Node-and-Packages.md

Node and Packages

Node is a JavaScript runtime that allows building of server-side and client-side applications.

1. What is a package?

Node is shipped with a package manager, called npm, Node package manager, similar to Cocoapod or Swift Package manager allows for the installation of third party dependencies.

A package in Node can be used to add the following:

• Libraries
• Tools
• Shared Components
• Your app

2. npmjs.com

An online egistry to search for node packages.

3. Initialize npm in an application and create a package.json file

The package.json file is created when the following command is ran in terminal:

npm init

The package.json file contains the following:

• Metadata - your project's name, version, descrption, author, repository, license, etc
• Dependencies - the list of packages used by your project
• Scripts - commands to automate development tasks e.g npm start will run the application server

Example of a package.json file

{
  "name": "demo-web-server",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "keywords": [],
  "author": "Alex Paul",
  "license": "ISC"
}

To bypass initialization questions

npm init -y

4. Installing a package

Download and add package and dependencies to be included in production.

npm install <package-name>

Download and add package to dev dependencies that will only be used for development and not shipped with the app.

npm install --save-dev <package-name>

A few Node package installations and use cases

5. readline Package

1. Install readline package

The readline package allows for reading in user input from the command line.

npm install readline

2. require the package in your JavaScript file

const readline = require("readline");

3. Using the installed package

const r1 = readline.createInterface({
    input: process.stdin, 
    output: process.stdout
}); 

r1.question('Please enter your name?', (name) => {
    console.log(`Hello, ${answer}, welcome to Node development.`); 

    r1.close(); // need to close the readline connection to return to the application's regular execution
}); 

6.prettier Package

Prettier is used to format JavaScript code.

Install prettier

npm install --save-dev prettier

Edit the package.json scripts property to allow for quick running of format

"scripts": {
  "format": "prettier --write *.js"
}

Usage

npm run format

7. nodemon Package

Nodemon is used to automatically watch for changed files and re-run the node server.

Install nodemon

npm install -g nodemon // using the -g flag enables the package to be available globally throughout applications

Usage, now instead of using node <script name> to run a script we use:

nodemon <script name>

To restart a running application

rs

8. express Package

express is a Node package that allows us to create web servers to host APIs that allow for http request, reponses and supports HTTP methods e.g GET and POST.

Install express

npm install express

An example of web server JavaScript code that will listen on a specific port and render "Hello, world" if the API address is visited.

Save the following code in a file called index.js

const express = require('express'); 
const app = express(); 
const port = 3000; 

app.get('/', (request, response) => {
    response.send(`Hello World!`); 
}); 

app.listen(port, () => {
    console.log(`Example app listening at http://localhost:${port}`); 
}); 

To run the express web server

node index.js

Edit the package.json to include a run script

"scripts": {
  "start": "node index.js"
}

Using the run script

npm start

9. dotenv Package

dotenv allows for environment variables configuration, such as managing API keys and credentials.

Install dotenv

npm install dotenv

Edit the web server JavaScript file

require('dotenv').config(); 

const express = require('express'); 
const app = express(); 
const port = process.env.PORT; 

console.log(port); // 5000

Create a .env file

PORT=5000

Re-run the web server and all should still work as before, only this time the the port number is not exposed in the JavaScript code.

Don't forget to add your env file to the .gitignore

Read more about the dotenv Package