tailscale-custom/.agent/.shared/ui-ux-pro-max/data/react-performance.csv

1	No	Category	Issue	Keywords	Platform	Description	Do	Don't	Code Example Good	Code Example Bad	Severity
2	1	Async Waterfall	Defer Await	async await defer branch	React/Next.js	Move await into branches where actually used to avoid blocking unused code paths	Move await operations into branches where they're needed	Await at top of function blocking all branches	if (skip) return { skipped: true }; const data = await fetch()	const data = await fetch(); if (skip) return { skipped: true }	Critical
3	2	Async Waterfall	Promise.all Parallel	promise all parallel concurrent	React/Next.js	Execute independent async operations concurrently using Promise.all()	Use Promise.all() for independent operations	Sequential await for independent operations	const [user, posts] = await Promise.all([fetchUser(), fetchPosts()])	const user = await fetchUser(); const posts = await fetchPosts()	Critical
4	3	Async Waterfall	Dependency Parallelization	better-all dependency parallel	React/Next.js	Use better-all for operations with partial dependencies to maximize parallelism	Use better-all to start each task at earliest possible moment	Wait for unrelated data before starting dependent fetch	await all({ user() {}, config() {}, profile() { return fetch((await this.$.user).id) } })	const [user, config] = await Promise.all([...]); const profile = await fetchProfile(user.id)	Critical
5	4	Async Waterfall	API Route Optimization	api route waterfall promise	React/Next.js	In API routes start independent operations immediately even if not awaited yet	Start promises early and await late	Sequential awaits in API handlers	const sessionP = auth(); const configP = fetchConfig(); const session = await sessionP	const session = await auth(); const config = await fetchConfig()	Critical
6	5	Async Waterfall	Suspense Boundaries	suspense streaming boundary	React/Next.js	Use Suspense to show wrapper UI faster while data loads	Wrap async components in Suspense boundaries	Await data blocking entire page render	<Suspense fallback={<Skeleton />}><DataDisplay /></Suspense>	const data = await fetchData(); return <DataDisplay data={data} />	High
7	6	Bundle Size	Barrel Imports	barrel import direct path	React/Next.js	Import directly from source files instead of barrel files to avoid loading unused modules	Import directly from source path	Import from barrel/index files	import Check from 'lucide-react/dist/esm/icons/check'	import { Check } from 'lucide-react'	Critical
8	7	Bundle Size	Dynamic Imports	dynamic import lazy next	React/Next.js	Use next/dynamic to lazy-load large components not needed on initial render	Use dynamic() for heavy components	Import heavy components at top level	const Monaco = dynamic(() => import('./monaco'), { ssr: false })	import { MonacoEditor } from './monaco-editor'	Critical
9	8	Bundle Size	Defer Third Party	analytics defer third-party	React/Next.js	Load analytics and logging after hydration since they don't block interaction	Load non-critical scripts after hydration	Include analytics in main bundle	const Analytics = dynamic(() => import('@vercel/analytics'), { ssr: false })	import { Analytics } from '@vercel/analytics/react'	Medium
10	9	Bundle Size	Conditional Loading	conditional module lazy	React/Next.js	Load large data or modules only when a feature is activated	Dynamic import when feature enabled	Import large modules unconditionally	useEffect(() => { if (enabled) import('./heavy.js') }, [enabled])	import { heavyData } from './heavy.js'	High
11	10	Bundle Size	Preload Intent	preload hover focus intent	React/Next.js	Preload heavy bundles on hover/focus before they're needed	Preload on user intent signals	Load only on click	onMouseEnter={() => import('./editor')}	onClick={() => import('./editor')}	Medium
12	11	Server	React.cache Dedup	react cache deduplicate request	React/Next.js	Use React.cache() for server-side request deduplication within single request	Wrap data fetchers with cache()	Fetch same data multiple times in tree	export const getUser = cache(async () => await db.user.find())	export async function getUser() { return await db.user.find() }	Medium
13	12	Server	LRU Cache Cross-Request	lru cache cross request	React/Next.js	Use LRU cache for data shared across sequential requests	Use LRU for cross-request caching	Refetch same data on every request	const cache = new LRUCache({ max: 1000, ttl: 5*60*1000 })	Always fetch from database	High
14	13	Server	Minimize Serialization	serialization rsc boundary	React/Next.js	Only pass fields that client actually uses across RSC boundaries	Pass only needed fields to client components	Pass entire objects to client	<Profile name={user.name} />	<Profile user={user} /> // 50 fields serialized	High
15	14	Server	Parallel Fetching	parallel fetch component composition	React/Next.js	Restructure components to parallelize data fetching in RSC	Use component composition for parallel fetches	Sequential fetches in parent component	<Header /><Sidebar /> // both fetch in parallel	const header = await fetchHeader(); return <><div>{header}</div><Sidebar /></>	Critical
