionicframework.com/pwa
step by step guide, very clear: https://medium.com/@nsmirnova/creating-pwa-with-angular-5-part-2-progressifying-the-application-449e3a706129
Used with this repo
https://www.joshmorony.com/create-a-pwa-with-angular-service-workers-in-ionic-4/