Getting started with Node.js

What is Node.js? and Why use it?

Node.js is a JS runtime environment which allows the infrastructure to build and run an application. It’s a light, scalable, and cross-platform way to execute code. It uses an event-driven I/O model which makes it extremely efficient and makes scalable network application possible.

There are many reasons why Node.js become popular below are just a few to name.

• Easy and fast to build real-time apps
• Many programmers are already familar with javascript
• It increases the efficiency of the development process as it fills the gap between frontend and backend developers
• It has hug ecosystem and tons of library to choose from.
• The single-threaded, event-driven architecture of Node.js allows it to handle multiple simultaneous connections efficiently. This allows it to handle hundreds of thousands or even a million concurrent connections
• Great for microservice

Installation

There are many different ways to get Node.js installed, but in this article I'm going to use nvm a node version manager to manage multiple node versions.

To install nvm enter the following command

$ curl -o- https://raw.githubusercontent.com/nvm-sh/nvm/v0.34.0/install.sh | bash

then to install specific version of node run the following command

$ nvm install 8.11.3
$ nvm use 8.11.3 # switch version

check if node is correctly installed

$ node -v
$ npm -v

NPM is the default node package manager and it comes pre-installed with the node runtime, but I prefer to use another package manager tool and it's called Yarn. To install it enter

$ curl -o- -L https://yarnpkg.com/install.sh | bash

The Basic

To start with the basic let's initialize a project by run the following command

$ mkdir demo
$ cd $_
$ yarn init # Or just `yarn` for existing project
$ # or using npm
$ npm init

this will create two files yarn.lock if you create project with yarn, and package.json. Every time you add new dependency these two files will be updated.

To add dependency run

$ yarn add {package-name} # or npm install {package-name} --save
$ yarn install # or npm install to fetch all dependencies listed in package.json

Type in node to open interactive console and play around.

$ node
> 10 + 20
30
> function hello() {
... console.log('hello')
... }
undefined
> hello()
hello
undefined

We can run node script by type node script.js. This will load the content of script.js file and evaluate it.

When the application grow large we can separate our code into separate file and import them. Node.js support a concept call module and anything that was assign to module.exports get exposed to the outside world and ready to be used. For example

// hello.js
module.exports = function() {
    console.log('hello');
}

to use this module we need to import it using require keyword and assign it to a variable like below

$ node
> const hello = require('./hello');
undefined
> hello()
hello
undefined

require accept a string which can be a relative path to a script file or a package name from node_modules directory which we will see in latter section when we start exploring third-party packages.

Node.js Project

Lets start by creating a RESTful service that serve JSON over HTTP for a Todo list. Open up your favorite text editor and enter the following code snippet.

// app.js
const express = require('express');

const app = express();
let todos = [];

app.use(express.json());

app.get('/todos', (req, res) => {
    res.status(200).json({
        data: todos,
    });
});

app.post('/todos', (req, res) => {
    const { body } = req;
    
    if (!body.name) {
        res.status(400).json({
            error: {
                name: 'is required',
            },
        });
    } else {
        todos.push(body.name);
        res.status(201).json({
            data: body.name,
        });
    }
});

app.delete('/todos/:name', (req, res) => {
    const { name } = req.params;
    const index = todos.find(todo => todo === name);
    
    if (index !== -1) {
        todos.splice(index, 1);
        res.status(204).json('success');
    } else {
        res.status(404).json({
            error: `can't find '${name}' in todo list.`,
        });
    }
});

const port = process.env.PORT || 8000;
app.listen(port, () => {
    console.log(`start listening on: http://localhost:${port}`);
});

We begin by importing a package name express, a popular Node.js web application framework. Then we create a server application instance. To add support for parsing a JSON payload we add a middleware function to our application instance with app.use. Then we add three routes to our web server by calling app.get, app.post and app.delete which in turn expose GET, POST and DELETE to /todos endpoint. The app.listen will start our web server on provided port number.

Before we could start our web application there is one more step we need to do. That is initialize a project and to pull in third-party package (express). Type in the following

$ yarn init
$ yarn add express

then we can start our application like this

$ node app.js

Go on and start making request to http://localhost:8000/todos to see the result.

A final step to make development easy is to add live code reloading by using a package name nodemon.

$ yarn nodemon --dev

the --dev flag tells yarn to add this package as a development only dependency. Now open package.json and add the following.

"scripts": {
    "start": "./node_modules/nodemon/nodemon.js app.js"
}

now we can start the server and watch for file changes with

$ yarn start