# NestJS

[NestJS](https://nestjs.com/) (Nest) is a [Node.js](https://nodejs.org/en/) framework for building server-side applications. It has full [Typescript](https://www.typescriptlang.org/) support and uses [Express](https://expressjs.com/) under the hoods, but can be configured to use [Fastify](https://www.fastify.io/) as well. Nest provides an out-of-the-box application architecture that allows developers and teams to create highly testable, scalable, loosely coupled, and easily maintainable applications. The architecture is heavily inspired by [Angular](https://angular.io/).

Talking about Angular, Nest has also a [CLI](https://docs.nestjs.com/cli/overview) that is very much useful and if used properly can help to follow standard conventions in the project. In this article, we will look at how to build a simple **GET REST API** using Nest.

First of all, we need to install CLI assuming we have Node.js & [NPM](https://www.npmjs.com/) already installed.

```bash
npm i -g @nestjs/cli
```

Then create a new project

```bash
nest new rest-api
```

Once you enter the above command, you will be asked to choose the package manager for this project. We will use NPM, but you can choose [Yarn](https://yarnpkg.com/) or other available options.

Once you are done with the above steps, open the folder with your project name (**rest-api** in this case) in any IDE or editor of your choice. We will use [VSCode](https://code.visualstudio.com/) here, but feel free to choose, what you are comfortable with. You will see a similar structure as below, based on your version of Nest.

![](https://cdn.hashnode.com/res/hashnode/image/upload/v1671975448395/6356209d-04fb-410a-87e7-2ac5b2749314.png align="center")

Expand the source folder and you will see 1 **main.ts** file and other app module files with the names **app.controller.ts**, **app.module.ts**, **app.service.ts,** and **app.controller.spec.ts**. Let's discuss the concepts related to the files that are created.

<table><tbody><tr><td colspan="1" rowspan="1"><p><code>app.controller.ts</code></p></td><td colspan="1" rowspan="1"><p>A basic controller with a single route.</p></td></tr><tr><td colspan="1" rowspan="1"><p><code>app.controller.spec.ts</code></p></td><td colspan="1" rowspan="1"><p>The unit tests for the controller.</p></td></tr><tr><td colspan="1" rowspan="1"><p><code>app.module.ts</code></p></td><td colspan="1" rowspan="1"><p>The root module of the application.</p></td></tr><tr><td colspan="1" rowspan="1"><p><code>app.service.ts</code></p></td><td colspan="1" rowspan="1"><p>A basic service with a single method.</p></td></tr><tr><td colspan="1" rowspan="1"><p><code>main.ts</code></p></td><td colspan="1" rowspan="1"><p>The entry file of the application which uses the core function <code>NestFactory</code> to create a Nest application instance.</p></td></tr></tbody></table>

### Module

It is a way to organize applications and put related functionality together. Each application must have at least 1 root module. [Read more](https://docs.nestjs.com/modules)

### Controller

Controller is meant for handling the request and sending the response back to the client. [Read more](https://docs.nestjs.com/controllers)

### Service

It holds the business logic for the application, like data storage, retrieval, and use by controllers. [Read more](https://docs.nestjs.com/providers#services)

For the purpose of this article let's create a simple **GET /developers** endpoint.

First, let's create a **developers** module and add a **controller** and **service** file. But, wait why not try Nest CLI? 😊

```bash
nest generate resource developers # select no for CRUD entry points
```

The above command will add a folder with files like below

![](https://cdn.hashnode.com/res/hashnode/image/upload/v1671981247952/757f66ec-6a65-401d-864d-582161918c3c.png align="center")

Open the controller file and modify it to look like the following code snippet.

```javascript
import { Controller, Get } from '@nestjs/common';
import { DevelopersService } from './developers.service';

@Controller('developers')
export class DevelopersController {

  // private readonly developersService: DevelopersService is Injecting 
  // the service here via DI pattern. 
  constructor(private readonly developersService: DevelopersService) {}

  @Get() // Here Get is basically HTTP GET
  findAll() {
    return this.developersService.findAll();
  }
}
```

Open the service file and modify it to look like following

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

@Injectable()
export class DevelopersService {
  findAll() {
    return [
      { name: 'Abdur Rehman', role: 'Full Stack Developer' },
      { name: 'Danish Alam', role: 'Full Stack Developer' },
    ];
  }
}
```

Now it's time to start the app. Use command below

```bash
npm run start:dev # run in root of project
```

Open [http://localhost:3000/developers](http://localhost:3000/developers) in any browser and you should see the response.✌  
You can find the source code [here](https://github.com/mann-codes2014/NestJS-Getting-Started-by-Building-a-REST-API/tree/rest-api-part-1).  

## References

[https://docs.nestjs.com/](https://docs.nestjs.com/)