# Getting started with NestJS

If you have ever created server-side apps using NodeJS, you might have used express, fastify or other HTTP framework. Although, these are very easy to get started and perfect for small projects involving small team. But, if you want to create a project which will last longer and has many contributors, you need a good application architecture to align the team. You may create this by yourself or you can use existing framework like **Nest** to accomplish the goal.

## What is Nest
**[Nest(NestJS)](https://nestjs.com/)** is a framework for building efficient, scalable Node.js server-side applications. 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. So, let's get started:

## Prerequisites
1. [Node.js](https://nodejs.org/en/) (version >= 12, except version 13)
2. [npm](https://www.npmjs.com/), which is installed along with Node.js

## Install Nest CLI
To create nest applications, we need [Nest cli](https://docs.nestjs.com/cli/overview). Run the following command to install it
```
npm install --global @nestjs/cli
```

## Create a new project
Let's create a new project `nest-blogs` using nest cli. Run the below command to create the project
```
nest new --strict nest-blogs
```
When it asks to select a package manager to use, select any one you want to use. I selected `npm` and will be using that. It will take some time since it will install the required node modules as well. Here, the optional `--strict` flag enables the strict mode in TypeScript.

## Project Structure
Open the `nest-blogs` directory in any code editor or IDE. We have the following files in the project

![Project structure of a new project created using nest cli](https://cdn.hashnode.com/res/hashnode/image/upload/v1665903904225/39WTLWkfQ.png align="center")
Let's take a look at the purpose of each file in brief:
1. The `package.json` file has information about the project, a list of npm dependencies required for the project, and some useful scripts.
2. The ` tsconfig.json` and `tsconfig.build.json` files specify the root files and the compiler options required to compile the project.
3. The `nest-cli.json` file is used by the nest to keep the metadata needed to organize, build and deploy the project.
4. The `.prettierrc` file is a configuration file used by [Prettier](https://prettier.io/) tool to format the code.
5. The `.eslintrc.js` file is used by [ESLint](https://eslint.org/) to identify and report on patterns found in ECMAScript/Javascript code.
6. The `app.controller.ts` is a basic controller with a single route. Controllers are used to map the incoming request to specific functions and to return the response back to the client.
7. The `app.controller.spec.ts` is a unit test for the controller.
8. The `app.service.ts` is a basic service with a single method. Services are the places where we put the business logic of the application.
9. The `app.module.ts` is the root module of the application. Modules are used to divide the application into seperate parts depending on the responsibility.
10. The `main.ts` is the entry point of the application which uses the core function `NestFactory` to create a nest application instance.

## Running the application
While creating the application, if required node modules are not installed due to some reason or if you have used `--skip-install` flag, run the below command to install packages now from the `nest-blogs` directory
```
npm install
```
Run the below command to start the applicatin:
```
npm start
```
Open `http://localhost:3000/` url in the browser. You should see **Hello World!** on the page. Press `Ctrl ^ c` in the terminal to stop the app. While developing the app, we want the app to restart automatically as soon as we make any changes. To do that, run the below command in the terminal:
```
npm run start:dev
```
If we again go to the same link, we see the same text. Now, do the following:
1. Open 'app.service.ts` file in editor.
2. Change `getHello` method to return `Hello Universe` instead of `Hello World!`.
  ```
  import { Injectable } from '@nestjs/common';
  
  @Injectable()
  export class AppService {
    getHello(): string {
      return 'Hello Universe';
    }
  }
  ```
3. Save the file.
4. Go to the same link and reload the page.
5. We see **Hello Universe** on the page.

This way, we don't need to stop and start the server manually. It will restart as soon as it detects changes in any project-related file(s).

## Platform
Nest can work with any Node HTTP framework using adapters. Nest provides out-of-the-box adapters for two HTTP frameworks - [express](https://expressjs.com/) and [fastify](https://www.fastify.io/).
1. `platform-express` is the adapter for `express` and it is used by default in Nest projects. We don't have to do anything additional to use express.
2. `platform-fastify` is the adapter for `fastify`. To work with *fastify* instead of *express*, below steps are required - 
  1. Install the required package using
    ```
    npm install --save @nestjs/platform-fastify
    ```
  2. Modify `main.ts` to use `FastifyAdapter` to create the application
    ```
    import { NestFactory } from '@nestjs/core';
    import {
      FastifyAdapter,
      NestFastifyApplication,
    } from '@nestjs/platform-fastify';
    import { AppModule } from './app.module';
    
    async function bootstrap() {
      const app = await NestFactory.create<NestFastifyApplication>(
        AppModule,
        new FastifyAdapter(),
      );
      await app.listen(3000);
    }
    bootstrap();
    ```
  3. Restart the application and make sure it works.

## Summary
In this article, we have setup a basic Nest project. In the upcoming blogs, we will explore more. You can find the project on [github](https://github.com/himanshu-pareek/nest-blogs/tree/01_getting_started_with_nestjs). Please provide your feedback in the comments. We will meet in the next blog. Until then, happy learning.