Lesson 1: Key Concepts of NodeJS and Express for Backend Web Development

Introduction to Node.js:

• What is Node.js? An open-source, cross-platform JavaScript runtime environment that executes JavaScript code outside a browser.

• Why Node.js for Backend?

  • Non-blocking, event-driven architecture for efficient performance.

  • Single language (JavaScript) for both frontend and backend.

  • Large ecosystem via npm (Node Package Manager).

Core Concepts in Node.js:

• Event Loop: Handles asynchronous operations.

• Modules: Built-in (fs, http) and custom modules.

• npm Packages: Managing dependencies using package.json.

Introduction to Express:

• What is Express? A minimal and flexible Node.js web application framework.

• Features:

  • Simplifies routing and middleware management.

  • Facilitates REST API development.

  • Easily integrates with databases.

2. Building Web Applications with Express:

Setting Up an Express Application:

1. Initialize Node Project:

   mkdir express-app && cd express-app
   npm init -y
   npm install express

2. Create a Basic Server:

   • Create index.js:

     const express = require('express');
     const app = express();
     const PORT = 3000;
     
     app.get('/', (req, res) => {
       res.send('Hello, World!');
     });
     
     app.listen(PORT, () => {
       console.log(`Server running on http://localhost:${PORT}`);
     });

3. Run the Server:

   node index.js

   • Visit http://localhost:3000 in your browser to see "Hello, World!"

Routing in Express:

• Define Routes:

  app.get('/about', (req, res) => {
    res.send('About Page');
  });
  
  app.post('/contact', (req, res) => {
    res.send('Contact Form Submitted');
  });

Middleware in Express:

• Using Middleware:

  app.use(express.json());  // To parse JSON bodies
  app.use((req, res, next) => {
    console.log(`${req.method} request for '${req.url}'`);
    next();
  });

3. REST API Development with Express:

Create a Simple REST API:

1. Sample Data:

   let users = [
     { id: 1, name: 'Alice' },
     { id: 2, name: 'Bob' },
   ];

2. CRUD Operations:

   • GET (Retrieve All Users):

     app.get('/users', (req, res) => {
       res.json(users);
     });

   • GET (Retrieve Single User):

     app.get('/users/:id', (req, res) => {
       const user = users.find(u => u.id == req.params.id);
       if (user) res.json(user);
       else res.status(404).send('User not found');
     });

   • POST (Add New User):

     app.post('/users', (req, res) => {
       const newUser = { id: users.length + 1, ...req.body };
       users.push(newUser);
       res.status(201).json(newUser);
     });

   • PUT (Update User):

     app.put('/users/:id', (req, res) => {
       const index = users.findIndex(u => u.id == req.params.id);
       if (index !== -1) {
         users[index] = { id: parseInt(req.params.id), ...req.body };
         res.json(users[index]);
       } else res.status(404).send('User not found');
     });

   • DELETE (Remove User):

     app.delete('/users/:id', (req, res) => {
       users = users.filter(u => u.id != req.params.id);
       res.status(204).send();
     });