Advanced Nest.js Features: Exploring Advanced Features of Nest.js with Example and Deep Understanding

Advanced Nest.js Features: Exploring Advanced Features of Nest.js with Example and Deep Understanding

Nest.js is a highly popular framework for building server-side applications with Node.js. It offers a wide range of features that make it easy to develop maintainable, scalable, and testable code. In this blog post, we will explore some of the advanced features of Nest.js, including:

• Dependency Injection
• Modules
• Guards
• Interceptors
• Custom Decorators

Dependency Injection

Dependency injection is a design pattern that allows you to pass dependencies to a class or function as parameters. In Nest.js, dependency injection is achieved through the use of decorators. By annotating a class with the @Injectable() decorator, you can make it injectable. To inject a dependency into a class, you can use the @Inject() decorator.

Example:

import { Injectable } from '@nestjs/common';
import { UserService } from './user.service';

@Injectable()
export class AuthService {
  constructor(@Inject(UserService) private userService: UserService) {}

  // ...
}

Modules

Modules are a way to organize your Nest.jsアプリケーション. Each module can contain a set of related classes, providers, and controllers. Modules can be nested within other modules, allowing you to create a hierarchical structure for your application.

Example:

import { Module } from '@nestjs/common';
import { UserService } from './user.service';
import { UserController } from './user.controller';

@Module({
  providers: [UserService],
  controllers: [UserController],
})
export class UserModule {}

Guards

Guards are used to protect specific routes or actions in your Nest.js application. By implementing a guard, you can define criteria that must be met in order for a request to be processed. Guards can be used to verify authentication, authorization, or any other custom conditions.

Example:

import { Injectable, CanActivate, ExecutionContext } from '@nestjs/common';

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

Interceptors

Interceptors are used to intercept and modify the flow of requests and responses in your Nest.js application. They can be used for a variety of purposes, such as logging, error handling, and data transformation.

Example:

import { Injectable, NestInterceptor, ExecutionContext, CallHandler } from '@nestjs/common';
import { Observable } from 'rxjs';
import { tap } from 'rxjs/operators';

@Injectable()
export class LoggingInterceptor implements NestInterceptor {
  intercept(context: ExecutionContext, next: CallHandler): Observable<any> {
    console.log('Before...');

    return next
      .handle()
      .pipe(tap(() => console.log('After...')));
  }
}

Custom Decorators

Custom decorators allow you to extend the functionality of Nest.js by creating your own decorators. You can use custom decorators to create reusable logic, validate data, and perform other tasks.

Example:

import { createParamDecorator, ExecutionContext } from '@nestjs/common';

export const GetUserId = createParamDecorator((data: unknown, ctx: ExecutionContext): number => {
  const request = ctx.switchToHttp().getRequest();
  return request.user.id;
});

Conclusion

Nest.js is a powerful framework that offers a wide range of advanced features to help you build maintainable, scalable, and testable applications. By leveraging these features, you can create applications that are efficient, secure, and easy to maintain.