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The app storage family of elements gives you a new set of tools for managing data in your app. The initial set includes ready-made elements for integrating with Firebase and PouchDB.

The Firebase 3.0.0 SDK supports a new set of Firebase elements, built with app storage, called PolymerFire. These elements make critical Firebase SDK integrations such as app initialization, user authentication, and database access declarative, and easier than ever before.

The <app-indexeddb-mirror> element provides a read-only mirror of a database like Firebase. This ensures that users will have access to their personal data even when there is no network available.

Firebase is resilient to temporary losses of network connectivity—like when a user suddenly goes through a tunnel while using your Firebase app. Firebase continues to work and update the server as soon it reconnects to the network. But there are other offline cases that Firebase—and other popular storage layers—don’t handle very well, like when a user starts the app while offline.

The Polymer app-pouchdb component contains elements for PouchDB document access, database querying, synchronization across local and remote databases and even user authentication with a remote CouchDB instance. Since PouchDB can automatically synchronize data with a local IndexedDB database, it has never been easier to add offline-first data access to your progressive web app.