Express Setup and Basics

Express is the most popular Node.js web framework. It provides a thin layer of features on top of Node's built-in http module, making it fast and straightforward to build web applications and APIs.

Installing Express

Start a new project and install Express:

mkdir my-api && cd my-api
npm init -y
npm install express
npm install -D nodemon

Add a dev script to package.json:

{
  "scripts": {
    "start": "node src/app.js",
    "dev": "nodemon src/app.js"
  }
}

Your First Express Server

Run it with npm run dev and visit http://localhost:3000 in your browser.

Understanding Request and Response

Every route handler receives req (request) and res (response) objects.

The Request Object

The Response Object

Parsing Request Bodies

Express does not parse request bodies by default. Add the built-in middleware:

Project Structure

Organize your code as the project grows:

my-api/
├── src/
│   ├── app.js            # Express app setup
│   ├── server.js          # Server startup
│   ├── routes/
│   │   ├── users.js       # User routes
│   │   └── posts.js       # Post routes
│   ├── controllers/
│   │   ├── userController.js
│   │   └── postController.js
│   ├── middleware/
│   │   ├── auth.js
│   │   └── errorHandler.js
│   └── config/
│       └── index.js       # Configuration
├── package.json
└── .env

Separating App and Server

This separation makes your app easier to test because you can import app without starting the server.

Route Organization

Extract routes into separate files:

Configuration Module

Centralize your configuration:

Error Handling

Add a global error handler:

Register it after all routes:

Practical Exercise

Set up a complete Express project with proper structure:

Key Takeaways

• Express adds routing, middleware, and convenience methods on top of Node's http module.
• Use express.json() middleware to parse JSON request bodies.
• Separate your app setup from server startup for testability.
• Organize routes into separate files using express.Router().
• Always add a global error handler as the last middleware.