Handling HTTP Requests in Express.js

Express.js is a popular Node.js framework for building web applications. It provides a flexible and modular way to handle HTTP requests and responses. In this article, we will explore the basics of handling HTTP requests in Express.js.

Understanding HTTP Requests

HTTP (Hypertext Transfer Protocol) is a protocol used for transferring data over the web. It is a request-response protocol, where a client (usually a web browser) sends a request to a server, and the server responds with the requested data.

There are several types of HTTP requests, including:

• GET: Retrieves data from the server
• POST: Sends data to the server to create a new resource
• PUT: Updates an existing resource on the server
• DELETE: Deletes a resource from the server

Handling HTTP Requests in Express.js

In Express.js, you can handle HTTP requests using the following methods:

• app.get(): Handles GET requests
• app.post(): Handles POST requests
• app.put(): Handles PUT requests
• app.delete(): Handles DELETE requests

These methods take two arguments: the route path and a callback function. The callback function is executed when the request is received.

Example: Handling a GET Request

const express = require('express');
const app = express();

app.get('/', (req, res) => {
  res.send('Hello World!');
});

app.listen(3000, () => {
  console.log('Server started on port 3000');
});

In this example, we create an Express.js app and define a route for the root URL ('/'). When a GET request is received, the callback function is executed, and the string 'Hello World!' is sent back to the client.

Example: Handling a POST Request

const express = require('express');
const app = express();
const bodyParser = require('body-parser');

app.use(bodyParser.json());

app.post('/users', (req, res) => {
  const { name, email } = req.body;
  console.log(`Received data: ${name}, ${email}`);
  res.send('User created successfully!');
});

app.listen(3000, () => {
  console.log('Server started on port 3000');
});

In this example, we create an Express.js app and define a route for the '/users' URL. We use the body-parser middleware to parse the request body as JSON. When a POST request is received, the callback function is executed, and the data is extracted from the request body.

Request Object

The request object (req) is an instance of the HTTP request object. It provides information about the request, including:

• req.method: The HTTP method used (e.g., GET, POST, PUT, DELETE)
• req.url: The URL of the request
• req.headers: The HTTP headers of the request
• req.body: The request body (parsed as JSON or URL-encoded)

Response Object

The response object (res) is an instance of the HTTP response object. It provides methods for sending responses back to the client, including:

• res.send(): Sends a response with a string or buffer
• res.json(): Sends a response with a JSON object
• res.status(): Sets the HTTP status code of the response

Conclusion

In this article, we explored the basics of handling HTTP requests in Express.js. We learned how to define routes for different HTTP methods, extract data from the request body, and send responses back to the client. With this knowledge, you can build robust and scalable web applications using Express.js.

Frequently Asked Questions

Q: What is the difference between app.get() and app.post()?

A: app.get() handles GET requests, while app.post() handles POST requests. GET requests are used to retrieve data from the server, while POST requests are used to send data to the server to create a new resource.

Q: How do I extract data from the request body?

A: You can use the body-parser middleware to parse the request body as JSON or URL-encoded. Then, you can access the data using the req.body object.

Q: How do I send a response back to the client?

A: You can use the res.send() method to send a response with a string or buffer. You can also use the res.json() method to send a response with a JSON object.

Q: What is the purpose of the request object (req)?

A: The request object (req) provides information about the request, including the HTTP method, URL, headers, and body.

Q: What is the purpose of the response object (res)?

A: The response object (res) provides methods for sending responses back to the client, including res.send(), res.json(), and res.status().