Transition from Express to NestJS

In today’s dynamic development ecosystem, staying up-to-date with new frameworks and technologies is essential. NestJS, with its modular architecture, TypeScript integration, and built-in dependency injection, offers significant advantages over Express. Migrating to NestJS can unlock better scalability, maintainability, and performance for your backend systems.

This article provides a step-by-step guide to help you seamlessly transition your existing Express application to NestJS. By following this process, you’ll leverage the full potential of NestJS and future-proof your backend architecture.

Prerequisites

Before diving into the migration steps, make sure the following tools are installed:

• Node.js (version 8.9 or higher)
• NPM or Yarn as your package manager
• TypeScript compiler

Additionally, having some prior knowledge of Express, TypeScript, and Node.js will make the migration smoother.

Step-by-Step Migration from Express to NestJS

Step 1: Create a New NestJS Project

To begin, install the NestJS CLI globally:

npm install -g @nestjs/cli

Now, create a new NestJS project:

nest new <your-project-name>

Replace your-project-name with the desired name for your project. Select the preferred package manager. The CLI will scaffold the project with all necessary dependencies and structure, ready for development.

Step 2: Configure TypeScript

NestJS is built on TypeScript, so ensure that both your old Express application and the new NestJS project are configured for TypeScript compilation.

Install TypeScript and its required dependencies:

npm install --save typescript @types/node ts-node

Configure the tsconfig.json file as per your project requirements. This setup allows you to write TypeScript code across both Express and NestJS during the migration.

Step 3: Convert Express Routes into NestJS Controllers

NestJS organizes routes into controllers, which handle incoming requests and responses. Generate a controller using the CLI:

nest generate controller <controller name>

In the generated controller file (controller-name.controller.ts), replicate the routes from your Express application using decorators like @Get(), @Post(), @Put(), and @Delete():

Express Route Example:

app.get('/users', (req, res) => {
  res.send('User list');
});

NestJS Controller Example:

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

@Controller('users')
export class UserController {
  @Get()
  findAll() {
    return 'User list';
  }
}

For route parameters, query parameters, request bodies, or handling request and response objects, use the appropriate NestJS decorators such as @Param(), @Query(), @Body(), @Req(), and @Res().

Step 4: Implement Services and Modules

NestJS encourages modular design by separating business logic into services. Move your core logic from controllers into dedicated services to align with NestJS best practices.

Generate a service using the Nest CLI:

nest generate service <service name>

Service files are used to write business logic, database interactions etc.

Similarly, create modules to organize your application better:

nest generate module <module name>

NestJS modules encapsulate related functionality, making your application more maintainable. For more information on services and modules, refer to the official NestJS documentation.

Step 5: Test Your Application

After migrating your components — routes, controllers, and services — thoroughly test the application to ensure everything works as expected.

Now, start the application in the terminal or command prompt using the command below in the root directory path.

$ npm run start

Use unit testing and end-to-end testing for better code quality. NestJS has built-in support for testing, and its documentation offers great guidance on setting up tests.

Extra Operations

For more advanced features like translating Express middleware to NestJS middleware, implementing interceptors, adding authentication, authorization, guards, etc., you can refer to the official documentation.

Conclusion

Migrating from Express to NestJS improves your application’s modularity, scalability, and maintainability. This guide helps you streamline the migration process, allowing you to fully leverage the power of NestJS.

Make sure to test your application thoroughly post-migration and stay up-to-date with the latest practices and tools in NestJS to get the most out of it. With this transition, your backend is now more robust and ready to tackle the challenges of modern web development.

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