# Nextjs Patterns

> Next.js frontend conventions: App Router structure, a single lib/api.ts client with namespaced calls, trailing-slash endpoints, dayjs dates, and component/state patterns for frontend-centric and SSR modes. Apply when writing or reviewing Next.js/React UI code.

- Skill: `theyoungastronauts/nextjs-patterns` (Agent Skill)
- Install (CLI): `npx skillmds@latest add theyoungastronauts/nextjs-patterns`
- Raw SKILL.md: https://api.skillmd.com/api/skills/theyoungastronauts/nextjs-patterns/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Web & Frontend
- Author: theyoungastronauts (https://skillmd.com/u/theyoungastronauts)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/theyoungastronauts/nextjs-patterns

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# Skill: Next.js Patterns

## Purpose
Guide Claude Code when implementing Next.js features. Projects use one of two modes — check the project's CLAUDE.md or ask.

## Project Structure
- Use App Router (`src/app/` directory) with `@/*` path alias
- Components organized by feature (`components/goals/`, `components/settings/`), not by type
- Shared UI components in `components/ui/` with barrel `index.ts` exports
- Custom hooks in `lib/hooks/` with barrel `index.ts` exports
- All API types in a single `types/api.ts` — split only if it exceeds ~800 lines
- All API functions in a single `lib/api.ts` organized into namespaced objects

## Components
- PascalCase filenames matching the component name, default exports
- Props interface defined above the component, suffixed with `Props`
- Use `import type { ... }` for type-only imports
- Always handle loading, empty, and error states on every page

## API Client
- Single `lib/api.ts` with generic `apiFetch<T>` base function
- Namespaced exports per domain: `authApi`, `itemsApi`, etc.
- `ApiError` class with `status`, `message`, `data` fields
- Trailing slashes on all endpoints (Django REST Framework convention)
- UUIDs as primary identifiers in URLs

## Styling
- Semantic color tokens from your UI library — never hardcoded hex in components
- Responsive-first — mobile breakpoints before desktop

## Types
- `interface` for object shapes, `type` for unions/aliases
- String literal unions for status fields (not enums)
- Separate `CreateRequest` / `UpdateRequest` types (update fields optional)
- Dates from backend are `string` (ISO 8601) — parse with `dayjs`

## Naming
- Components: PascalCase files + default exports
- Hooks: camelCase with `use` prefix, named exports
- API namespaces: camelCase with `Api` suffix (`itemsApi`)
- Constants: `UPPER_SNAKE_CASE`
- Directories: kebab-case for routes, camelCase for lib

## Development Environment
- All commands run via `make` (Docker Compose under the hood) — never run `npm` directly on the host
- Use the matching bootstrap command (`/nextjs-bootstrap`, `/nextjs-mui-bootstrap`, or `/nextjs-shadcn-bootstrap`) when setting up a new project from scratch
- Hot reload works inside Docker via `WATCHPACK_POLLING=true`
- `node_modules` lives inside the container (anonymous volume) — do not install on host

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## Frontend-Centric Mode
SPA-like architecture, decoupled from backend. Most components are interactive.

- Most components use `'use client'` — client-first approach
- Data fetching: `useEffect` + `useState` (no React Query/SWR)
- State: React Context for global (auth/user), `useState` for local — no Redux/Zustand
- Auth: JWT via localStorage (`lib/auth.ts`), `UserContext` + `useUser()` hook, `useRequireAuth()` guard, `router.replace` for redirects — no Next.js middleware
  - Tradeoff: localStorage tokens are readable by any injected script, so an XSS bug leaks the refresh token (and thus long-lived access). Acceptable for a decoupled SPA with disciplined output-escaping/CSP. If you need to survive XSS, store the refresh token in an httpOnly, Secure, SameSite cookie the JS can't read (refresh via a backend route) and keep only the short-lived access token in memory.
- Errors: try/catch with `ApiError` instanceof check + `react-hot-toast`, always `finally` for loading state
- Use `/nextjs-bootstrap` with frontend-centric mode to scaffold

## SSR-Centric Mode
Server-rendered, leveraging Next.js built-in features.

- Default to Server Components; `'use client'` only for interactivity, hooks, browser APIs
- Data fetching: Server Components fetch directly; client components use React Query/SWR
- State: React Query for server state, Context or Zustand for complex UI state
- Auth: Next.js middleware or server-side session checks
- Errors: `error.tsx` boundaries at route level, `loading.tsx` / Suspense for loading states
- Testing: React Testing Library, MSW for API mocking, Playwright for E2E
- Use `/nextjs-bootstrap` with SSR-centric mode to scaffold