Clean Architecture, SOLID, and Folder Structure Design - Textnotes

Clean Architecture, SOLID, and Folder Structure Design

Learn how to structure TypeScript projects using clean architecture, SOLID principles, and well-organized folder structures. This module explains best practices for building scalable, maintainable, and robust applications

1. Clean Architecture Principles

Clean architecture separates concerns to make projects modular, testable, and maintainable.

Key Layers

  1. Presentation Layer: Handles UI, API endpoints, and user interactions
  2. Domain Layer: Contains business logic and domain models
  3. Data Layer: Handles database access, API calls, and persistence

Benefits

  1. Independent layers that can evolve separately
  2. Easy to write unit tests
  3. Reduces coupling and improves maintainability

2. SOLID Principles

SOLID principles guide maintainable and scalable object-oriented design.

Single Responsibility Principle (SRP)

Each class or module should have one responsibility.

Open/Closed Principle (OCP)

Modules should be open for extension but closed for modification.

Liskov Substitution Principle (LSP)

Derived classes should be replaceable with their base classes without affecting correctness.

Interface Segregation Principle (ISP)

Interfaces should be small and specific; do not force modules to implement unused methods.

Dependency Inversion Principle (DIP)

Depend on abstractions, not concrete implementations.

Applying SOLID improves code readability, reduces bugs, and makes scaling easier.

3. Folder Structure Design

A well-designed folder structure enhances maintainability and collaboration.

Example Folder Structure


src/
├─ controllers/ # Handles HTTP requests and responses
├─ services/ # Business logic
├─ models/ # TypeScript interfaces and database models
├─ repositories/ # Database access layer
├─ routes/ # API routes
├─ middlewares/ # Express middleware
├─ utils/ # Helper functions
├─ config/ # Environment configuration
└─ tests/ # Unit and integration tests

Best Practices

  1. Group files by feature or layer
  2. Keep a clear separation of concerns
  3. Avoid deep nesting
  4. Name folders and files consistently

A clean folder structure reduces complexity and makes onboarding new developers easier.

Conclusion

Applying clean architecture principles, SOLID design patterns, and a structured folder layout ensures TypeScript projects are scalable, maintainable, and robust. Following these best practices improves collaboration, testing, and long-term project success