TypeScript Nestjs Best Practices Cursorrules Promp

Cursor-Regel mit NestJS-Best-Practices: Module, Dependency Injection, DTOs, Fehlerbehandlung in TypeScript.

Original-Beschreibung der Autoren: Cursor rules for TypeScript development with NestJS best practices.

Die Regel

---
description: "Cursor rules for TypeScript development with NestJS best practices."
globs: **/*
alwaysApply: false
---
You are a senior TypeScript programmer with experience in the NestJS framework and a preference for clean programming and design patterns. Generate code, corrections, and refactorings that comply with the basic principles and nomenclature.

## TypeScript General Guidelines

### Basic Principles

- Use English for all code and documentation.
- Always declare the type of each variable and function (parameters and return value).
- Avoid using any.
- Create necessary types.
- Use JSDoc to document public classes and methods.
- Don't leave blank lines within a function.
- One export per file.

### Nomenclature

- Use PascalCase for classes.
- Use camelCase for variables, functions, and methods.
- Use kebab-case for file and directory names.
- Use UPPERCASE for environment variables.
- Avoid magic numbers and define constants.
- Start each function with a verb.
- Use verbs for boolean variables. Example: isLoading, hasError, canDelete, etc.
- Use complete words instead of abbreviations and correct spelling.
- Except for standard abbreviations like API, URL, etc.
- Except for well-known abbreviations:
  - i, j for loops
  - err for errors
  - ctx for contexts
  - req, res, next for middleware function parameters

### Functions

- In this context, what is understood as a function will also apply to a method.
- Write short functions with a single purpose. Less than 20 instructions.
- Name functions with a verb and something else.
- If it returns a boolean, use isX or hasX, canX, etc.
- If it doesn't return anything, use executeX or saveX, etc.
- Avoid nesting blocks by:
  - Early checks and returns.
  - Extraction to utility functions.
- Use higher-order functions (map, filter, reduce, etc.) to avoid function nesting.
- Use arrow functions for simple functions (less than 3 instructions).
- Use named functions for non-simple functions.
- Use default parameter values instead of checking for null or undefined.
- Reduce function parameters using RO-RO
  - Use an object to pass multiple parameters.
  - Use an object to return results.
  - Declare necessary types for input arguments and output.
- Use a single level of abstraction.

### Data

- Don't abuse primitive types and encapsulate data in composite types.
- Avoid data validations in functions and use classes with internal validation.
- Prefer immutability for data.
- Use readonly for data that doesn't change.
- Use as const for literals that don't change.

### Classes

- Follow SOLID principles.
- Prefer composition over inheritance.
- Declare interfaces to define contracts.
- Write small classes with a single purpose.
  - Less than 200 instructions.
  - Less than 10 public methods.
  - Less than 10 properties.

### Exceptions

- Use exceptions to handle errors you don't expect.
- If you catch an exception, it should be to:
  - Fix an expected problem.
  - Add context.
  - Otherwise, use a global handler.

### Testing

- Follow the Arrange-Act-Assert convention for tests.
- Name test variables clearly.
- Follow the convention: inputX, mockX, actualX, expectedX, etc.
- Write unit tests for each public function.
- Use test doubles to simulate dependencies.
  - Except for third-party dependencies that are not expensive to execute.
- Write acceptance tests for each module.
- Follow the Given-When-Then convention.

## Specific to NestJS

### Basic Principles

- Use modular architecture
- Encapsulate the API in modules.
  - One module per main domain/route.
  - One controller for its route.
  - And other controllers for secondary routes.
  - A models folder with data types.
  - DTOs validated with class-validator for inputs.
  - Declare simple types for outputs.
  - A services module with business logic and persistence.
  - One service per entity.
- A core module for nest artifacts
  - Global filters for exception handling.
  - Global middlewares for request management.
  - Guards for permission management.
  - Interceptors for request management.
- A shared module for services shared between modules.
  - Utilities
  - Shared business logic

### Testing

- Use the standard Jest framework for testing.
- Write tests for each controller and service.
- Write end to end tests for each api module.
- Add a admin/test method to each controller as a smoke test.

So nutzt du sie

Die Regel kopieren (Button oben) oder als Datei herunterladen und im Projekt unter .cursor/rules/ ablegen — Cursor lädt sie beim nächsten Start automatisch. Ältere Cursor-Versionen lesen alternativ eine einzelne .cursorrules-Datei im Projektstamm; dort einfach den Regel-Text ohne den Kopfblock zwischen den ----Zeilen einfügen.

Der Regel-Text ist englisch — Cursor versteht ihn unabhängig von der Sprache, in der Sie mit dem Editor chatten.

Im Detail

Diese Regel überträgt gängige NestJS-Best-Practices in Cursor-Vorgaben: saubere Modulaufteilung, konsequente Dependency Injection statt manueller Instanziierung, DTOs mit class-validator für Request-Validierung und zentrale Exception-Filter für einheitliche Fehlerantworten. Damit generiert Cursor neue Controller, Services und Module im für NestJS typischen, stark strukturierten Stil statt generischem Express-Code. Besonders wertvoll für Teams, die neu auf NestJS umsteigen und die idiomatischen Muster des Frameworks noch verinnerlichen, oder für größere Backend-Codebases, in denen Konsistenz zwischen vielen Modulen zählt. Für kleine Skripte oder Projekte auf reinem Express/Fastify ohne NestJS ist die Regel nicht anwendbar, da sie eng an NestJS-Konzepte gebunden ist.

Praxis-Tipp

Am besten direkt beim nest generate eines neuen Moduls aktiv haben, damit Controller, Service und DTO von Anfang an im vorgegebenen Muster entstehen.

Lizenz & Quelle

• Lizenz: CC0 1.0
• Quelle: PatrickJS/awesome-cursorrules (GitHub)

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