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.1 Understanding the role of Express.js
Express.js, commonly known as Express, is a
web application
framework for Node.js. It is designed to simplify the process of
building web applications and APIs by providing a robust set of
features and tools. Express.js is built on top of Node.js, which is a
server-side JavaScript runtime environment. It serves as a foundation
for
creating web servers and handling HTTP requests and responses
effectively.
The Role of Express.js
Express.js plays a important role in web development by acting as an
intermediary between the server and client. Its primary functions
include:
1. Routing
Express allows you to define routes for different URLs and HTTP
methods. This enables you to specify how your application should
respond to various requests. For example, you can create routes for
handling user authentication, retrieving data from a database, or
serving static files like HTML, CSS, and JavaScript.
2. Middleware
Middleware functions are a core concept in Express. They are used to
perform tasks such as request parsing, authentication, logging, and
error handling. Middleware functions can be added to the request
response cycle, providing a way to modularize and customize the
behavior of your application.
3. Templating
Express supports various templating engines like Pug, EJS, and
Handlebars. These engines allow you to generate dynamic HTML
pages by injecting data into templates. This is essential for rendering
web pages with dynamic content, such as user profiles or product
listings.
4. Static File Serving
Express simplifies the process of serving static files like images,
stylesheets, and client-side JavaScript. You can define a directory
where these files reside, and Express will automatically handle
requests for them.
5. Middleware and Third-Party Packages
Express can be extended with a wide range of middleware and thirdparty packages available in the Node.js ecosystem. This extensibility
allows you to add features like authentication with Passport.js,
session management, and data validation with ease.
6. RESTful APIs
Express is an excellent choice for building RESTful APIs. It provides a
clean and organized way to define API endpoints, handle request
payloads, and send JSON responses, making it a popular framework
for developing server-side components of web and mobile
applications.
7. WebSocket Support
While primarily an HTTP server framework, Express can be integrated
with WebSocket libraries like Socket.io to enable real-time
communication between clients and servers.
1.2 Installation and Setup of Express.js
Before you can start using Express.js, you need to install it and set up
a basic project structure. Follow these steps to get started:
Step 1: Install Node.js
Ensure that you have Node.js installed on your system. You can
download the latest version from the official Node.js website
(https://nodejs.org/).
Step 2: Create a New Directory for Your Project
Create a new directory where you want to work on your Express.js
project. Open your terminal or command prompt and navigate to
this directory.
mkdir my-express-app
cd my-express-app
Step 3: Initialize a Node.js Project
Run the following command to initialize a new Node.js project. This
will create a `package.json` file, which will store information about
your project and its dependencies.
npm init -y
Step 4: Install Express.js
To install Express.js, use npm (Node Package Manager) within your
project directory:
npm install express
This command will download and install Express.js along with its
dependencies into the “node_modules” directory of your project.
Step 5: Create an Express Application
Now that you have Express.js installed, you can create a basic
Express application. Create a new JavaScript file (e.g., “app.js” or
“index.js”) in your project directory.
- javascript
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 the code above:
We import the Express.js module and create an instance of the
Express application.
We define a route that responds to HTTP GET requests at the
root URL ("/") with the message "Hello, Express!".
We start the server and listen on port 3000.
Step 6: Run Your Express Application
To run your Express application, execute the following command in
your project directory:
node app.js
Your Express application will start, and you should see the message
"Server is running on port 3000" in the console. You can then access
your application by opening a web browser and navigating to
“http://localhost:3000”.
Congratulations! You've successfully installed and set up a basic
Express.js application.
1.3 Creating a Basic Express Application
In the code snippet provided in the previous section 1.2 (Create an
Express Applications), we created a basic Express application that
responds with "Hello, Express!" when accessed at the root URL. Let's
break down the key components of this application:
Importing Express
We start by importing the Express.js module:
- javascript
const express = require('express');
This line allows us to use the functionalities provided by Express
throughout our application.
Creating an Express Application
Next, we create an instance of the Express application:
- javascript
const app = express();
This “app” object represents our web application and provides
methods to define routes, use middleware, and start the server.
Defining a Route
In the code snippet, we define a route using the “app.get()” method:
- javascript
app.get('/', (req, res) => {
res.send('Hello, Express!');
});
Here's what happens in this code:
“app.get('/')” specifies that we are defining a route for HTTP
GET requests to the root URL ("/").
The second argument is a callback function that takes two
parameters, “req” and “res”. “req” represents the HTTP
request, and “res” represents the HTTP response.
Inside the callback function, we use “res.send()” to send the
response "Hello, Express!" back to the client.
Starting the Server
Finally, we start the server and listen on a specified port (in this case,
port 3000):
- javascript
app.listen(port, () => {
console.log(`Server is running on port ${port}`);
});
The “app.listen()” method starts the server and listens on the
specified port. When the server starts successfully, the callback
function is executed, and a message is logged to the console.
You can customize this basic Express application by defining more
routes, adding middleware, and integrating it with databases or
other third-party packages as needed
Launch your Graphy