Page 3 - React

If you wait for the server to respond before the UI moves, you are giving away perceived speed. useOptimistic solves this problem right at the core of React: the UI state jumps forward immediately, gets adopted on success, and rolls back cleanly on failure, without manual state management.

useCallback and useMemo are the most frequently misused hooks in React. They always cost something: memory, runtime for the comparison, cognitive complexity, and they only help in specific, measurable situations. Using them everywhere makes an application slower, not faster.

Rewriting an entire grown JavaScript React project to TypeScript sounds like weeks of standstill. Whoever introduces TypeScript gradually enables allowJs, migrates file by file, and eventually reaches strict mode without ever interrupting feature work.

"My app behaves strangely in development mode, but runs flawlessly in production" is a warning sign, not a reason to relax. React Strict Mode makes visible bugs that will eventually surface in production. Running things twice is not a bug, it is a precise diagnostic strategy.

A form error, a new toast message, or an updated cart count all stay invisible to screen reader users as long as React only updates the DOM visually. An ARIA Live Region closes this gap by actively announcing changes without moving keyboard focus or interrupting ongoing input.

Long lists that load more content on scroll are one of the most common UI requirements, but naive implementations regularly fail on duplicates, memory usage and inconsistent scroll position. TanStack Query's infinite query solves these problems with a clear page structure, cursor based navigation, and combines with virtualization to render even tens of thousands of items smoothly.

String concatenation for Tailwind classes is error-prone, hard to read and does not scale to a real design system. The combination of clsx, tailwind-merge and class-variance-authority (CVA) solves this elegantly: type-safe variants, conflict-safe class merging and a single cn utility for the entire codebase.

An uncaught error in a React component destroys the entire component tree and shows the user a blank screen. Error Boundaries are the mechanism that isolates JavaScript errors in rendering, shows fallback UIs and keeps the application stable, when implemented correctly, reliably and with monitoring integration.

Next.js caches on four layers simultaneously, and many developers do not know which cache is firing or why. Request Memoization, Data Cache, Full Route Cache and Router Cache interact with each other and produce confusing results if you do not know their rules.

Incremental Static Regeneration combines the speed of static pages with the freshness of server-rendered content by regenerating individual pages in the background, without triggering a full rebuild. Using revalidate, revalidatePath, and revalidateTag correctly avoids stale content without losing the cache benefits.