16	15	Server	After Non-blocking	after non-blocking logging	React/Next.js	Use Next.js after() to schedule work after response is sent	Use after() for logging/analytics	Block response for non-critical operations	after(async () => { await logAction() }); return Response.json(data)	await logAction(); return Response.json(data)	Medium
17	16	Client	SWR Deduplication	swr dedup cache revalidate	React/Next.js	Use SWR for automatic request deduplication and caching	Use useSWR for client data fetching	Manual fetch in useEffect	const { data } = useSWR('/api/users', fetcher)	useEffect(() => { fetch('/api/users').then(setUsers) }, [])	Medium-High
18	17	Client	Event Listener Dedup	event listener deduplicate global	React/Next.js	Share global event listeners across component instances	Use useSWRSubscription for shared listeners	Register listener per component instance	useSWRSubscription('global-keydown', () => { window.addEventListener... })	useEffect(() => { window.addEventListener('keydown', handler) }, [])	Low
19	18	Rerender	Defer State Reads	state read callback subscription	React/Next.js	Don't subscribe to state only used in callbacks	Read state on-demand in callbacks	Subscribe to state used only in handlers	const handleClick = () => { const params = new URLSearchParams(location.search) }	const params = useSearchParams(); const handleClick = () => { params.get('ref') }	Medium
20	19	Rerender	Memoized Components	memo extract expensive	React/Next.js	Extract expensive work into memoized components for early returns	Extract to memo() components	Compute expensive values before early return	const UserAvatar = memo(({ user }) => ...); if (loading) return <Skeleton />	const avatar = useMemo(() => compute(user)); if (loading) return <Skeleton />	Medium
21	20	Rerender	Narrow Dependencies	effect dependency primitive	React/Next.js	Specify primitive dependencies instead of objects in effects	Use primitive values in dependency arrays	Use object references as dependencies	useEffect(() => { console.log(user.id) }, [user.id])	useEffect(() => { console.log(user.id) }, [user])	Low
22	21	Rerender	Derived State	derived boolean subscription	React/Next.js	Subscribe to derived booleans instead of continuous values	Use derived boolean state	Subscribe to continuous values	const isMobile = useMediaQuery('(max-width: 767px)')	const width = useWindowWidth(); const isMobile = width < 768	Medium
23	22	Rerender	Functional setState	functional setstate callback	React/Next.js	Use functional setState updates for stable callbacks and no stale closures	Use functional form: setState(curr => ...)	Reference state directly in setState	setItems(curr => [...curr, newItem])	setItems([...items, newItem]) // items in deps	Medium
24	23	Rerender	Lazy State Init	usestate lazy initialization	React/Next.js	Pass function to useState for expensive initial values	Use function form for expensive init	Compute expensive value directly	useState(() => buildSearchIndex(items))	useState(buildSearchIndex(items)) // runs every render	Medium
25	24	Rerender	Transitions	starttransition non-urgent	React/Next.js	Mark frequent non-urgent state updates as transitions	Use startTransition for non-urgent updates	Block UI on every state change	startTransition(() => setScrollY(window.scrollY))	setScrollY(window.scrollY) // blocks on every scroll	Medium
26	25	Rendering	SVG Animation Wrapper	svg animation wrapper div	React/Next.js	Wrap SVG in div and animate wrapper for hardware acceleration	Animate div wrapper around SVG	Animate SVG element directly	<div class='animate-spin'><svg>...</svg></div>	<svg class='animate-spin'>...</svg>	Low
27	26	Rendering	Content Visibility	content-visibility auto	React/Next.js	Apply content-visibility: auto to defer off-screen rendering	Use content-visibility for long lists	Render all list items immediately	.item { content-visibility: auto; contain-intrinsic-size: 0 80px }	Render 1000 items without optimization	High
28	27	Rendering	Hoist Static JSX	hoist static jsx element	React/Next.js	Extract static JSX outside components to avoid re-creation	Hoist static elements to module scope	Create static elements inside components	const skeleton = <div class='animate-pulse' />; function C() { return skeleton }	function C() { return <div class='animate-pulse' /> }	Low
29	28	Rendering	Hydration No Flicker	hydration mismatch flicker	React/Next.js	Use inline script to set client-only data before hydration	Inject sync script for client-only values	Use useEffect causing flash	<script dangerouslySetInnerHTML={{ __html: 'el.className = localStorage.theme' }} />	useEffect(() => setTheme(localStorage.theme), []) // flickers	Medium
