Express.js is a popular and lightweight framework for building web applications using JavaScript. It simplifies the process of creating routes, handling requests, and managing middleware. Whether you’re building a simple blog or a complex API, Express.js provides the tools you need to get started quickly.
What is Express.js?
Express.js is an open-source web framework for Node.js. It is designed to make it easy to build web applications by providing a set of features and conventions. Express.js is often used for building RESTful APIs, single-page applications, and web apps that require server-side rendering.
Setting Up Your Environment
Before you can start using Express.js, you need to have Node.js and npm (Node Package Manager) installed on your computer. You can download Node.js from the official website, which will include npm.
Once you have Node.js installed, you can create a new project directory and initialize it with npm:
mkdir my-express-app
cd my-express-app
npm init -y
This will create a package.json file in your project directory. Next, install Express.js as a dependency:
npm install express
Creating a Basic Server
Now that you have Express.js installed, you can create a simple server. Create a new file called app.js and add the following code:
const express = require('express');
const app = express();
const port = 3000;
app.get('/', (req, res) => {
res.send('Hello World!');
});
app.listen(port, () => {
console.log(`Server running at http://localhost:${port}`);
});
This code imports Express.js, creates an instance of the Express application, defines a route for the root URL (/), and starts the server on port 3000. When you run the server using node app.js, you should see the message Hello World! when you visit http://localhost:3000 in your browser.
Routing in Express.js
Express.js uses routes to handle different HTTP requests. The most common HTTP methods are GET, POST, PUT, and DELETE. Each route can have a corresponding handler function that determines what happens when a request is made to that route.
GET Requests
A GET request is used to retrieve data from the server. For example, to display a list of users, you might have a route like this:
app.get('/users', (req, res) => {
res.send('List of users');
});
POST Requests
A POST request is used to send data to the server. For example, to create a new user, you might have a route like this:
app.post('/users', (req, res) => {
res.send('User created');
});
PUT Requests
A PUT request is used to update existing data on the server. For example, to update a user’s information, you might have a route like this:
app.put('/users/:id', (req, res) => {
res.send(`User ${req.params.id} updated`);
});
DELETE Requests
A DELETE request is used to delete data from the server. For example, to delete a user, you might have a route like this:
app.delete('/users/:id', (req, res) => {
res.send(`User ${req.params.id} deleted`);
});
Middleware in Express.js
Middleware functions are functions that have access to the request object (req), the response object (res), and the next middleware function in the application’s request-response cycle. Middleware can perform tasks such as logging, parsing the request body, and handling authentication.
Built-in Middleware
Express.js comes with several built-in middleware functions that you can use in your application. Some of the most commonly used middleware functions include:
express.json(): Parses the request body as JSON.express.urlencoded(): Parses the request body as URL-encoded data.express.static(): Serves static files from a directory.
Custom Middleware
You can also create your own middleware functions to perform specific tasks. For example, you might create a middleware function to log the details of each request:
app.use((req, res, next) => {
console.log(`Request received at ${new Date().toISOString()}`);
next();
});
This middleware function logs the time and date when each request is received and then calls next() to pass control to the next middleware function or route handler.
Templating Engines
Express.js supports several templating engines that allow you to create dynamic web pages. Some popular templating engines include EJS, Pug, and Handlebars.
Using EJS
EJS (Embedded JavaScript) is a templating engine that allows you to embed JavaScript code within HTML templates. To use EJS with Express.js, you need to install the ejs package:
npm install ejs
Then, you can set up EJS as the templating engine in your Express.js application:
const express = require('express');
const app = express();
app.set('view engine', 'ejs');
app.get('/', (req, res) => {
res.render('index', { title: 'Home Page' });
});
In this example, the index.ejs template would be located in a views directory. The template might look like this:
<!DOCTYPE html>
<html>
<head>
<title><%= title %></title>
</head>
<body>
<h1>Welcome to the Home Page!</h1>
</body>
</html>
Using Pug
Pug is another popular templating engine that uses a syntax similar to HAML. To use Pug with Express.js, you need to install the pug package:
npm install pug
Then, you can set up Pug as the templating engine in your Express.js application:
const express = require('express');
const app = express();
app.set('view engine', 'pug');
app.get('/', (req, res) => {
res.render('index', { title: 'Home Page' });
});
The index.pug template might look like this:
html
head
title= title
body
h1 Welcome to the Home Page!
Frequently Asked Questions
Q: What is the difference between Express.js and other web frameworks like Django or Ruby on Rails?
A: Express.js is a lightweight framework that provides minimal functionality out of the box. This allows developers to choose the tools and libraries they want to use. In contrast, frameworks like Django and Ruby on Rails provide a more opinionated structure and include many features out of the box.
Q: Can I use Express.js to build a RESTful API?
A: Yes, Express.js is commonly used to build RESTful APIs. It provides features like routing, middleware, and request handling that are essential for building APIs.
Q: How do I handle errors in Express.js?
A: Express.js provides an error-handling middleware that can be used to catch and handle errors. You can define an error-handling middleware function that takes an error object as the first parameter.
Q: Is Express.js scalable?
A: Yes, Express.js is scalable. It is commonly used in production environments and can handle large amounts of traffic. However, scalability depends on how your application is designed and configured.
Q: How do I secure an Express.js application?
A: Securing an Express.js application involves several best practices, such as using HTTPS, validating user input, sanitizing outputs, and using secure cookies. Express.js also supports middleware like Helmet, which provides various security-related HTTP headers.
Q: Can I use Express.js with other databases?
A: Yes, Express.js can be used with various databases, including MongoDB, MySQL, PostgreSQL, and more. You can use ORM (Object-Relational Mapping) libraries like Sequelize or Mongoose to interact with databases.
Q: How do I deploy an Express.js application?
A: Express.js applications can be deployed to various cloud platforms like Heroku, AWS, Google Cloud, and others. You can also deploy your application using a containerization tool like Docker.
Conclusion
Express.js is a powerful and flexible framework for building web applications and APIs using JavaScript. By leveraging its routing, middleware, and templating features, you can create efficient and scalable applications. Whether you’re building a simple blog or a complex API, Express.js provides the tools you need to get started quickly. With its extensive ecosystem and active community, Express.js remains a popular choice for developers.