Handling Requests and Responses

Handling Requests and Responses

In this section, we will delve deeper into how Express handles incoming requests and outgoing responses. Understanding these concepts will enable you to build more interactive and dynamic web applications.

Working with Request and Response Objects

Express provides two important objects for handling HTTP requests and responses: req (request) and res (response).

1. Request Object (req)

   • Contains information about the HTTP request.
   • Properties include req.query, req.params, req.body, req.headers, and more.

2. Response Object (res)

   • Used to send a response back to the client.
   • Methods include res.send(), res.json(), res.status(), res.redirect(), and more.

Example: Basic request and response handling:

	// Importing the Express module
	const express = require('express');
	const app = express();
	const port = 3000;
	
	// Handling GET request at the root URL
	app.get('/', (req, res) => {
	  res.send('Hello, World!'); // Sending a plain text response
	});
	
	// Handling GET request at the '/json' URL
	app.get('/json', (req, res) => {
	  res.json({ message: 'Hello, World!' }); // Sending a JSON response
	});
	
	app.listen(port, () => {
	  console.log(`Server running at http://localhost:${port}/`);
	});

Parsing Request Bodies

To handle incoming data in the body of a POST request, you need middleware to parse the request body. Express provides built-in middleware for this purpose.

1. Using express.json() Middleware

   javascript Copy

   	// Importing the Express module
   	const express = require('express');
   	const app = express();
   	const port = 3000;
   	
   	// Middleware to parse JSON request bodies
   	app.use(express.json());
   	
   	// Handling POST request at the '/submit' URL
   	app.post('/submit', (req, res) => {
   	  const { name, age } = req.body; // Extracting data from the request body
   	  res.send(`Name: ${name}, Age: ${age}`);
   	});
   	
   	app.listen(port, () => {
   	  console.log(`Server running at http://localhost:${port}/`);
   	});

2. Using express.urlencoded() Middleware

   javascript Copy

   	// Importing the Express module
   	const express = require('express');
   	const app = express();
   	const port = 3000;
   	
   	// Middleware to parse URL-encoded request bodies
   	app.use(express.urlencoded({ extended: true }));
   	
   	// Handling POST request at the '/submit' URL
   	app.post('/submit', (req, res) => {
   	  const { name, age } = req.body; // Extracting data from the request body
   	  res.send(`Name: ${name}, Age: ${age}`);
   	});
   	
   	app.listen(port, () => {
   	  console.log(`Server running at http://localhost:${port}/`);
   	});

Handling Query Parameters and URL Parameters

1. Query Parameters: Accessed via req.query.

   javascript Copy

   	// Handling GET request with query parameters
   	app.get('/search', (req, res) => {
   	  const { term, page } = req.query; // Extracting query parameters
   	  res.send(`Search Term: ${term}, Page: ${page}`);
   	});

2. URL Parameters: Defined in the route path and accessed via req.params.

   javascript Copy

   	// Handling GET request with URL parameters
   	app.get('/user/:id', (req, res) => {
   	  const { id } = req.params; // Extracting URL parameter
   	  res.send(`User ID: ${id}`);
   	});

Sending Different Types of Responses

Express allows you to send various types of responses, such as plain text, JSON, and HTML.

1. Plain Text Response

   javascript Copy

   	// Handling GET request and sending a plain text response
   	app.get('/text', (req, res) => {
   	  res.send('This is a plain text response.');
   	});

2. JSON Response

   javascript Copy

   	// Handling GET request and sending a JSON response
   	app.get('/data', (req, res) => {
   	  res.json({ message: 'This is a JSON response.' });
   	});

3. HTML Response

   javascript Copy

   	// Handling GET request and sending an HTML response
   	app.get('/html', (req, res) => {
   	  res.send('<h1>This is an HTML response.</h1>');
   	});

Summary

In this section, we explored how to handle requests and responses in Express. You learned about the req and res objects, parsing request bodies, handling query and URL parameters, and sending different types of responses.