A new guide outlines a layered architecture pattern for Next.js projects, emphasizing maintainability and testability. It details four core layers: Presentation (UI/API), Application (orchestration), Domain (business logic), and Infrastructure (data access). The guide includes a Mermaid diagram and code examples to visualize dependencies.

The core principle is separation of concerns, where each layer has a single responsibility. Crucially, the dependency rule states that higher layers must not depend on lower ones; dependencies flow inward. This prevents tangled code and eases future changes, a common pain point in growing React and Next.js applications.

The walkthrough provides a complete code example using TypeScript and Prisma. It shows how a ProductService in the Application layer calls a ProductRepository in Infrastructure, while the Presentation layer (a Next.js API route) only knows about the service interface. This structure isolates business rules from data access and UI concerns.

For testing, the guide recommends unit tests for Domain and Application layers with mocks, integration tests for Infrastructure, and end-to-end tests for Presentation. Avoiding pitfalls like circular dependencies or leaking infrastructure types is key. Adopting this scaffold can help teams manage complexity and accelerate delivery in Next.js codebases.