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A Progressive Web Application, often abbreviated PWA, is a website that can be installed on a mobile device. The underlying technology is independent from the mobile application stores, uses web technologies and can be relatively light on space and resources. PWAs are real web applications, it is not a hybrid concept. While the concept has been around for a while, Google coined the term and advocated for its support on mobile platforms.
Any site can become a PWA with a Service worker and a Manifest. This technology brings multiple advantages: offline modes, similarity to mobile applications, ease of development, push notifications, etc.
Firebase is a realtime database service that looks similar to a giant JSON file. It has been acquired by Google and specialized for many purposes: application crash reports, Machine Learning, Website hosting, etc. Firebase comes bundled with a Command Line Interface that gets teams started faster with
firebase init and to deploy faster with
Firebase Firestore relies on two concepts: Collections and Documents. A collection may contain a large number of Documents. Documents may reference one or more Collections. Documents must be as small as possible to avoid performance degradation.
To create a Document, you can follow either of these steps:
With the API, it is possible to watch for changes using
onSnapshot. This could be used to add Publish / Subscribe features by specifically requesting recently modified Documents in a Collection. Moreover, Firebase supports ACID transactions, SQL-like requests and Indexes. It is not recommended to use WHERE in realtime applications as the syntax is not powerful and may cause inefficiencies.
Side note: there is a plugin for VueJS that adds offline capabilities to applications. Similarly, adding major OpenID providers is as simple thanks to related modules that link them to Firestore PWAs. Such integrations will link accounts to user IDs which can be then used to limit access to a Document or a Collection, for instance.
To reduce the network usage for a mobile device, it is possible to setup a cache and define cache strategies with Firebase Firestore. The different cache strategies are:
If a user is offline, their messages are queued up before being sent in bulk after the client reconnected to the network.
PWAs being supported by Google, they do not expose much limits on Android. That said, the story is different on iOS; the access to the Notifications API is reduced, changing the icon is impossible unless the application is reinstalled, application state persistence is not perfect. Until very recently, users that switched to an open PWA had to come back to the splash screen every time even though this fix caused other subsequent issues. Finally, there is no hardware access with Google Chrome. This is not true with Safari, though, since its runtime is different.
Firestore is not adapted for search. Also, when a Document is deleted, its sub-Collections are not deleted and become unreachable, which can become very costly over time.
Connections to Firestore usually rely on HTTP but can use WebSockets. Cross-Origin Resource Sharing requests are managed by Google when applicable.