The Page Visibility specification lets developers detect when their application is in the foreground, and thus adapt their operations and resource consumption accordingly.
Technologies in progress
Whether packaged or not, users rely on a variety of metadata (name, icons) to identify the apps they want to use among their list of regularly used applications. The Web App Manifest specification lets developers group all these metadata into a single JSON file.
The Service Workers specification describes a method that enables applications to take advantage of persistent background processing, opening the door to running applications offline.
Not only does Service Workers enables Web applications to work seamlessly offline or in poor network conditions, it also creates a model for Web applications to operate when they have not been opened in a browser window, or even if the browser itself is not running. That ability opens the door for Web applications that run in the background and can react to remotely triggered events.
The Push API enables Web applications to subscribe to remote notifications that, upon reception, wake them up. Native applications have long enjoyed the benefits of greater user engagement that these notifications bring.
Through support for background operations, the Geolocation Sensor specification allows Web applications to be woken up when a device enters a specified geographical area, also known as geofencing.
The Web Packaging document describes use cases for a new package format for web sites and applications and outlines such a format.
The Badging API defines a more subtle notification mechanism than Web Notifications, allowing Web applications that have been installed on the device (e.g. through a manifest file) to set an application-wide badge, typically shown next to the application's icon on the home screen, to notify the user when the state of the application has changed and might require their attention (e.g. a new message has arrived).
Applications running on mobile devices can go through different application states, from running to being idle, paused, stopped, discarded, or terminated. Transitions between these states are triggered by the underlying operating system, and hidden from web applications. The Page Lifecycle proposal seeks to expose application state transitions to applications so that these applications can persist/restore state, enable/disable use of network, etc.
The Web Background Synchronization specification builds on top of Service Workers to enable Web applications to keep their user data up to date seamlessly, by running network operations in the background, adjusting to possibly unreliable connections that users often experience on mobile devices.
Background Fetch defines a similar service worker based download and upload mechanism in the background, but allows the background operation to continue, with user visibility, even if the user closes all windows and workers. The specification is specifically tailored to enable downloads/uploads of large assets (podcasts, movies, textures).
- Application caches
- The application cache mechanism was introduced in HTML5 to enable access to Web applications offline through the definition of a manifest of files that the browser is expected to keep in its cache. The feature is well deployed but raises security issues and is extremely limited in terms of how much developers can control what gets cached when. The feature was obsoleted in HTML 5.1, and dropped from HTML 5.2, in favor of the Service Workers specification, which defines a much more powerful approach.
- Task Scheduling
- The Task Scheduler API made it possible to trigger a task at a specified time via the service worker associated with a Web app. This specification was in scope of the now-closed System Applications Working Group and was shelved as a result.
- Geofencing API
- The Geofencing API made it possible to wake up a Web app when a device enters a specified geographical area. This work has been discontinued, partly out of struggles to find a good approach to permission needs that such an API triggers to protect users against privacy issues. Through support for background operations, the Geolocation Sensor specification now provides similar functionalities.
- Background execution control
- User agents will restrict the ability for Web applications to run operations in the background so that users remain in control of what an application can do at all times. The Web Budget API proposed a mechanism by which applications could determine the cost and budget at their disposal to run operations in the background, allowing them to decide whether to perform or postpone these operations. Various parameters could influence the cost of an operation, including whether the device is on battery power and the type of network the device is connected to. This proposal was dropped for lack of adoption and concerns over the design of such an API.