Node.JS & Express

What is NodeJS

• A runtime environment that allows users to run javascript outside the browser, mainly on servers.

• Used to build fast, scalable network applications.

• Ideal for APIs, real-time apps and servers.

Why NodeJS is fast and efficient

It uses an event-driven, non-blocking IO model that makes it lightweight and efficient

Event-driven

Reacts to requests, file reads, timeouts

Non-blocking I/O

I/O doesn’t wait for slow operations to finish.

Lightweight and efficient

Handles many users with fewer resources

Features of NodeJS

• Asynchronous and event-driven

• Very fast

• Single threaded

• No buffering

Asynchronous and event driven

Operations like file reads, timers and database queries run asynchronously.

Very fast

• Uses the V8 engine, which translates JavaScript code to machine code.

• Minimal overhead for handling requests.

Single-threaded

• One main thread

• Each request is stacked on top of each other instead of generating a new thread per request.

• This makes it memory-efficient and scalable

No buffering

• Data is processed in streams

• Reduces memory usage

What is NodeJS used for

• Generate dynamic page content

• CRUD files on server

• Collect form data

• Build REST APIs

How to create server using NodeJS

1. Import required modules

2. Start server

3. Add listener

Import required modules

const http = require(‘http‘);

const port = process.env.PORT || 3000;

Start server

const server = http.createServer((res, req)=> {

res.writeHead(200, “Content-type“: “text/plain“);

res.end('Hello world!')

});

Add listener

server.listen(port);

What is express

• Web application framework for NodeJS

• Acts as middleware between client and server, handling data flow between them.

Why is Express good

• Structure: provides a standard way to organise web applications.

• Productivity: removes boilerplate (like manual URL parsing)

• Tools: offers pre-built libraries for handling requests, routing and connecting to databases.

Features of Express

• Allows to set up middleware to respond to HTTP requests.

• Allows to dynamically render HTML pages based on passing arguments to template.

• Define a routing table which is used to perform different actions based on an HTTP method and URL.

Basic express application

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

app.get(‘/‘, (res, req) => {
   res.send(<h1>Home Page</1>“);
});

listen(3000);

Middleware function

• A function that runs between the request and the response.

• They have acces to:

  • req

  • res

  • next

What middleware functions do

• Execute any code

• Modify the request and response object

• End request-response cycle

• Call the next middleware function in the stack.

Types of middleware functions

• Route handler

• Logging middleware

• Error handler

Route handler

app.get(‘/path‘, (req, res) => {
   res.send(“Home Page“)
});

Logger Middleware

app.use((req, res, next) => {
   console.log("Log something");
   next();
});

Error handler

app.use((err, req, res, next) => {
   console.log(err.stack);
   res.status(500).send("Something Broke");
})

Request Object

• Represents the HTTP request

• Contains information about the body, headers, parameters

Request Object methods

• req.body

• req.headers

• req.params

• req.query

Response Object

• Represents the HTTP response that the Express app sends when it receives a request.

Response Object methods

• res.send(body)

• res.json(json)

• res.status(code)

• res.redirect(path)

• res.render(view, locals)

Express Router

• A mini version of an Express application that handles routes, has its own middleware and can be exported and reused.

• Routers break down the application into mini-apps

Express body parsing

const bodyParser = require('body-parser');
app.use(bodyParser.urlencoded({extended=false}));

app.post('/submit', (req, res) => {
   console.log(req.body) // form data is here
   res.redirect(/);
});

Express serving static files

const path = require('path');
app.use(express.static('folder'));