What a PWA is
A progressive web app is a web app that can install, work offline, and behave like a native app, powered mainly by a service worker.
- A service worker is a background script that intercepts network requests.
- It caches assets so the app loads without a connection.
- A web app manifest lets the app be installed to the home screen.
How the service worker intervenes
The service worker sits between the page and the network, serving from cache or fetching as needed.
Core capabilities
- Offline first strategies serve cached content then update in the background.
- Background sync defers actions until connectivity returns.
- Push notifications re engage users even when the tab is closed.
Practical notes
- Version your caches and clean old ones on activation.
- Choose a strategy per resource, such as cache first for assets and network first for data.
- Test update flows so users do not get stuck on a stale service worker.
Key idea
A PWA uses a service worker to cache assets and intercept requests, giving installable offline capable experiences from ordinary web technology.