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Introduction to Express.js

Express.js, commonly referred to as Express, is a minimal and flexible Node.js web application framework that provides a robust set of features for web and mobile applications. It's designed to build web applications and APIs quickly and efficiently.

Key Features of Express:​

  1. Routing: Express makes it easy to define routes for your application. Routes are used to map specific HTTP methods and URLs to functions that handle them.

  2. Middleware: Middleware functions are a powerful feature of Express. They can be used to perform tasks before the request reaches its final handler. This can include tasks like authentication, logging, and data parsing.

  3. Templating: Express allows you to use various template engines like EJS, Pug, or Handlebars to dynamically generate HTML.

  4. Static Files: You can serve static files (like HTML, CSS, and JavaScript) using Express, making it ideal for building single-page applications and static websites.

  5. Error Handling: Express provides a clean and effective way to handle errors in your application.

Installing Express​

Before you can use Express, you need to install it. You can install Express using npm (Node Package Manager). Open your terminal and run:

npm install express

Creating a Simple Express Application​

Let's create a basic Express application and see how it works. First, create a file, for example, app.js. Then, add the following code:

app.js
const express = require('express');
const app = express();
const port = 3000;

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

// Start the server
app.listen(port, () => {
  console.log(`Server is running on port ${port}`);
});

In this example, we:

  • Import the Express module.
  • Create an Express application.
  • Define a route for the root URL ('/').
  • Use the app.get method to handle HTTP GET requests.
  • Send a response of "Hello, Express!" when someone accesses the root URL.
  • Start the server on port 3000.

To run this application, use the following command:

node app.js

Now, if you open a web browser and go to http://localhost:3000, you'll see "Hello, Express!" displayed in your browser.

http://localhost:3000

Hello, Express!

This is a simple example, but it demonstrates the basics of creating an Express application and defining routes. You can build on this foundation to create more complex web applications and APIs.