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Building Standalone Applications with NestJS

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Building Standalone Applications with NestJS

NestJS is a progressive Node.js framework built on top of TypeScript, inspired by Angular. It provides a robust and scalable structure for building efficient and maintainable server-side applications. While NestJS is commonly known for its capabilities in building REST APIs, its modularity and extensibility make it ideal for crafting standalone applications that can handle a wide range of tasks, from command-line tools to desktop applications.

In this comprehensive guide, we will explore the concepts, techniques, and tools that enable you to build standalone applications with NestJS. We will cover topics such as:

Understanding NestJS fundamentals
Developing standalone application logic
Integrating with external libraries and APIs
Handling user input and interaction
Building user interfaces with frameworks like Electron
Deploying and distributing standalone applications

Why Choose NestJS for Standalone Applications?

NestJS offers several advantages when building standalone applications:

Modular Architecture: NestJS promotes a clean, organized structure based on modules, making your codebase more manageable as it grows.
TypeScript Support: TypeScript provides type safety and improves code readability, leading to fewer errors and easier maintenance.
Dependency Injection: NestJS's dependency injection system simplifies managing dependencies, promoting reusability and reducing coupling.
Extensive Ecosystem: NestJS benefits from a rich ecosystem of modules and packages, offering a wide range of functionalities.
Testability: NestJS emphasizes testing through its design principles, making it easier to write unit tests and integration tests.

Building a Standalone Application with NestJS: A Practical Example

Let's build a simple standalone application that converts text to uppercase. This example will showcase how to create a NestJS module, handle user input, and integrate with an external library.

Creating a NestJS Project

Start by creating a new NestJS project using the Nest CLI:

nest new uppercase-app

Defining the Module

Navigate to the generated project directory and create a new module named uppercase by running:

nest generate module uppercase

This will create a new uppercase.module.ts file. In this file, define the module's structure and import the necessary dependencies:

import { Module } from '@nestjs/common';
import { UppercaseService } from './uppercase.service';
import { UppercaseController } from './uppercase.controller';

@Module({
  imports: [],
  controllers: [UppercaseController],
  providers: [UppercaseService],
})
export class UppercaseModule {}

Creating the Service

Create a new file named uppercase.service.ts within the uppercase directory. This service will handle the core logic of converting text to uppercase:

import { Injectable } from '@nestjs/common';

@Injectable()
export class UppercaseService {
  toUppercase(text: string): string {
    return text.toUpperCase();
  }
}

Creating the Controller

Create a new file named uppercase.controller.ts within the uppercase directory. This controller will handle user input and call the service to perform the conversion:

import { Controller, Get, Param } from '@nestjs/common';
import { UppercaseService } from './uppercase.service';

@Controller('uppercase')
export class UppercaseController {
  constructor(private readonly uppercaseService: UppercaseService) {}

  @Get(':text')
  uppercaseText(@Param('text') text: string) {
    return this.uppercaseService.toUppercase(text);
  }
}

Integrating with the Application

Now, import the UppercaseModule into your app.module.ts file to make it accessible within the application:

import { Module } from '@nestjs/common';
import { AppController } from './app.controller';
import { AppService } from './app.service';
import { UppercaseModule } from './uppercase/uppercase.module';

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

Running the Application

Start the application using:

npm run start

You can now access the uppercase endpoint at http://localhost:3000/uppercase/[your_text] in your browser to convert any text to uppercase.

Standalone Application Functionality

The code above demonstrates the basic structure of a NestJS application. To create a standalone application, you can extend this approach by adding:

Command-line Interface (CLI): Use a CLI framework like commander or yargs to provide a command-line interface for user interaction.
User Interface (UI): Integrate a UI framework like Electron to build a desktop application with a graphical interface.
File System Interactions: Use Node.js modules like fs to read and write files from your application.
Database Integration: Connect to a database like MongoDB or PostgreSQL to store and retrieve data.

Building a Desktop Application with Electron and NestJS

Electron is a framework that allows you to build cross-platform desktop applications using web technologies (HTML, CSS, JavaScript). You can leverage NestJS to create the backend logic for your Electron application, providing a robust and structured foundation.

