TypeScript Nestjs Best Practices Cursorrules Promp

Cursor-Regel mit NestJS-Best-Practices für Module, Dependency Injection, DTOs und Fehlerbehandlung.

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

Eine Cursor-Regel für Backend-Projekte mit NestJS. Sie kodiert übliche Best Practices des Frameworks: klare Modulaufteilung, konsequente Nutzung von Dependency Injection statt manueller Instanziierung, DTOs mit Validierung für Ein- und Ausgabedaten sowie strukturierte Fehlerbehandlung über NestJS-eigene Exception-Filter. Besonders wertvoll für Entwickler, die neu in NestJS sind oder in einem Team arbeiten, das einheitlichen Code will, statt dass jeder Services und Controller unterschiedlich aufbaut. Im Vergleich zu freihändigem Prompting verhindert sie, dass die KI Express-typische statt NestJS-typische Muster vorschlägt.

Praxis-Tipp

Nützlich bei neuen Ressourcen, etwa mit „Erstelle ein Users-Modul mit Controller, Service, DTO-Validierung und passendem Exception-Filter“.

Lizenz & Quelle

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

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