nestjs-clean-typescript

SKILL.md

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