In Chapter 1, Introduction to Progressive Web Apps, you read about how the web has fallen short in the mobile era and why progressive web applications can level your website to equal or even better capabilities than native options. Service workers are the most important part of a progressive web application because they are the application's backbone.
The web manifest and the home screen icon enhance the ability to develop a relationship with the customer and control the launch experience. Service workers enable a programmatic user experience enhancement when a page is loaded and even when it isn't.
Service workers sit between the browser and the network and act as a proxy server. They provide more than just a caching layer; they are an extensible backbone:
For the coder, service workers are...