Progressive Web App (PWA)

1. Is a web app that uses modern web capabilities to deliver an app-like experience to users.
2. succeed when bringing new capabilities while maintaining shared principles:

URLs and links as the core organizing system: if you can't link to it, it isn't part of the web

Markup and styling for accessibility, both to humans and search engines

UI Richness and system capabilities provided as additions to a functional core

Free to implement without permission or payment, which in practice means standards-based

3. New class of applications: To be considered a Progressive Web App, requirements are

deployed to servers
accessible through URLs
indexed by search engines
Progressive	Work for every user, regardless of browser choice, because they are built with progressive enhancement as a core tenet.
Responsive	Fit any form factor, desktop, mobile, tablet, or whatever is next.
Connectivity independent	Enhanced with service workers to work offline or on low quality networks.
App-like	Use the app-shell model to provide app-style navigation and interactions.
Fresh	Always up-to-date.
Safe	Served via HTTPS to prevent snooping and ensure content has not been tampered with.
Discoverable	Are identifiable as “applications” thanks to W3C manifests and service worker registration scope allowing search engines to find them.
Re-engageable	Make re-engagement easy through features like push notifications.
Installable	Allow users to “keep” apps they find most useful on their home screen without the hassle of an app store.
Linkable	Easily share via URL and not require complex installation.

4. These apps aren't packaged and deployed through stores, they're just websites, they progressively become "apps".
5. What Progressive Apps Look Like: 

2014 Chrome Dev Summit site  as an example, we can see the whole flow in action (ht: Paul Kinlan) 

1	The site begins life as a regular tab.
2	The second (or third or fourth) time one visits the site : roughly at the point where the browser it sure it's something you use frequently : a prompt is shown by the browser (populated from the Manifest details)
3	Users can decide to keep apps to the home screen or app launcher
4	When launched from the home screen, these apps blend into their environment : they're top-level, full-screen, and work offline (Of course, they worked offline after step 1), : but now the implicit contract of "appyness" makes that clear.

 

---

https://ionicframework.com/docs/core-concepts/what-are-progressive-web-apps

https://infrequently.org/2015/06/progressive-apps-escaping-tabs-without-losing-our-soul/

(didn't read yet) https://addyosmani.com/blog/getting-started-with-progressive-web-apps/