React Cookbook

Chapter 11. Progressive Web Applications

Progressive web applications (PWAs) are web applications that try to behave like locally installed applications. They can work offline, integrate with the native notification system, and have the ability to run long background processes, which can continue even after you leave the website. They’re called progressive because they smoothly downgrade their functionality if some feature is not available in the current browser.

This chapter focuses almost exclusively on one feature of PWAs: service workers. You will occasionally encounter the term progressive web application used to describe any JavaScript-rich browser application. The truth is that unless that application uses service workers, it isn’t a PWA.

Service workers are, in effect, a locally installed server for the application. The backend server is a software distribution mechanism and a provider of live data services, but the service worker is really in charge because it provides access to the network. It can choose to satisfy network requests from its own local cache. If the network is not available, it can choose to replace network resources with local placeholders. It can even queue data updates offline and synchronize with the backend server when the network connection reappears.

This is a good topic for the final chapter because it has been the most enjoyable chapter to write. Service workers are one of the most fascinating features found in modern browsers. We hope you have ...