Features in NestJS That Are Difficult or Tedious in Express:

Built-in Dependency Injection (DI):

• NestJS has a powerful DI system out of the box, enabling better code organization and testability.
• Express requires manual setup or third-party libraries for DI, which can become cumbersome in large-scale apps.

Modular Architecture:

• NestJS encourages splitting the application into modules (feature-based or domain-based) for scalability.
• Express typically results in a flat, unstructured folder hierarchy without enforcing modularity.

Decorators and Declarative Code:

• NestJS leverages TypeScript decorators to define routes (@Get, @Postetc), middlewares (@UseGuards, @UseInterceptors) and validation (@body, @param).
• In Express, you manually define routes and middleware with less abstraction.

Built-in WebSockets and Microservices Support:

• NestJS provides first-class support for WebSocket gateways (@WebSocketGateway) and microservices via transport layers like RabbitMQ, Kafka, Redis etc.
• Express needs additional libraries (e.g., socket.io) with more manual configuration for real-time features.

Out-of-the-box Testing Support:

• NestJS has tools like TestModuleBuilder for easy integration and unit testing of services, controllers, and modules.
• Testing in Express requires piecing together frameworks like Jest/Mocha with extra setup.

Integrated Validation and Transformation:

• NestJS uses the class-validator and class-transformer libraries with decorators for input validation and data transformation (@IsString, @IsInt, etc.).
• In Express, validation typically relies on middleware like express-validator.

GraphQL Support:

• NestJS has built-in support for GraphQL with decorators like @Resolver and @Query.
• Setting up GraphQL with Express requires external libraries like apollo-server and more boilerplate.

Interceptors and Guards:

• NestJS provides Interceptors (e.g., for logging or transforming responses) and Guards (e.g., for role-based access control).
• These features require custom middleware and less elegant implementations in Express.

Event-driven Architecture:

• With NestJS, you can implement event-driven architecture using its EventEmitter module or external libraries seamlessly.
• In Express, event-driven systems need custom patterns and more boilerplate.

Swagger Integration:

• NestJS makes API documentation simple with @nestjs/swagger by generating it from your decorators.
• Express requires separate tools like swagger-jsdoc with more manual effort.