NestJS Clean TypeScript

Guidelines by Alberto Basalo for developing clean NestJS APIs using TypeScript. These rules emphasize strong typing, clean code principles, and architectural best practices.

TypeScript General Principles

• Always declare the type of each variable and function (parameters and return value)
• Avoid using any; create necessary types instead
• Use JSDoc for public classes and methods
• One export per file

Naming Conventions

• PascalCase for classes
• camelCase for variables and functions
• kebab-case for files and directories
• UPPERCASE for environment variables
• Boolean variables use prefixes: isX, hasX, canX

Function Design

• Write short functions with a single purpose. Less than 20 instructions
• Use early returns to avoid nesting
• Apply RO-RO pattern: pass objects for multiple parameters, return objects for results

Data and Classes

• Prefer immutability for data with readonly and as const
• Follow SOLID principles
• Classes should have:
  • Less than 200 instructions
  • Fewer than 10 public methods
  • Fewer than 10 properties

NestJS Specific Guidelines

• Use modular architecture with one module per domain/route
• Use MikroORM entities for persistence
• One service per entity
• DTOs validated with class-validator
• Global filters, middlewares, guards, and interceptors in core module

Testing

• Use Jest framework
• Follow Arrange-Act-Assert convention
• Write unit tests for each public function
• Include end-to-end tests per API module