Add frozen or active lifecycleState to ServiceWorker Client

Category: Service Worker
Type: New or changed feature
Status: In developer trial (Behind a flag) (Chrome 77)
Intent stage: Evaluate readiness to ship

Summary

Exposes the client's PageLifecycle state on the ServiceWorker Client API.

Motivation

Service workers do not know the state of a client. If a client is frozen it will not immediately handle a postMessage() being sent to it. In some situations the service worker may not wish to spam the client with messages because that may cause the client to be discarded. In other situations the service worker may wish to focus the window client causing the client to become unfrozen.

Standards & signals

Specification: https://wicg.github.io/page-lifecycle/#service-worker-client-lifecycle-state
Firefox: No signal
Safari: No signal — Skepticism around whole Page Lifecycle API in general.
Web developers: No signals
Tracking bug: https://crbug.com/1002185

Docs: https://github.com/w3c/ServiceWorker/pull/1442

Explainers: https://github.com/dtapuska/iframe-freeze/blob/master/SW.md

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