frontend-architecture

Frontend Architecture (portable, module-based)

Portable skill — readable by Claude Code, OpenCode, Codex, Cursor, Windsurf, and others. This skill describes a structure and a set of rules, not a component library, a state library, or a visual style. It is deliberately global: the same module/page/state model maps onto Next.js (App Router), React + Vite (SPA), Remix, and Expo / React Native, and it works with any state-management and styling stack.

The goal: a codebase where any contributor can instantly answer three questions — "where does this code live?", "what is allowed to import what?", and "is this server state or UI state?" — without asking anyone. The structure makes the answers obvious.

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0. The five core ideas

1. Feature modules own their world. Each feature is a self-contained modules/{feature}/ folder with its own pages, components, hooks, state, types, and a single public barrel.
2. Pages/screens are directories, not files. A route is a folder that co-locates its component, its styles, and the components/hooks used only by it.
3. State is split by origin. Server data lives in a query/cache layer. UI/client state lives in a store. They never overlap — regardless of which libraries you pick.
4. Imports cross boundaries only through barrels. Reaching into another module's internals is forbidden; you import from @/modules/{feature} and nothing deeper.
5. Code is promoted, not pre-placed. It starts as local as possible and moves outward only when a second consumer appears.

Everything below is the mechanical application of these five ideas. None of it is tied to a specific library — pick your stack in Sections 4 and 6.

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1. Directory layout

The shape is identical across frameworks; only the routing layer on top differs (see Section 7).

src/
├── app/ or routes/ or navigation/   ← framework routing layer (thin — see §7)
├── modules/                         ← feature modules (the heart of the app)
│   └── {feature}/
│       ├── index.ts                 ← PUBLIC BARREL — the only cross-module entry point
│       ├── README.md                ← what this module owns, its routes, its data deps
│       ├── components/              ← components reused by 2+ pages IN THIS MODULE
│       ├── pages/                   ← page/screen directories (one per route)
│       │   └── {page}/
│       │       ├── {page}.tsx               ← the page/screen component
│       │       ├── {page}.styles.ts         ← ALL styling for this page
│       │       ├── index.ts                 ← re-exports the page component
│       │       ├── components/              ← components used ONLY by this page
│       │       ├── hooks/                   ← hooks used ONLY by this page
│       │       ├── constants/
│       │       └── README.md                ← route, params, permissions, data deps
│       ├── hooks/                   ← data hooks (query/mutation) + module hooks
│       ├── stores/                  ← UI/client state store(s) — never server data
│       ├── services/                ← data-access (API calls) for this feature
│       ├── utils/                   ← pure module utilities (co-located *.test.ts)
│       ├── constants/
│       └── types/                   ← module request/response + view-model types
└── shared/                          ← cross-module building blocks
    ├── components/                  ← components used by 2+ MODULES
    ├── hooks/                       ← cross-cutting hooks
    ├── api-client/                  ← one typed client; the only place that talks to the network
    ├── store/                       ← root store wiring (if your state lib needs one — see §4)
    ├── utils/                       ← formatters, cn()/clsx, helpers
    ├── constants/
    └── types/