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Welcome to this tutorial on Express.js – a powerful web application framework for Node.js. Whether you're a beginner or an experienced developer, Express.js can make building web applications a breeze. So, let's dive in and explore the wonderful world of Express.js!

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What is Express.js?

Express.js is a minimalistic, fast, and unopinionated web application framework for Node.js. It provides a robust set of features and utilities that make building web applications with Node.js a lot easier. Express.js allows you to handle routes, manage middleware, handle requests and responses, and so much more, all in a simple and elegant manner.

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Getting Started with Express.js

To begin, you'll need to set up a new Node.js project and install the Express.js package. Open your terminal and navigate to your project directory.

1. Setting Up a New Node.js Project

Let's start by initializing a new Node.js project. Run the following command in your project directory:

This will create a package.json file that will hold information about your project and its dependencies.

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2. Installing Express.js

Now, let's install Express.js. In your terminal, run the following command:

This will install the Express.js package and its dependencies in your project.

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Working with Express.js

With Express.js installed, you're ready to start building web applications. Let's explore some key concepts and features of Express.js.

1. Creating an Express Application

To create an Express application, create a new JavaScript file, e.g., app.js, and require the Express module at the top of the file:

Here, we've imported the Express module and created an instance of the Express application.

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2. Handling Routes

One of the fundamental aspects of Express.js is handling routes. You can define routes using the app object and handle HTTP methods such as GET, POST, PUT, DELETE, etc.

In this example, we've defined a route using app.get(). Whenever a GET request is made to the root URL ('/'), the callback function is executed, and we send the response 'Hello, Express!' back to the client.

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3. Middleware

Middleware functions in Express.js allow you to process requests and modify the response before sending it back to the client. Middleware functions are executed in the order they are defined.

In this example, we're using the built-in middleware functions provided by Express.js. express.json() parses incoming requests with JSON payloads, and express.urlencoded() parses incoming requests with URL-encoded payloads.

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4. Serving Static Files

Express.js allows you to serve static files such as HTML, CSS, images, etc., using the express.static() middleware function.

In this example, we're serving static files from the public directory. Any files inside the public directory will be accessible from the browser.

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5. Templating Engines

Express.js seamlessly integrates with various templating engines such as EJS, Pug (formerly Jade), Handlebars, etc. Templating engines allow you to dynamically render HTML with data.

In this example, we've set EJS as the view engine. Now, you can create EJS templates and render them using the res.render() method.

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6. Error Handling

Express.js provides mechanisms to handle errors in your application. You can define error-handling middleware functions to handle errors and gracefully respond to the client.

In this example, we've defined a generic error handler that logs the error to the console and sends a generic error message to the client.

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Middleware Chaining

You can chain multiple middleware functions together using app.use() or app.METHOD(). This allows you to apply middleware to specific routes or globally to your application.

In this example, the authentication and authorization middleware functions will be applied only to routes that start with /api.

Congratulations! You've now learned the basics of Express.js and how to work with it. Express.js offers a vast array of features and extensions that can help you build robust web applications with ease.