NestJS Cheatsheet

🛠️

Controllers

Core

Handle incoming requests and return responses. Controllers are the main entry point for handling HTTP requests.

@Controller('users')
export class UsersController {

  @Get()
  async findAll() {
    return this.usersService.findAll();
  }
}

💡 Tip

Controllers must be decorated with @Controller() and can use route decorators like @Get(), @Post()

⚙️

Services

Core

Handle business logic and data operations. Services are injectable classes that provide specific functionality.

@Injectable()
export class UsersService {
  findAll(): Promise {}
}

⚠️ Note

Services must be decorated with @Injectable() to be injectable into other classes

📦

Modules

Core

Organize related components and dependencies. Modules group related functionality and manage dependencies.

@Module({
  controllers: [UsersController],
  providers: [UsersService]
})

💡 Tip

Modules are the basic building blocks of NestJS applications and help organize code into logical units

🏷️

Decorators

Core

Add metadata and behavior to classes and methods. Decorators are used to modify or enhance classes and methods.

@Controller()
@Get()
@Post()
@Injectable()
@Serialize(GetUserDto)

⚠️ Note

Decorators are a key feature of TypeScript that NestJS heavily relies on for its functionality

📝

Middleware

HTTP

Process requests before they reach route handlers. Similar to Express middleware, but with NestJS features.

app.use(loggerMiddleware);

💡 Tip

Middleware can be used to log requests, authenticate users, or modify request/response objects

🔄

Interceptors

HTTP

Process requests and responses. Interceptors can modify incoming requests or outgoing responses.

@UseInterceptors(LoggingInterceptor)
@UseInterceptors(SerializeInterceptor)

⚠️ Note

Interceptors are more powerful than middleware as they have access to both request and response objects

🔄

Pipes

Validation

Transform and validate input data. Pipes ensure that incoming data conforms to expected formats.

app.useGlobalPipes(new ValidationPipe());

💡 Tip

Pipes are great for data validation and transformation before it reaches your business logic

🔒

Guards

Security

Control access to routes and methods. Guards implement the authorization logic in your application.

@UseGuards(AuthGuard)
@UseGuards(RolesGuard)

⚠️ Note

Guards are used to protect routes and methods based on user roles or permissions

❌

Exception Filters

Error Handling

Handle exceptions globally. Exception filters catch and process errors that occur during request processing.

@Catch(HttpException)
handleException(exception: HttpException) {}

💡 Tip

Exception filters help maintain consistent error handling across your application

⚡

Events

Async

Handle events and notifications. Events allow components to communicate asynchronously.

@EventEmitter()
emit('user.created', user)

⚠️ Note

Events are great for implementing publish-subscribe patterns in your application