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Getting Started with Express.js ​

Express.js is a fast, unopinionated, minimalist web framework for Node.js. In this tutorial, you'll learn how to set up your first Express application.

Installation ​

Prerequisites ​

Make sure you have Node.js installed:

bash
node --version  # Should be v14 or higher
npm --version

Creating a New Project ​

bash
# Create project directory
mkdir express-tutorial
cd express-tutorial

# Initialize package.json
npm init -y

# Install Express
npm install express

Your First Express Server ​

Create a file called index.js:

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

// Define a route
app.get('/', (req, res) => {
  res.send('Hello World!');
});

// Start the server
app.listen(port, () => {
  console.log(`Server running at http://localhost:${port}`);
});

Run your server:

bash
node index.js

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

Understanding the Code ​

Let's break down what each part does:

1. Import Express ​

javascript
const express = require('express');

This imports the Express module.

2. Create an Application ​

javascript
const app = express();

This creates an Express application instance. The app object has methods for:

  • Routing HTTP requests
  • Configuring middleware
  • Rendering HTML views
  • Registering template engines

3. Define Routes ​

javascript
app.get('/', (req, res) => {
  res.send('Hello World!');
});
  • app.get() - Handles GET requests
  • '/' - The URL path
  • req - Request object (incoming data)
  • res - Response object (outgoing data)
  • res.send() - Sends a response to the client

4. Start Listening ​

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

This starts the server on the specified port.

HTTP Methods ​

Express provides methods for all HTTP verbs:

javascript
// GET - Retrieve data
app.get('/users', (req, res) => {
  res.send('Get all users');
});

// POST - Create data
app.post('/users', (req, res) => {
  res.send('Create a user');
});

// PUT - Update data (full replacement)
app.put('/users/:id', (req, res) => {
  res.send('Update user');
});

// PATCH - Update data (partial)
app.patch('/users/:id', (req, res) => {
  res.send('Partial update');
});

// DELETE - Remove data
app.delete('/users/:id', (req, res) => {
  res.send('Delete user');
});

Response Methods ​

Express provides several ways to send responses:

javascript
// Send string
res.send('Hello');

// Send JSON
res.json({ message: 'Hello', status: 'success' });

// Send status code
res.sendStatus(200); // OK
res.sendStatus(404); // Not Found

// Send status with message
res.status(201).json({ message: 'Created' });

// Redirect
res.redirect('/login');

// Send file
res.sendFile('/path/to/file.pdf');

// Download file
res.download('/path/to/file.pdf');

Using ES Modules ​

You can use modern ES module syntax:

json
// package.json
{
  "type": "module"
}
javascript
// index.js
import express from 'express';

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

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

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

Development with Nodemon ​

Nodemon automatically restarts your server when files change:

bash
# Install nodemon
npm install --save-dev nodemon

Update package.json:

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

Now run with:

bash
npm run dev

Project Structure ​

For larger applications, organize your code:

express-tutorial/
├── node_modules/
├── src/
│   ├── routes/
│   │   └── index.js
│   ├── controllers/
│   │   └── userController.js
│   ├── middleware/
│   │   └── auth.js
│   └── app.js
├── package.json
└── index.js

Environment Variables ​

Use environment variables for configuration:

bash
npm install dotenv

Create .env file:

env
PORT=3000
NODE_ENV=development

Load in your app:

javascript
require('dotenv').config();

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

app.listen(port, () => {
  console.log(`Server running in ${env} mode on port ${port}`);
});

WARNING

Never commit .env files to version control. Add them to .gitignore.

Summary ​

In this tutorial, you learned:

  • How to install Express.js
  • Creating a basic server
  • HTTP methods (GET, POST, PUT, DELETE)
  • Different response methods
  • Using ES modules
  • Development workflow with nodemon
  • Environment variables

Next, we'll explore Routing in depth.