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Introduction

This tutorial will walk you through creating a basic Express application from scratch. By the end, you’ll understand the fundamentals of Express and have a working web server.
This tutorial assumes you have Node.js 18 or higher installed. If not, visit the Installation guide first.

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Project Setup

1

Create project directory

Create a new directory for your Hello World application:
mkdir express-hello-world
cd express-hello-world
2

Initialize Node.js project

Create a package.json file to manage your project dependencies:
npm init -y
This creates a basic package.json with default values.
3

Install Express

Install Express as a project dependency:
npm install express

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Creating Your First Server

1

Create the main file

Create a file named index.js in your project root:
touch index.js
2

Import Express

Open index.js in your text editor and import Express:
index.js
const express = require('express')
This imports the Express module into your application.
3

Create Express application

Create an instance of an Express application:
index.js
const express = require('express')
const app = express()
The app object has methods for routing HTTP requests, configuring middleware, rendering HTML views, and more.
4

Define a route

Add a route handler for the root path:
index.js
const express = require('express')
const app = express()

app.get('/', (req, res) => {
  res.send('Hello World')
})
This tells Express to respond with “Hello World” when a GET request is made to the root URL (/).
  • req (request) - contains information about the HTTP request
  • res (response) - used to send a response back to the client
5

Start the server

Add code to start the server on a specific port:
index.js
const express = require('express')
const app = express()

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

app.listen(3000, () => {
  console.log('Express started on port 3000')
})
The listen() method binds the application to port 3000 and starts listening for connections.

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Running Your Application

1

Start the server

Run your application using Node.js:
node index.js
You should see the console message:
Express started on port 3000
2

Test in browser

Open your web browser and navigate to:
http://localhost:3000
You should see “Hello World” displayed in your browser.
3

Test with curl (optional)

Alternatively, test using curl from another terminal:
curl http://localhost:3000
Output:
Hello World
To stop the server, press Ctrl+C in the terminal where it’s running.

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Understanding the Code

Let’s break down what each part of your Hello World application does:

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Importing Express

const express = require('express')
This line imports the Express module. Express is a function that, when called, creates a new application.

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Creating the Application

const app = express()
This creates a new Express application instance. The app object represents your web application and provides methods for:
  • Routing HTTP requests
  • Configuring middleware
  • Rendering views
  • Setting application properties

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Defining Routes

app.get('/', (req, res) => {
  res.send('Hello World')
})
This defines a route handler for GET requests to the root path (/). When a user visits http://localhost:3000/, this function executes.
  • app.get() - handles HTTP GET requests
  • '/' - the URL path to match
  • (req, res) => {...} - callback function executed when the route matches
  • res.send() - sends the response back to the client

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Starting the Server

app.listen(3000, () => {
  console.log('Express started on port 3000')
})
This starts the server and tells it to listen for incoming requests on port 3000. The callback function runs once the server starts successfully.

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Expanding Your Application

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Adding More Routes

You can add multiple routes to handle different URLs:
index.js
const express = require('express')
const app = express()

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

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

app.get('/contact', (req, res) => {
  res.send('Contact page')
})

app.listen(3000, () => {
  console.log('Express started on port 3000')
})
Now you can visit:
  • http://localhost:3000/ - displays “Hello World”
  • http://localhost:3000/about - displays “About page”
  • http://localhost:3000/contact - displays “Contact page”

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Sending JSON Responses

For API endpoints, you can send JSON instead of plain text:
index.js
app.get('/api/hello', (req, res) => {
  res.json({
    message: 'Hello World',
    timestamp: new Date().toISOString()
  })
})
Test it: 
curl http://localhost:3000/api/hello
Output: 
{
  "message": "Hello World",
  "timestamp": "2026-03-01T12:00:00.000Z"
}

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Using Route Parameters

Capture dynamic values from URLs using route parameters:
index.js
app.get('/user/:id', (req, res) => {
  const userId = req.params.id
  res.send(`User ID: ${userId}`)
})
Test it: 
curl http://localhost:3000/user/123
# Output: User ID: 123

curl http://localhost:3000/user/abc
# Output: User ID: abc

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Handling Different HTTP Methods

Express supports all HTTP methods:
index.js
const express = require('express')
const app = express()

// Parse JSON request bodies
app.use(express.json())

// GET request
app.get('/api/data', (req, res) => {
  res.json({ method: 'GET' })
})

// POST request
app.post('/api/data', (req, res) => {
  res.json({ method: 'POST', data: req.body })
})

// PUT request
app.put('/api/data/:id', (req, res) => {
  res.json({ method: 'PUT', id: req.params.id })
})

// DELETE request
app.delete('/api/data/:id', (req, res) => {
  res.json({ method: 'DELETE', id: req.params.id })
})

app.listen(3000, () => {
  console.log('Express started on port 3000')
})

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Best Practices

Instead of hardcoding the port, use environment variables:
const port = process.env.PORT || 3000

app.listen(port, () => {
  console.log(`Express started on port ${port}`)
})
Always include error handling middleware:
app.use((err, req, res, next) => {
  console.error(err.stack)
  res.status(500).send('Something went wrong!')
})
Install nodemon to automatically restart your server when files change:
npm install --save-dev nodemon
Add to package.json:
{
  "scripts": {
    "start": "node index.js",
    "dev": "nodemon index.js"
  }
}
Run with: npm run dev

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Complete Example

Here’s the complete Hello World application with all the features discussed:
index.js
const express = require('express')
const app = express()
const port = process.env.PORT || 3000

// Middleware
app.use(express.json())

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

app.get('/api/hello', (req, res) => {
  res.json({
    message: 'Hello World',
    timestamp: new Date().toISOString()
  })
})

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

// 404 handler
app.use((req, res) => {
  res.status(404).send('Page not found')
})

// Error handler
app.use((err, req, res, next) => {
  console.error(err.stack)
  res.status(500).send('Internal server error')
})

// Start server
app.listen(port, () => {
  console.log(`Express started on port ${port}`)
})

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Next Steps

Now that you’ve built your first Express application, explore these topics:

Routing

Learn advanced routing techniques and patterns

Middleware

Understand how middleware works in Express

Template Engines

Render dynamic HTML using template engines

Error Handling

Implement robust error handling strategies

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