SOLID Principles

A TODO application demonstrating SOLID principles with Clean Architecture (backend) and Feature-Sliced Design (frontend).

SOLID in Practice

The codebase applies SOLID principles as architectural decisions rather than isolated code patterns:

• Single Responsibility - Each layer and class has exactly one reason to change
• Open/Closed - The system extends through new modules, not by modifying existing ones
• Liskov Substitution - Parent abstractions never depend on their implementations
• Interface Segregation - Small, focused interfaces over broad ones
• Dependency Inversion - Business logic depends on abstractions, never on infrastructure

Architecture

Backend - Clean Architecture

Dependencies only point inward. Each module (todo, user) is self-contained:

modules/
  example/
    domain/          → Entities, Value Objects, Repository interfaces
    application/     → Use Cases, DTOs, Mappers
    presentation/    → Controllers, Routes
    infrastructure/  → PostgresTodoRepository

Frontend - Feature-Sliced Design

Dependencies only point downward:

app → pages → widgets → features → entities → shared

Tech Stack

Backend: Node.js, TypeScript, Express, PostgreSQL Frontend: React, TypeScript, Zustand, Vite Infrastructure: Docker, Docker Compose

Deployment

Dev

docker-compose up --build

Frontend served on port 5173, backend on 3001.

Prod

docker-compose -f docker-compose.prod.yml up -d

Frontend and API served on port 81 through nginx.