Progressive web applications (PWAs) are web applications that load like regular web pages or websites but can offer the user functionality such as working offline, push notifications, and device hardware access traditionally available only to nativeapplications. PWAs combine the flexibility of the web with the experience of a native application.
In 2015, designer Frances Berriman and Google Chrome engineer Alex Russell coined the term "progressive web apps"to describe apps taking advantage of new features supported by modern browsers, including service workers and web app manifests, that let users upgrade web apps to progressive web applications in their native operating system (OS). According to Google Developers, these characteristics are:
Progressive web apps are an enhancement of existing web technology. As such, they do not require separate bundling or distribution. Publication of a progressive web app is as it would be for any other web page. PWAs work in any browser, but "app-like" features such as being independent of connectivity, install to home screen & push messaging depend on browser support. As of April 2018, those features are supported to varying degrees by the Microsoft Edge, Google Chrome, Mozilla Firefox and Safari browsers, but more browsers may support the features needed in the future.
The technical baseline criteria for a site to be considered a progressive web app by browsers were described by Russell in a follow-up post:
Commonly used technologies serve to create progressive web apps in the broad sense are the following:
This metadata is crucial for an app to be added to a home screen or otherwise listed alongside native apps.
An earlier technology to support offline use of the web.It works adequately for the use case it was designed for (single-page application), but fails in problematic ways for wikis and other multi-page apps. Currently supported by major browsers and in use for years by some sites, but will eventually be removed.
Native mobile apps deliver rich experiences and high performance, purchased at the expense of storage space, lack of real-time updates, and low search engine visibility. Traditional web apps suffer from the inverse set of factors: lack of a native compiled executable, along with dependence on unreliable and potentially slow web connectivity. Service workers are used in an attempt to give progressive web apps the best of both these worlds.
Technically, service workers provide a scriptable network proxy in the web browser to manage the web/HTTP requests programmatically. The service workers lie between the network and device to supply the content. They are capable of using the cache mechanisms efficiently and allow error-free behavior during offline periods.
Properties of service workers:
Benefits of service workers:
A NoSQL database built into modern browsers Allows a PWA to immediately display content, regardless of connection status or speed.
Key-Value stores that largely make cookies obsolete.
Some progressive web apps use an architectural approach called the App Shell Model. For rapid loading, service workers store the Basic User Interface or "shell" of the responsive web design web application. This shell provides an initial static frame, a layout or architecture into which content can be loaded progressively as well as dynamically, allowing users to engage with the app despite varying degrees of web connectivity. The shell can be stored locally in the browser cache of the mobile device.