Then you have to build that in your application. In typical use-cases, your application does not have to know about Service Workers, but usually not the vice ve

Then you have to build that in your application. In typical use-cases, your application does not have to know about Service Workers, but usually not the vice versa. For example, you can decide to intercept /article/show/{id}, just get the content for the article from your API, compile it with a template you have cached, and serve that instead. From the perspective of your app, nothing has changed. It is the holy grail of progressive enhancement.