Taming Codebases: Feature-Sliced Design (FSD) in React 🏗️

The "Folder Soup" Problem When starting a React or Next.js project, teams usually group files by technical layers: putting all UI elements in a components/ folder, and all hooks in a hooks/ folder. Organizing by technical type works early on, but as applications grow: Business logic becomes scattered across unrelated folders. When you need to update the "User Authentication" feature, you end up hunting through half a dozen directories to find the relevant pieces. At Smart Tech Devs, we architect our frontend systems for long-term maintainability. Feature-Sliced Design introduces a structured way to organize code based on business domains and responsibilities, not implementation details. Architecting by Domain In Feature-Sliced Design (FSD), the codebase is divided into vertical slices based on actual user value. The architecture relies on clear boundaries. Step 1: The Entry Points In FSD, Routes act as entry points into your application. Their only job is to declare the URL path and map it to a top-level Page component. They do not hold complex logic. Step 2: Composing the UI Once a route is hit, it renders a Page. Pages orchestrate UI and assemble widgets. Features handle user interactions and workflows. This prevents generic UI buttons from knowing too much about your specific API payloads. // ✅ THE ENTERPRISE PATTERN: Feature-Sliced Directory Structure src/ app/ # Routing layer (Next.js App Router) (auth)/login/page.tsx # Very thin route entry point pages/ # Page composition Login/ ui/LoginPage.tsx # Assembles the layout and widgets features/ # Business logic and user interactions Auth/ ui/LoginForm.tsx # The actual form interaction logic model/authStore.ts # State management specific to auth entities/ # Core business models User/ api/fetchUser.ts # Data fetching specific to the user entity types.ts shared/ # Highly reusable, domain-agnostic UI ui/Button.tsx lib/apiClient.ts The Engineering ROI By adopting Feature-Sliced Design, onboarding new developers becomes drastically faster. If a developer needs to fix a bug in the Shopping Cart, they navigate directly to the features/Cart/ slice, confident that the components, state, and API logic they need are tightly co-located, without fear of accidentally breaking the core User profile.