Node.js HTTP Request & Response

1. Introduction to HTTP in Node.js

Node.js uses the `http` module to create HTTP servers and handle client requests. This allows Node.js to serve web pages and API responses.

2. Creating a Simple HTTP Server

First, let's create a basic HTTP server that listens for incoming requests and sends back a response:

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const http = require('http');

http.createServer((req, res) => {
  res.writeHead(200, {'Content-Type': 'text/plain'});
  res.end('Hello, Node.js!');
}).listen(8080, () => {
  console.log('Server running at http://localhost:8080/');
});

This code creates a server that listens on port 8080. When accessed, it sends a plain-text response: "Hello, Node.js!"

3. Handling HTTP Requests

When a client makes a request, Node.js can inspect the request details, such as the URL, method, and headers. Here's how you can handle incoming requests:

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const http = require('http');

http.createServer((req, res) => {
  console.log('Request received');
  console.log('Method:', req.method);
  console.log('URL:', req.url);
  res.writeHead(200, {'Content-Type': 'text/plain'});
  res.end('Request details logged');
}).listen(8080, () => {
  console.log('Server running at http://localhost:8080/');
});

This example logs the request method and URL to the console whenever the server receives a request.

4. Sending HTTP Responses

Node.js provides the `res` object to send responses to clients. You can set the response status code and content type, and send data back to the client:

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const http = require('http');

http.createServer((req, res) => {
  res.writeHead(200, {'Content-Type': 'application/json'});
  const responseObj = { message: 'Hello, JSON!' };
  res.end(JSON.stringify(responseObj));
}).listen(8080, () => {
  console.log('Server running at http://localhost:8080/');
});

This sends a JSON response with a message "Hello, JSON!" when the client accesses the server.

5. Handling Query Parameters

HTTP requests can include query parameters in the URL. Here's how to parse and handle them:

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const http = require('http');
const url = require('url');

http.createServer((req, res) => {
  const query = url.parse(req.url, true).query;
  console.log('Query Parameters:', query);
  res.writeHead(200, {'Content-Type': 'text/plain'});
  res.end('Query parameters received');
}).listen(8080, () => {
  console.log('Server running at http://localhost:8080/');
});

This example uses the `url` module to parse query parameters from the URL and log them to the console.

6. Conclusion

Handling HTTP requests and responses in Node.js is fundamental for building web applications and APIs. With the built-in `http` module, you can create servers, read request details, and send custom responses. This flexibility is key to building dynamic and interactive web services.