Knowledge documents in Frontend.
Which of the three layers — assertNever, satisfies Record, pattern matching libraries — to reach for and when, and why a catch-all default branch hides what you missed
Patterns where the type promises something the implementation never guarantees: the totality Record implies, type predicates that check nothing, ReturnType on wrappers that run later, and excess property checks mistaken for sanitizers
The order to follow: don't store what you can derive, don't copy a union the library already owns, and turn only what's left into a client-state union — plus why actions don't belong inside state
Why the same code passes in one repo and fails in another, and the procedure for pinning down your effective tsconfig and lockfile-resolved compiler version once, before you build any type contract
How to keep a list of allowed values in one place and compute the type from it instead of writing the list twice, plus the trap where widening silently removes that protection without a single error
Working around the fact that a const declaration can't take type parameters — creating the context inside a generic function and letting the components capture it by closure, plus the trap where calling it during render silently remounts everything
The rules that decide whether Dog[] and (x: Dog) => void inherit the Dog-is-an-Animal relationship, and in which direction — plus why method shorthand syntax leaves a hole even with strictFunctionTypes on
How injecting real pixel dimensions into markdown body images at build time eliminates both layout shift and fixed-ratio cropping
Instead of shipping polyfills to every browser, actually detect whether a feature is missing and load them only on the browsers that lack it — making the cost on modern browsers nearly zero
When several interactions on one screen stop working at once, it is usually not separate bugs but a single root cause: the client JS never ran, so hydration failed wholesale
Supporting old browsers is two different jobs — transpiling new syntax into old syntax, and polyfilling missing APIs with code. A transpiler only rewrites syntax; it does not create runtime functions
Lowering staleTime for instant reflection makes traffic explode. Keep staleTime as a freshness SLA and force a refetch at just that moment with invalidateQueries after a write — why and how
Do not hit protected APIs before session loading finishes; query enabled pattern that checks authResolved together with login state
UI knows only track/identify/reset; a thin layer fans events out to multiple analytics sinks such as GTM and PostHog
Rules and a single-source pattern: JSON-LD, FAQPage, and other structured data must contain only facts that appear in visible on-page text
The monorepo publish mechanism that links internal packages with workspace:* and rewrites it to real versions at publish time
A pattern that gathers neighbors within N hops via BFS over frontmatter related and wikilink indexes, then visualizes with force-graph
With localePrefix always, internal navigation must use next-intl Link so the active locale is preserved
A pattern that distinguishes same-slug documents with .{locale}.md filenames and aligns loader, DB, search, and SEO ids as type:slug:locale
A pattern that unifies bootstrap, React, and N-frame reassert into one corrective scroll so they do not compete in infinite-scroll window virtualizers
Web design trends derived by capturing and analyzing the landing pages of 10 hot 2026 startups (Cursor·Lovable·Granola etc.) with Playwright, measured for real
A zero-JS narrative pattern that syncs a product story to scroll using scroll-timeline, a sticky stage, and pure CSS keyframes — no GSAP
A navigation pattern that push/pops a documentId stack inside a single modal shell to connect gallery → peek → related
A pattern for navigating child documents in a block-document graph via page blocks, a push/peek navigator, and breadcrumbs
A pattern that splits the rich-text editor and read-only viewer entries to strip the PM/dnd bundle from peek/embed paths
A stale-while-populate pattern that warms a blur placeholder via peek + after() in SSR without adding TTFB
A pattern for building resize · webp conversion · CDN+LRU caching via a Route Handler in environments where built-in image optimization is disabled
A CQRS projection pattern that reduces nested-UI re-renders from O(depth) to O(1) via a normalized read-model over an immutable tree and per-id useSyncExternalStore subscriptions
A pattern for handling delete·mark·insert on a native selection spanning multiple blocks in a hybrid block editor, via stateless derivation and host patches
Why putting frequently-changing large state in a wide Context value defeats memo, and the narrow-Provider split pattern
Why using a fixed name and chunks:all on a catch-all vendor neutralizes dynamic import and hands every entry a giant shared vendor, and how to fix it
A client sync pattern that rolls back and re-applies a pending queue via local optimistic apply and inverse patches to converge with remote changes
How to keep editor-scoped styles by rendering inline when a Radix Popover Portal escapes the CSS scope ancestor
An editor architecture where the host owns document semantics and the rich-text engine is a guest briefly mounted on only the focused block
How Streaming SSR — which flushes HTML in chunks — affects FCP · LCP · SI · CLS, and the criteria for placing the LCP chunk
A history model that records edits as do/inverse pairs and shuttles state between two stacks — undo and redo
useSyncExternalStore compares snapshots with Object.is, so if the content changed but the value is equal it will miss the re-render forever
A pattern that prevents fetching images for off-screen slides in a horizontal carousel, eager-loading only the LCP candidate
A pattern for injecting schema.org JSON-LD into the server page.tsx in the Next.js App Router, with XSS sanitization
A pattern for filling a cache like React Query on the server to reduce the client auth→API waterfall, plus query key consistency
A technique that renders only rows near the viewport to the DOM in a long list, keeping memory·layout cost constant
How to separate priority, scope, and mode with @layer·@scope·light-dark() and custom properties to make token theming consistent
The causes of divergence between server-rendered HTML and the client's first render, and strategies for safely applying client-only state
An async UI pattern that guards against out-of-order responses using debounce, AbortController, and a latest-request id
The principle of deterministically generating sitemap · RSS · OG · JSON-LD at build time from a single frontmatter source
How LCP is measured and how to improve it
Browser resource prioritization and using fetchpriority