30	29	Rendering	Conditional Render	conditional render ternary	React/Next.js	Use ternary instead of && when condition can be 0 or NaN	Use explicit ternary for conditionals	Use && with potentially falsy numbers	{count > 0 ? <Badge>{count}</Badge> : null}	{count && <Badge>{count}</Badge>} // renders '0'	Low
31	30	Rendering	Activity Component	activity show hide preserve	React/Next.js	Use Activity component to preserve state/DOM for toggled components	Use Activity for expensive toggle components	Unmount/remount on visibility toggle	<Activity mode={isOpen ? 'visible' : 'hidden'}><Menu /></Activity>	{isOpen && <Menu />} // loses state	Medium
32	31	JS Perf	Batch DOM CSS	batch dom css reflow	React/Next.js	Group CSS changes via classes or cssText to minimize reflows	Use class toggle or cssText	Change styles one property at a time	element.classList.add('highlighted')	el.style.width='100px'; el.style.height='200px'	Medium
33	32	JS Perf	Index Map Lookup	map index lookup find	React/Next.js	Build Map for repeated lookups instead of multiple .find() calls	Build index Map for O(1) lookups	Use .find() in loops	const byId = new Map(users.map(u => [u.id, u])); byId.get(id)	users.find(u => u.id === order.userId) // O(n) each time	Low-Medium
34	33	JS Perf	Cache Property Access	cache property loop	React/Next.js	Cache object property lookups in hot paths	Cache values before loops	Access nested properties in loops	const val = obj.config.settings.value; for (...) process(val)	for (...) process(obj.config.settings.value)	Low-Medium
35	34	JS Perf	Cache Function Results	memoize cache function	React/Next.js	Use module-level Map to cache repeated function results	Use Map cache for repeated calls	Recompute same values repeatedly	const cache = new Map(); if (cache.has(x)) return cache.get(x)	slugify(name) // called 100 times same input	Medium
36	35	JS Perf	Cache Storage API	localstorage cache read	React/Next.js	Cache localStorage/sessionStorage reads in memory	Cache storage reads in Map	Read storage on every call	if (!cache.has(key)) cache.set(key, localStorage.getItem(key))	localStorage.getItem('theme') // every call	Low-Medium
37	36	JS Perf	Combine Iterations	combine filter map loop	React/Next.js	Combine multiple filter/map into single loop	Single loop for multiple categorizations	Chain multiple filter() calls	for (u of users) { if (u.isAdmin) admins.push(u); if (u.isTester) testers.push(u) }	users.filter(admin); users.filter(tester); users.filter(inactive)	Low-Medium
38	37	JS Perf	Length Check First	length check array compare	React/Next.js	Check array lengths before expensive comparisons	Early return if lengths differ	Always run expensive comparison	if (a.length !== b.length) return true; // then compare	a.sort().join() !== b.sort().join() // even when lengths differ	Medium-High
39	38	JS Perf	Early Return	early return exit function	React/Next.js	Return early when result is determined to skip processing	Return immediately on first error	Process all items then check errors	for (u of users) { if (!u.email) return { error: 'Email required' } }	let hasError; for (...) { if (!email) hasError=true }; if (hasError)...	Low-Medium
40	39	JS Perf	Hoist RegExp	regexp hoist module	React/Next.js	Don't create RegExp inside render - hoist or memoize	Hoist RegExp to module scope	Create RegExp every render	const EMAIL_RE = /^[^@]+@[^@]+$/; function validate() { EMAIL_RE.test(x) }	function C() { const re = new RegExp(pattern); re.test(x) }	Low-Medium
41	40	JS Perf	Loop Min Max	loop min max sort	React/Next.js	Use loop for min/max instead of sort - O(n) vs O(n log n)	Single pass loop for min/max	Sort array to find min/max	let max = arr[0]; for (x of arr) if (x > max) max = x	arr.sort((a,b) => b-a)[0] // O(n log n)	Low
42	41	JS Perf	Set Map Lookups	set map includes has	React/Next.js	Use Set/Map for O(1) lookups instead of array.includes()	Convert to Set for membership checks	Use .includes() for repeated checks	const allowed = new Set(['a','b']); allowed.has(id)	const allowed = ['a','b']; allowed.includes(id)	Low-Medium
43	42	JS Perf	toSorted Immutable	tosorted sort immutable	React/Next.js	Use toSorted() instead of sort() to avoid mutating arrays	Use toSorted() for immutability	Mutate arrays with sort()	users.toSorted((a,b) => a.name.localeCompare(b.name))	users.sort((a,b) => a.name.localeCompare(b.name)) // mutates	Medium-High
44	43	Advanced	Event Handler Refs	useeffectevent ref handler	React/Next.js	Store callbacks in refs for stable effect subscriptions	Use useEffectEvent for stable handlers	Re-subscribe on every callback change	const onEvent = useEffectEvent(handler); useEffect(() => { listen(onEvent) }, [])	useEffect(() => { listen(handler) }, [handler]) // re-subscribes	Low
45	44	Advanced	useLatest Hook	uselatest ref callback	React/Next.js	Access latest values in callbacks without adding to dependency arrays	Use useLatest for fresh values in stable callbacks	Add callback to effect dependencies	const cbRef = useLatest(cb); useEffect(() => { setTimeout(() => cbRef.current()) }, [])	useEffect(() => { setTimeout(() => cb()) }, [cb]) // re-runs	Low