Best NestJS Practices and Advanced Techniques
Tags: nestjs, backenddevelopment, backend, typescript
Published: 2023-08-23 19:11:10

NestJS has quickly gained popularity as a powerful framework for building scalable and maintainable Node.js applications. Its modular architecture, dependency injection system, and support for TypeScript make it an excellent choice for developing complex backend systems. In this blog post, we will explore some of the best practices and advanced techniques for working with NestJS to ensure that your projects are well-structured, performant, and easy to maintain.

**Table of Contents**

- Setting Up a NestJS Project
- Modular Architecture with Modules and Services
- Dependency Injection and Providers
- Controllers and Routing
- Data Validation and DTOs
- Error Handling and Logging
- Authentication and Authorization
- Testing with Jest
- Performance Optimization
- Deployment and Continuous Integration




 **Setting Up a NestJS Project**
To start a new NestJS project, you can use the Nest CLI:

Start by installing the NestJS CLI globally on your local machine and also  creating a new Project

```
$ npm install -g @nestjs/cli
$ nest new project-name
```
This will create a basic project structure with a default app module.


 **Modular Architecture with Modules and Services**
NestJS encourages a modular architecture to keep your codebase organized. Modules encapsulate related components, and services handle business logic. Here's an example of creating a module and service:

```
// users.module.ts
import { Module } from '@nestjs/common';
import { UsersController } from './users.controller';
import { UsersService } from './users.service';

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

// users.service.ts
import { Injectable } from '@nestjs/common';

@Injectable()
export class UsersService {
  private users = [];

  create(user) {
    this.users.push(user);
  }

  findAll() {
    return this.users;
  }
}
```

**Dependency Injection and Providers**
NestJS uses dependency injection to manage component dependencies. Providers are the building blocks of NestJS applications. They can be injected into other components like controllers and services.

```
// users.controller.ts
import { Controller, Post, Body } from '@nestjs/common';
import { UsersService } from './users.service';

@Controller('users')
export class UsersController {
  constructor(private readonly usersService: UsersService) {}

  @Post()
  create(@Body() user) {
    this.usersService.create(user);
  }
}
```

**Controllers and Routing**
Controllers define routes and request handling. They receive incoming requests, process them, and return responses.

```
// users.controller.ts
import { Controller, Get } from '@nestjs/common';
import { UsersService } from './users.service';

@Controller('users')
export class UsersController {
  constructor(private readonly usersService: UsersService) {}

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

```

** Data Validation and DTOs**
Using Data Transfer Objects (DTOs) helps validate incoming data and ensure type safety.

```
// create-user.dto.ts
export class CreateUserDto {
  readonly name: string;
  readonly age: number;
  readonly email: string;
}
```

```
// users.controller.ts
import { Controller, Post, Body } from '@nestjs/common';
import { UsersService } from './users.service';
import { CreateUserDto } from './create-user.dto';

@Controller('users')
export class UsersController {
  // ...

  @Post()
  create(@Body() createUserDto: CreateUserDto) {
    this.usersService.create(createUserDto);
  }
}

```

**Error Handling and Logging**
Implement global exception filters for consistent error handling and use logging for better debugging.

```
// http-exception.filter.ts
import { ExceptionFilter, Catch, ArgumentsHost, HttpException } from '@nestjs/common';

@Catch(HttpException)
export class HttpExceptionFilter implements ExceptionFilter {
  catch(exception: HttpException, host: ArgumentsHost) {
    // Handle exception and log details
  }
}

```

**Authentication and Authorization**
Implement authentication and authorization using guards and strategies to ensure only authorized access to the controller.

```
// auth.guard.ts
import { Injectable, CanActivate, ExecutionContext } from '@nestjs/common';

@Injectable()
export class AuthGuard implements CanActivate {
  canActivate(context: ExecutionContext) {
    // Implement authentication logic
    return true;
  }
}

```

**Testing with Jest**
NestJS supports testing with Jest. Write unit tests for services, controllers, and more.

```
// users.service.spec.ts
import { Test, TestingModule } from '@nestjs/testing';
import { UsersService } from './users.service';

describe('UsersService', () => {
  let service: UsersService;

  beforeEach(async () => {
    const module: TestingModule = await Test.createTestingModule({
      providers: [UsersService],
    }).compile();

    service = module.get<UsersService>(UsersService);
  });

  it('should be defined', () => {
    expect(service).toBeDefined();
  });
});
```

**Performance Optimization**
Performance optimization is crucial to ensuring that your NestJS application runs smoothly and efficiently. By following these techniques, you can enhance the speed, responsiveness, and scalability of your application.

Implement caching mechanisms to store frequently accessed data in memory, reducing the need to fetch it from the database repeatedly. The cache-manager package can be integrated seamlessly with NestJS to manage caching.

```
$ npm install cache-manager @nestjs/cache
```

```
import { CacheModule, Module } from '@nestjs/common';
import { AppController } from './app.controller';
import { AppService } from './app.service';

@Module({
  imports: [CacheModule.register()],
  controllers: [AppController],
  providers: [AppService],
})
export class AppModule {}

```

```
import { CacheInterceptor, CacheTTL, Controller, Get, UseInterceptors } from '@nestjs/common';
import { AppService } from './app.service';

@Controller()
export class AppController {
  constructor(private readonly appService: AppService) {}

  @Get('data')
  @UseInterceptors(CacheInterceptor)
  @CacheTTL(10) // Cache for 10 seconds
  getData() {
    return this.appService.getData();
  }
}

```

**Deployment and Continuous Integration**

Deploying your NestJS application and setting up a robust continuous integration (CI) pipeline are essential steps in the software development lifecycle. These processes ensure that your application is deployed reliably, tested thoroughly, and can scale seamlessly. Here's how to effectively deploy and manage your NestJS application.

Example Dockerfile:

```
FROM node:14

WORKDIR /app

COPY package*.json ./

RUN npm install

COPY . .

EXPOSE 3000

CMD ["npm", "run", "start:prod"]

```

For multi-container applications, use Docker Compose to define and manage your application's services and dependencies.

```
version: '3'
services:
  app:
    build:
      context: .
      dockerfile: Dockerfile
    ports:
      - '3000:3000'

```

Setting up CI ensures that your application is automatically built, tested, and deployed whenever changes are pushed to your version control repository. Tools like Jenkins, Travis CI, CircleCI, and GitLab CI/CD can help streamline this process.

Example .gitlab-ci.yml configuration:

```
stages:
  - build
  - test
  - deploy

build:
  stage: build
  script:
    - npm install
    - npm run build

test:
  stage: test
  script:
    - npm run test

deploy:
  stage: deploy
  script:
    - npm install -g @nestjs/cli
    - nest build
    - docker build -t my-nest-app .
    - docker login -u $DOCKER_USERNAME -p $DOCKER_PASSWORD
    - docker push my-nest-app

```



By following these best practices and advanced techniques, you can create robust and maintainable applications using NestJS. Its modular architecture, dependency injection system, and support for TypeScript enable you to build scalable and efficient backend systems with ease.

Remember that each project has its unique requirements, so adapt these techniques accordingly. Stay up-to-date with the NestJS documentation and the rapidly evolving Node.js ecosystem to make the most of this powerful framework. Happy coding!

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