Getting Started with Express

Summary

Express.js is a popular web framework for Node.js that simplifies building web applications and APIs. This tutorial will walk you through creating your first Express application from scratch.

You'll learn the basic steps to set up a new project, install dependencies, write server code, and run your application locally.

Key Vocabulary

Express.js: A minimal and flexible Node.js web application framework

Node.js: A JavaScript runtime for server-side development

npm: Node Package Manager for installing and managing JavaScript packages

Route: A path that defines how an application responds to client requests

Port: A network port number where the server listens for connections

Prerequisites

Node.js installed on your system
npm installed
Basic command line knowledge
A text editor

Step-by-Step Instructions

Step 1

Create Project Directory

Create a new directory for your Express app.

mkdir my-express-app

Why this works: Creates a folder to hold your project files.

Step 2

Navigate to Project Directory

Change to the newly created directory.

cd my-express-app

Why this works: Moves you into the project folder to work with the files.

Step 3

Initialize npm Project

Set up a new npm project.

npm init -y

Why this works: Creates a package.json file with default settings for your project.

Step 4

Install Express

Install the Express framework.

npm install express

Why this works: Downloads and installs Express.js as a dependency.

Step 5

Create Application Code

Write the main server code.

// Import the Express framework
const express = require('express');

// Create an instance of an Express application
const app = express();

// Define the port number where the server will listen for requests
const PORT = 3000;

// Define a route for the root URL ('/') that sends a welcome message
app.get('/', (req, res) => {
  // Send a response to the client with a welcome message
  res.send('Welcome to your first Express app!');
});

// Start the server and listen for incoming requests on the specified port
app.listen(PORT, () => {
  // Log a message to the console indicating the server is running
  console.log(`Server running at http://localhost:${PORT}`);
});

Why this works: This code sets up an Express server with a basic route and starts listening on port 3000.

Step 6

Start the Server

Run the application.

node app.js

Why this works: Executes the app.js file to start the server.

Common Issues & Solutions

Problem: Command not found error
Solution: Ensure Node.js and npm are installed and in your PATH.

Problem: Port already in use
Solution: Change the PORT variable to a different number or stop the conflicting process.

Problem: Cannot connect to server
Solution: Check that the server started successfully and visit http://localhost:3000.

Conclusion

You've successfully created and run your first Express.js application!

The server is now running and you can visit http://localhost:3000 to see your app in action.

This is just the beginning - you can now add more routes, middleware, and features to build more complex applications.