perf/bfcache-no-unload

Why

With the back/forward cache, going back shows the page instantly with LCP, CLS and INP of a cached page. An unload listener makes Firefox skip the cache and Chrome is phasing the event out; unload also does not fire reliably on mobile, so the code it guards is lost anyway.

Fix

Move the work to pagehide (fires on every navigation away, cache or not) or to visibilitychange when document.visibilityState === 'hidden' (the last reliable moment on mobile). Send analytics with navigator.sendBeacon or fetch(…, { keepalive: true }). Check third-party scripts too: DevTools > Application > Back/forward cache lists what blocks it.

Examples

// bad
window.addEventListener('unload', sendStats)
// good
window.addEventListener('pagehide', sendStats)
document.addEventListener('visibilitychange', () => { if (document.visibilityState === 'hidden') saveDraft() })

Sources

• web.dev, Back/forward cache (never use the unload event)
• Chrome for Developers, Deprecating the unload event
• MDN, Window pagehide event

Read it in the terminal

npx github:dawidolko/frontend-skills explain perf/bfcache-no-unload