Prerequisites

Before installing Express, make sure you have Node.js installed on your system:

node --version   # v18 or higher recommended
npm --version    # Comes with Node.js

If you don’t have Node.js, download it from nodejs.org.

Step 1: Create a Project Directory

mkdir my-express-app
cd my-express-app

Step 2: Initialize package.json

npm init -y

The -y flag accepts all defaults. This creates a package.json file:

{
  "name": "my-express-app",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "keywords": [],
  "author": "",
  "license": "ISC"
}

Step 3: Install Express

npm install express

This does three things:

1. Downloads Express and its dependencies into node_modules/
2. Adds express to the dependencies field in package.json
3. Creates package-lock.json (locks exact versions)

"dependencies": {
  "express": "^4.21.0"
}

The caret ^ means npm will auto-update to minor/patch versions.

Step 4: Create the Entry File

Create index.js (or app.js / server.js) as your main application file:

touch index.js

Step 5: Project Structure

Your folder should now look like this:

my-express-app/
├── node_modules/       # Installed packages (auto-generated)
├── index.js            # Main application file
├── package.json        # Project metadata and dependencies
└── package-lock.json   # Locked dependency versions

Installing Nodemon (Development Tool)

Nodemon automatically restarts your server when file changes are detected:

npm install --save-dev nodemon

Update package.json scripts:

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

Now you can run npm run dev during development for auto-restart.

Understanding node_modules

• node_modules/ contains all installed packages
• Never commit it to version control - add it to .gitignore
• It can be reinstalled anytime with npm install
• Always commit package.json and package-lock.json

.gitignore:

node_modules/
.env

Express Dependencies

When you install Express, npm also installs its dependencies:

express
├── accepts              # Content negotiation
├── array-flatten        # Array flattening
├── body-parser          # Request body parsing (built-in)
├── content-disposition  # Content-Disposition header
├── cookie-signature     # Cookie signing
├── debug                # Debug logging
├── depd                 # Deprecation warnings
├── encodeurl            # URL encoding
├── escape-html          # HTML escaping
├── finalhandler         # Final request handler
├── fresh                # HTTP freshness check
├── merge-descriptors    # Merge property descriptors
├── methods              # HTTP methods list
├── on-finished          # Request completion listener
├── parseurl             # URL parsing
├── path-to-regexp       # Path pattern matching
├── proxy-addr           # Proxy address detection
├── qs                   # Query string parser
├── range-parser         # Range header parser
├── safe-buffer          # Buffer safety
├── send                 # File streaming
├── serve-static         # Static file serving
├── setprototypeof       # Prototype assignment
├── statuses             # HTTP status codes
├── type-is              # Content-type checking
├── utils-merge          # Object merging
└── vary                 # Vary header handling

Version Checking

To verify your Express installation:

npm list express
# my-express-app@1.0.0 /path/to/my-express-app
# └── express@4.21.0

Or in Node.js code:

console.log(require('express/package.json').version);

Common Setup Issues

Issue	Fix
command not found: node	Install Node.js from nodejs.org
EACCES permission error	Use nvm to manage Node versions
npm ERR! network error	Check internet/proxy settings
Module not found	Run npm install in the project root

Key Takeaways

• Initialize a project with npm init -y
• Install Express with npm install express
• Use nodemon for development with npm install --save-dev nodemon
• Add node_modules/ to .gitignore
• Verify installation with node -e "require('express')"