demo · v133

Page lifecycle state machine

The energy-saver freeze sits inside the existing page-lifecycle state machine. Watch the live state for this tab move between active, passive, hidden, frozen, and terminated — and what events fire on each transition.

stateactive
statepassive
statehidden
statefrozen
stateterminated
document.visibilityState —
document.wasDiscarded —
pings since attach 0
persistent draft (not saved)

switch to another tab and stay away for several minutes to provoke freeze on Energy Saver.

the four hooks you actually need

document.addEventListener("freeze",   () => { localStorage.draft = current; });
document.addEventListener("resume",   () => { current = localStorage.draft; });
document.addEventListener("visibilitychange", () => { /* pause heavy work */ });
window.addEventListener("pagehide",   (e) => { if (e.persisted) parkInBfcache(); });

Pre-energy-saver, freeze on the desktop only fired when you closed the browser or when bfcache evicted. Now it fires reliably after ~5 min of background + CPU-busy, so every web app that holds in-memory state (WIP forms, draft uploads, undo buffers) should ship a freeze handler that persists state to localStorage or IndexedDB.

see also