ExpressJS – Web framework for Node.js

Introduction

Express.js is a fast, unopinionated, and minimalist web framework for Node.js that simplifies the process of building web applications and APIs. As one of the most popular backend frameworks, Express.js provides developers with a robust set of features to create scalable and efficient web applications with minimal effort.

This article covers everything you need to know about Express.js, including its features, installation, setup, middleware, routing, database integration, error handling, and advanced concepts.

What is Express.js?

Express.js is a web application framework for Node.js that provides a simple way to manage routes, handle requests and responses, and integrate with databases. It serves as the foundation for many popular web applications, including RESTful APIs and full-stack applications using frameworks like React, Angular, or Vue.js.

Key Features

1. Minimalist Framework – Provides only the essential tools, allowing developers to build applications with flexibility.
2. Middleware Support – Easily add functions for request handling, authentication, logging, etc.
3. Routing System – Manage HTTP routes efficiently.
4. Template Engines – Supports Pug, EJS, Handlebars, etc., for rendering dynamic views.
5. RESTful API Support – Ideal for building APIs with JSON responses.
6. Error Handling – Provides built-in and custom error-handling mechanisms.
7. Integration with Databases – Works with MongoDB, MySQL, PostgreSQL, etc.
8. Scalability – Suitable for both small applications and large-scale enterprise solutions.

Installing Express.js

To start using Express.js, ensure you have Node.js installed. Then, follow these steps:

Step 1: Initialize a Node.js Project

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

This creates a package.json file for managing dependencies.

Step 2: Install Express.js

npm install express

Now, Express.js is ready to use in your project.

Creating a Basic Express.js Server

Create a file server.js and add the following code:

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

app.get('/', (req, res) => {
    res.send('Hello, Express!');
});

app.listen(PORT, () => {
    console.log(`Server is running on http://localhost:${PORT}`);
});

Running the Server

node server.js

Visit http://localhost:3000/ in your browser, and you should see “Hello, Express!”.

Routing in Express.js

Express.js provides a simple way to define routes for different HTTP methods.

Defining Routes

app.get('/about', (req, res) => {
    res.send('About Page');
});

app.post('/submit', (req, res) => {
    res.send('Form Submitted');
});

Route Parameters

app.get('/user/:id', (req, res) => {
    res.send(`User ID: ${req.params.id}`);
});

Accessing /user/123 will return “User ID: 123”.

Middleware in Express.js

Middleware functions process requests before reaching the final handler.

Built-in Middleware

app.use(express.json());
app.use(express.urlencoded({ extended: true }));

Custom Middleware

app.use((req, res, next) => {
    console.log(`Request URL: ${req.url}`);
    next();
});

Handling Forms and JSON Data

Express.js allows processing form data and JSON using middleware.

Parsing JSON Data

app.use(express.json());

app.post('/data', (req, res) => {
    res.json(req.body);
});

Handling Form Data

app.use(express.urlencoded({ extended: true }));

app.post('/submit', (req, res) => {
    res.send(`Received: ${req.body.name}`);
});

Connecting Express.js to a Database

Express.js works with various databases. Below is an example of connecting it to MongoDB using Mongoose.

Install Mongoose

npm install mongoose

Connecting to MongoDB

const mongoose = require('mongoose');
mongoose.connect('mongodb://localhost:27017/mydatabase', {
    useNewUrlParser: true,
    useUnifiedTopology: true,
})
.then(() => console.log('Connected to MongoDB'))
.catch(err => console.log(err));

Error Handling in Express.js

Express provides a way to handle errors effectively.

Simple Error Handling

app.use((req, res, next) => {
    res.status(404).send('Page Not Found');
});

Centralized Error Handler

app.use((err, req, res, next) => {
    console.error(err.stack);
    res.status(500).send('Something went wrong!');
});

Advanced Topics

1. Using Template Engines

Express.js supports template engines like Pug and EJS.

npm install ejs

app.set('view engine', 'ejs');
app.get('/dashboard', (req, res) => {
    res.render('dashboard', { username: 'JohnDoe' });
});

2. Building a RESTful API

Express.js is commonly used for building RESTful APIs.

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

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

3. Authentication with JWT

npm install jsonwebtoken bcryptjs

const jwt = require('jsonwebtoken');
const bcrypt = require('bcryptjs');

app.post('/login', async (req, res) => {
    const token = jwt.sign({ userId: 123 }, 'secretKey', { expiresIn: '1h' });
    res.json({ token });
});

Conclusion

Express.js is a powerful yet simple framework for building web applications and APIs with Node.js. Its flexibility, ease of use, and vast ecosystem make it the go-to choice for developers. Whether you’re building a small website or a large-scale API, Express.js provides the necessary tools to streamline development.

Useful Links

• Official Express.js Documentation
• GitHub Repository

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