Frontend - React

When to use this skill

• Feature work or fixes in React apps using TypeScript.
• Creating components, routing, forms, state management, or API integration.
• Testing, linting, performance tuning, or accessibility improvements.

Quick start

1. Install deps: npm ci (or project-standard package manager).
2. Env: copy .env.example -> .env; set VITE_ or REACT_APP_ vars per stack.
3. Dev: npm run dev (Vite) or npm start (CRA). Build: npm run build. Preview: npm run preview if Vite.
4. Quality: npm run lint; tests: npm test or npm run test:unit (Vitest/Jest).

Project structure basics

• src/main.tsx or src/index.tsx: app bootstrap; wraps providers (router, store, query client).
• Routing: react-router with lazy createBrowserRouter/Suspense for code splitting.
• State: prefer React Query for server state; lightweight local state with hooks; global state with context or Zustand/Recoil as needed.
• UI components: keep props typed; avoid prop drilling via context where appropriate.

Coding principles

• Keep components focused; lift/share state only when necessary; type everything.
• Treat loading/error/empty states as first-class; normalize API errors.
• Use error boundaries for critical sections; ensure suspense fallbacks exist for lazy routes.
• Enforce lint/type/test/build before merge (run scripts/dev-check.sh).

Patterns and snippets

• Ready-to-use component, fetch, routing, and form patterns live in references/snippets.md.
• Centralize HTTP client (fetch/axios) for auth/error handling; prefer React Query for server state.
• Use react-hook-form + schema validation for forms; show per-field errors and disable submit while pending.

Testing

• Component tests with Testing Library; assert on user-facing behavior, not internals.
• Mock network calls; verify loading/error/success states.

Accessibility and UI

• Prefer semantic HTML; ensure labels for inputs; manage focus on navigation and modals.
• Support keyboard interactions; ensure color contrast; provide skip links if relevant.

Bundled resources

• scripts/dev-check.sh: run before commit/PR to validate lint, type-check, tests, and build using the detected package manager.
• references/coding-standards.md: quick guardrails on component sizing, typing, error states, and pre-merge checks.
• references/best-practices.md: deeper guidance for structure, routing, state, API clients, styling, testing, performance, and a11y.
• references/snippets.md: component/data-fetch/form/routing patterns ready to copy.
• assets/pr-template.md: apply when opening PRs so reviewers get scope, testing proof, and UI evidence in a consistent format.

Delivery checklist

• Lint, tests, and type checks pass.
• No stray console logs; env vars documented; API errors mapped to user-friendly messages.
• Routes lazy-loaded where beneficial; suspense fallbacks present; loading and empty states handled.