Express.js for JavaScript (Node.js): Complete Guide with Examples

What is Express.js and why is it needed?

Express.js is a minimal and flexible web framework for Node.js, written in JavaScript. It provides developers with a powerful set of tools for creating web applications and APIs (REST, GraphQL). Express.js is the de facto standard for server-side development on Node.js due to its simplicity, speed, and huge community.

Why is Express.js needed? Node.js itself provides a low-level HTTP module that allows you to create servers. However, working with it directly requires writing a lot of boilerplate code for handling routes, parsing requests, managing sessions, etc. Express.js solves these problems by providing:

• Routing: Simple definition of handlers for different URLs and HTTP methods (GET, POST, PUT, DELETE).
• Middleware: A powerful system that allows you to execute code before or after processing a request (e.g., for logging, authentication, compression).
• Request and Response Management: Convenient methods for working with URL parameters, request body, cookies, headers, and sending responses (JSON, HTML, files).
• Templating: Integration with popular template engines such as Pug, EJS, Handlebars.
• Static Files: Simple serving of static resources (CSS, JS, images).

Express.js is used to create everything from simple single-page applications to complex enterprise systems and high-load APIs.

Installing Express.js

Installing Express.js is done via the npm (Node Package Manager) package manager. It is assumed that you already have Node.js and npm installed.

Step 1: Initialize the project

Create a new directory for your project and navigate to it in the terminal. Then initialize a new Node.js project:

mkdir my-express-appcd my-express-appnpm init -y

The -y flag automatically accepts all default values. You can also omit it to manually fill in the project metadata.

Step 2: Install Express

Install Express.js as a project dependency:

npm install express

This command will add Express to the package.json file in the dependencies section and create a node_modules folder with the library itself and its dependencies.

Step 3: Verify installation

After installation, you can check the version of Express in your project:

npx express --version

Or simply look in the package.json file.

Quick Start: "Hello World" on Express.js

Create a file app.js (or index.js) in the root of your project and add the following code:

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

// Define a route for the root URLapp.get('/', (req, res) => {  res.send('Hello World! Express.js is working!');});

// Start the serverapp.listen(port, () => {  console.log(`Server running at http://localhost:${port}`);});

Running the application:

In the terminal, run the command:

node app.js

Open your browser and go to http://localhost:3000. You should see the message "Hello World! Express.js is working!".

What is happening here?

1. require('express') — import the Express library.
2. express() — create an instance of the Express application.
3. app.get('/', callback)

   Also in library

   Swagger/OpenAPI Generation for C# (.NET): Swashbuckle and NSwag ent for Go: Complete Guide with Examples Awaitility Java Guide: Complete Tutorial with Examples node-cron: Task Scheduler for JavaScript (Node.js) Flow for Kotlin: Complete Guide with Examples