1. ExpressJS

1. ExpressJS vs NodeJS

NodeJS: Node JS is an open-source and cross-platform runtime environment for executing JavaScript code outside of a browser. You need to remember that Node JS is not a framework and it’s not a programming language. Most of the people are confused and understand it’s a framework or a programming language. We often use Node.js for building back-end services like APIs like Web App or Mobile App. It’s used in production by large companies such as Paypal, Uber, Netflix, Walmart, and so on.

ExpressJS: Express is a small web framework that sits on top of Node JS’s web server functionality to simplify its APIs and add helpful new features. It makes it easier to organize your application’s functionality with middleware and routing. It adds helpful utilities to Node JS’s HTTP objects. It facilitates the rendering of dynamic HTTP objects.

• Node JS is a platform for building i/o applications that are server-side event-driven and made using JavaScript.
• Express JS is a framework based on Node JS which is used for building web applications using approaches and principles of Node JS event-driven architecture.

Feature	Express JS	Node JS
Usage	It is used to build web-apps using approaches and principles of Node JS	It is used to build server-side, input-output, event-driven apps.
Level of features	More features than Node JS.	Fewer features.
Building Block	It is built on Node JS	It is built on Google’s V8 engine.
Written in	JavaScript	C, C++, JavaScript
Framework/Platform	Framework based on Node JS	Run-time platform or environment designed for server-side execution of JavaScript.
Controllers	Controllers are provided.	Controllers are not provided.
Routing	Routing is provided.	Routing is not provided.
Middleware	Uses middleware for the arrangement of functions systematically server-side.	Doesn’t use such a provision.
Coding time	It requires less coding time.	It requires more coding time.

🏗 The MVC Concept

Express apps often follow the MVC (Model-View-Controller) pattern:

• Model – Data logic (e.g., database access)
• View – Presentation (HTML templates)
• Controller – Application logic (routes & middleware)

2. npm vs Node.js

Both Node.js and NPM have their own command-line interfaces. The Node.js CLI allows developers to execute JavaScript code on the server side, while the NPM CLI is used for package management tasks such as installing and updating packages.

The NPM CLI is built on top of the Node.js CLI and provides additional functionality for managing packages and dependencies.

3. Environment Setup

Create a folder and issue the following command inside the folder

npm init -yes

IMPORTANT

--yes (or -y ) flag on the npm init command will populate all options with the default values automatically.

Will create a package.json file inside the folder

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

"main": "index.js"

• The "main": "server.js" field is primarily for module usage when your package is used as a dependency in other projects, telling Node.js which file to load first when the package is required.
• It is not directly related to how you start your application with node server.js or npm start

3.1 Install ExpressJS

Play

Crash Course of ExpressJS

Play

Advance Course of ExpressJS

npm install express

To avoid restarting the server every time on changes to the project

npm install nodemon

Installation of packages will append dependency section to the package.json file

package.json

{
  ...
  "dependencies": {
    "express": "^4.19.2",
    "nodemon": "^3.1.0",
  }
}

Modify the package.json file and add two lines in "scripts"

package.json

"scripts": {
  "start": "node index.js",
  "devStart": "nodemon index.js"
}

3.2 Create index.js File

index.js is the main file which will be executed by node.

index.js

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

app.get('/' , function(req, res){
    res.send("Hello World")
});

// starts the server and tells it to listen for incoming connections on port 3000.
app.listen(3000, function(){
    console.log('Listening on port 3000')
});

• app.get('/', ...) sets up a GET request handler for the root path (/) of your website.
• function(req, res) {...} is the callback that runs when someone visits /.
  • req = the request object (info from the client)
  • res = the response object (used to send a reply)

3.3 Start node server

node index.js
or
npm run start
or
npm start # works only for predefined scripts in npm

SPECIAL SCRIPTS

• npm start is a predefined (special) script in npm.
• If you don’t define a start script, npm defaults to node server.js if that file exists.
• npm start, test, restart, and stop are special commands and don’t require npm run
• Any other custom script must use npm run <script-name>

WARNING

If you start the server as above, every time the code is changed, the server needs to be restarted

Start server with nodeman

nodemon index.js
or
npm run devStart

Restarting of the server is not required every time the code is changed.

3.4 🧰 Useful npm Packages

• morgan – Logging
• dotenv – Load environment variables
• cors – Enable cross-origin requests
• helmet – Secure headers
• body-parser – Parse incoming request bodies