Setting up Electron

Create a new directory for your Electron application and initialize a Node.js project using npm or yarn:

mkdir my-electron-app
cd my-electron-app
npm init -y

Installing Dependencies

Install the necessary Electron dependencies:

npm install electron

Creating the Main Process

Create a file named main.js in the root directory. This file is the entry point for your Electron application:

const { app, BrowserWindow } = require('electron');

function createWindow() {
  const win = new BrowserWindow({
    width: 800,
    height: 600,
    webPreferences: {
      nodeIntegration: true,
      contextIsolation: false, // Set to false for development
    },
  });

  win.loadFile('index.html'); // Load the HTML file
}

app.whenReady().then(createWindow);

Creating the Renderer Process (HTML/JS)

Create a file named index.html in the root directory. This file will be the HTML structure of your desktop application:

  <!DOCTYPE html>
  <html>
   <head>
    <title>
     My Electron App
    </title>
   </head>
   <body>
    <h1>
     Welcome to My Electron App
    </h1>
   </body>
  </html>

Integrating NestJS

You can either:

Embed NestJS: Run your NestJS server within the Electron application's main process. This allows for direct communication between the frontend and backend.
Separate Server: Run the NestJS application as a separate process and communicate with it via a network connection (e.g., HTTP). This offers better separation and scalability.

For this example, we'll use the embedded NestJS approach. Create a new directory named src and create a new NestJS project within it:

cd my-electron-app
mkdir src
cd src
nest new my-electron-app-backend

Now, you need to modify the main.js file to launch the NestJS server and load the Electron window:

const { app, BrowserWindow } = require('electron');
const path = require('path');
const { fork } = require('child_process');

function createWindow() {
  const win = new BrowserWindow({
    width: 800,
    height: 600,
    webPreferences: {
      nodeIntegration: true,
      contextIsolation: false,
    },
  });

  // Start the NestJS server
  const server = fork(path.join(__dirname, 'my-electron-app-backend', 'dist', 'my-electron-app-backend'), [], {
    stdio: 'inherit',
  });

  win.loadFile('index.html'); // Load the HTML file

  // Close the server when the Electron window closes
  win.on('closed', () =&gt; {
    server.kill();
  });
}

app.whenReady().then(createWindow);

Adding Functionality (Example: Text Conversion)

In your NestJS application (src/my-electron-app-backend), create a controller similar to the previous example to handle text conversion:

import { Controller, Get, Param } from '@nestjs/common';

@Controller('uppercase')
export class UppercaseController {
  @Get(':text')
  uppercaseText(@Param('text') text: string) {
    return text.toUpperCase();
  }
}

In your index.html, add a button and an input field to interact with the NestJS backend:

  <!DOCTYPE html>
  <html>
   <head>
    <title>
     My Electron App
    </title>
   </head>
   <body>
    <h1>
     Welcome to My Electron App
    </h1>
    <input id="input-text" type="text"/>
    <button id="convert-button">
     Convert to Uppercase
    </button>
    <p id="result">
    </p>
    <script>
     const inputText = document.getElementById('input-text');
      const convertButton = document.getElementById('convert-button');
      const result = document.getElementById('result');

      convertButton.addEventListener('click', () => {
        const text = inputText.value;
        fetch(`http://localhost:3000/uppercase/${text}`)
          .then(response => response.text())
          .then(uppercaseText => {
            result.textContent = uppercaseText;
          })
          .catch(error => {
            console.error('Error:', error);
          });
      });
    </script>
   </body>
  </html>

Running the Application

You can run the Electron application by running:

npm start

This will launch your desktop application, which will host the NestJS backend. You can now enter text in the input field and click the button to convert it to uppercase.

Conclusion

NestJS provides a robust and scalable framework for building standalone applications. By leveraging its modular structure, dependency injection, and TypeScript support, you can develop efficient and maintainable applications. You can create command-line tools, desktop applications, or other types of standalone software that leverage the power of NestJS.

Here are some key takeaways:

NestJS's architecture and features make it well-suited for standalone applications.
You can integrate NestJS with Electron to create cross-platform desktop applications.
By leveraging NestJS's ecosystem of modules, you can extend your applications with various functionalities.
Testing is crucial for standalone applications, and NestJS provides a foundation for comprehensive testing.

Remember to explore the NestJS documentation, examples, and community resources to learn more about building standalone applications. With NestJS, you have the power to create diverse and powerful applications that cater to a wide range of use cases.

Build standalone applications with Nestjs

Building Standalone Applications with NestJS

Why Choose NestJS for Standalone Applications?

Building a Standalone Application with NestJS: A Practical Example

Creating a NestJS Project

Defining the Module

Creating the Service

Creating the Controller

Integrating with the Application

Running the Application

Standalone Application Functionality

Building a Desktop Application with Electron and NestJS

Installing Dependencies

Creating the Main Process

Creating the Renderer Process (HTML/JS)

Integrating NestJS

Adding Functionality (Example: Text Conversion)

Running the Application

Conclusion