React.js

React 19 (released December 2024) introduced three meaningful additions: the Actions API for async mutations that replaces manual loading/error state; new hooks (useFormStatus, useActionState, useOptimistic) that integrate with Actions for cleaner async form handling; and improved custom element support. Separately, the React Compiler v1.0 shipped in October 2025 as a production-stable Babel plugin. For most production React 18 apps, upgrading to React 19 is low-risk given the backwards compatibility maintained across versions. The Compiler is the more impactful change — it eliminates the manual memoization boilerplate that creates noise in most React codebases.

Use Server Components (the default in Next.js App Router) for anything that: fetches data from a database or API, imports large server-side libraries, handles sensitive business logic, or has no user interaction. These components don't contribute to the client JS bundle. Add 'use client' only when you need browser APIs, React hooks (useState/useEffect), event handlers, or real-time state updates. The practical result for data-heavy apps: 40–80% smaller client JS bundles. The mental model shift: React components now run in two environments — thinking about which environment each component belongs to is the main new skill RSC requires.

For most teams building production applications, yes. Svelte and Solid have genuine technical advantages — smaller bundles, simpler reactivity, faster raw benchmarks. React Compiler substantially closes the performance gap. The practical question is whether React's 69.74% framework market share, 96M weekly downloads, and deep production validation match your constraints — they typically do. The exception: if bundle size is a hard constraint (embedded widgets, very low-end device targeting), Svelte's compile-time approach is worth taking seriously. If your team has deep Svelte expertise, that expertise is worth more than framework choice in most cases.

Server state: React Query (TanStack Query) v5 for data fetching, caching, and server synchronization — handles 70-80% of what applications call 'state management'. Client state: Zustand for global UI state not coming from a server. React built-in useState/useContext for component-local state. For new projects, avoid Redux unless you're inheriting a Redux codebase — Redux Toolkit is a significant improvement over vanilla Redux, but React Query + Zustand handles the same patterns with substantially less boilerplate. Jotai is worth considering for apps with complex atomic state dependencies.

Client-side-only React (Vite + React without SSR) has Google indexing limitations because content appears after JavaScript execution — not unindexable, but slower to index and potentially ranking below server-rendered equivalents for competitive queries. Next.js App Router with React Server Components eliminates this: the first response is server-rendered HTML, fully indexable immediately. For any application where organic search matters — e-commerce, content, SaaS with a public marketing site — Next.js + RSC is the standard approach and is what we use by default.

React Compiler is a build-time Babel/SWC plugin that analyzes React components statically and automatically adds memoization — the same optimization developers previously wrote manually with useMemo, useCallback, and React.memo. v1.0 shipped stable in October 2025. You should use it if: your React 19 components follow the rules of hooks (no mutations of external state, no unsafe patterns) and you want automatic performance optimization without the cognitive overhead of manual memoization. Run it in 'annotation mode' first to see which components it successfully compiles — most well-written React 18+ code is compatible without changes.

Marketing site or landing page: 1–3 weeks. SaaS MVP with authentication, core CRUD, and a basic dashboard: 6–10 weeks. Full-featured SaaS with real-time data, multiple user roles, and billing integration: 4–6 months. The constraint is never React itself — it's requirements clarity, API design decisions, and scope management. We scope by deliverables, not by framework hours, because deliverables are what actually determine timelines. An 8-week project with clear requirements ships predictably; one with weekly scope additions doesn't, in any framework.

Yes — and we strongly recommend incremental migration over full rewrites. For jQuery apps: identify the most complex interactive components first, build them as React islands using ReactDOM.createRoot embedded in the existing HTML, validate each island in production before expanding. For Angular: the architectural difference is large enough that section-by-section rewrites are more common, but we do it in phases — new features in React, existing Angular sections preserved until each area is migrated. Full rewrites that freeze feature development for 3–6 months are high-risk; incremental migrations let your product continue shipping throughout.

Project scope varies significantly — a React frontend connecting to an existing API costs differently from a full-stack Next.js app with a new database design. What we can say: India-based senior React engineers with real production experience cost significantly less than equivalent engineers at US or UK agencies while delivering the same code quality. Share your project requirements and we'll give you a transparent scope-based cost breakdown. We've delivered React projects from 4-week MVPs to multi-year platform engagements.

Greenfield projects: Next.js 15 App Router, TypeScript throughout, React Query v5 (server state), Zustand (complex client state), React Hook Form + Zod (forms and validation), Tailwind CSS, Radix UI or shadcn/ui (accessible component primitives), React Compiler (automatic memoization), Vitest + React Testing Library (unit/integration), Playwright (E2E), Lighthouse CI in the deployment pipeline. This isn't dogma — we adjust for existing codebases, team expertise, and project constraints. But it's the stack we'd choose again for a greenfield project starting today, informed by production experience across 163+ shipped applications.