NestJS 11 cheatsheet

NestJS 11: Validation, guards and interceptors

7 common NestJS 11 tasks.

Describe and validate a request body

Use class-validator decorators on a DTO class.

export class CreateCatDto {
  @IsString()
  @MinLength(2)
  name: string;

  @IsInt()
  @Min(0)
  age: number;
}

Enable validation globally

Validate and transform every request body. whitelist removes properties the DTO doesn't declare.

app.useGlobalPipes(new ValidationPipe({ whitelist: true, transform: true }));

Protect routes with a guard

A guard decides whether a request may proceed. Throw or return false to deny it.

@Injectable()
export class AuthGuard implements CanActivate {
  canActivate(context: ExecutionContext): boolean {
    const request = context.switchToHttp().getRequest();
    return Boolean(request.headers.authorization);
  }
}

@UseGuards(AuthGuard)
@Get('profile')
profile() {}

Run code around handlers

An interceptor can log, transform responses or time requests.

@Injectable()
export class TimingInterceptor implements NestInterceptor {
  intercept(context: ExecutionContext, next: CallHandler) {
    const start = Date.now();
    return next.handle().pipe(tap(() => console.log(`took ${Date.now() - start}ms`)));
  }
}

Customize error responses

A filter turns exceptions into the responses you want.

@Catch(HttpException)
export class HttpErrorFilter implements ExceptionFilter {
  catch(exception: HttpException, host: ArgumentsHost) {
    const response = host.switchToHttp().getResponse();
    response.status(exception.getStatus()).json({ message: exception.message });
  }
}

Enable CORS

Allow browser apps on other origins to call the API.

const app = await NestFactory.create(AppModule);
app.enableCors({ origin: 'https://app.example.com' });

Generate OpenAPI docs

Serve an OpenAPI document and Swagger UI. Install @nestjs/swagger first.

const config = new DocumentBuilder().setTitle('Cats API').setVersion('1.0').build();
SwaggerModule.setup('docs', app, SwaggerModule.createDocument(app, config));