How to Build and use standalone applications with Nestjs

Building NestJS Standalone Applications Without an HTTP Network Listener

Introduction

NestJS is a popular Node.js framework that primarily focuses on building web applications using HTTP network listeners. However, there are scenarios where you might want to create a standalone application without relying on HTTP requests. In this blog post, we'll explore how to achieve this using NestJS's flexibility and modularity.

Understanding the Standalone Context

A standalone NestJS application can be used in various contexts, such as:

• Microservices: As individual components within a microservices architecture.
• CLI tools: To create command-line interfaces.
• Background jobs: For executing tasks asynchronously.
• Custom integrations: To integrate with other systems or platforms.

Key Considerations

When building a standalone NestJS application without an HTTP network listener, keep the following in mind:

• Module Bootstrapping: Manually bootstrap the NestJS application module to initialize the IoC container and configure dependencies.
• Dependency Injection: Utilize NestJS's dependency injection system to manage dependencies within your application.
• Custom Entry Points: Define custom entry points for your application to handle different use cases.
• Testing: Ensure thorough testing to verify the functionality of your standalone application.

Example: Creating a Standalone NestJS CLI Tool

import { NestFactory } from '@nestjs/core';
import { AppModule } from './app.module';

async function bootstrap() {
  const app = await NestFactory.createApplicationContext(AppModule);

  // Access and use the application context
  const myService = app.get('MyService');
  myService.runCommand();
}

bootstrap();

Explanation:

1. Create an application context: Use NestFactory.createApplicationContext() to create a NestJS application context without an HTTP network listener.
2. Access services: Use app.get() to retrieve services defined in your application module.
3. Execute your logic: Call the desired methods on the services to perform the intended actions.

Additional Considerations

• Configuration: Consider using environment variables or configuration files to manage settings in your standalone application.
• Logging: Implement logging to track the application's behavior and debug issues.
• Error handling: Implement proper error handling mechanisms to gracefully handle exceptions.
• Testing: Write unit and integration tests to ensure the correctness of your standalone application.

Conclusion

While NestJS is primarily designed for building web applications, it offers the flexibility to create standalone applications for various use cases. By understanding the key concepts and following the guidelines outlined in this blog post, you can effectively build and deploy standalone NestJS applications that meet your specific requirements.