Long and Non-Essential Tasks

Work that is correct but runs at the wrong moment. JavaScript runs to completion, so a task that holds the main thread holds every interaction queued behind it, and work the user is not waiting for should not compete with work they are.

Schedule non-essential work in an idle callback

Analytics, telemetry, prefetch and cache warming are not what the user is waiting for, so they should not compete with what is. requestIdleCallback runs them in the gaps between frames instead of on the startup path — analyticsActions.init() currently dispatches from a useEffect in Preloader.tsx, which is exactly the critical path this moves work off.

// bad - Preloader.tsx - analytics init competes with first paint and device discovery
useEffect(() => {
    dispatch(analyticsActions.init());
}, [dispatch]);

// good - the user sees the app first; the timeout guarantees it still runs
useEffect(() => {
    const id = requestIdleCallback(() => dispatch(analyticsActions.init()), { timeout: 2000 });

    return () => cancelIdleCallback(id);
}, [dispatch]);

Always pass timeout: without one a busy page can go seconds before the callback fires, and on a page that never idles it may not fire at all. requestIdleCallback is not Baseline — no Safari — so web needs a setTimeout fallback, and React Native has no such API, so this is a web and desktop rule only. It is also not a dumping ground: nothing the user is waiting on, and no DOM writes that have to land in a particular frame, because the callback runs with a budget it expects you to respect. There are no call sites in the repo yet, so the first one sets the pattern.

Related skills

• Asymptotic complexity — indexing, sorting and reducing over collections that grow.
• React hooks — memoization, dependency arrays, render loops.
• DOM and CSS — forced layout, observers, compositor-only animation.