HTTP Modules

Let's explore how Node.js utilizes the built-in HTTP module to transfer data over the Hyper Text Transfer Protocol (HTTP).

The Built-in HTTP Module

Node.js provides a built-in module called HTTP, which allows you to create HTTP servers and handle HTTP requests and responses. To include the HTTP module, use the require() method:

var http = require('http');

Node.js as a Web Server

With the HTTP module, Node.js can act as a web server by creating an HTTP server that listens to server ports and responds to client requests. Use the createServer() method to create an HTTP server:

var http = require('http');

// Create a server object:
http.createServer(function (req, res) {
  res.write('Hello World!'); // Write a response to the client
  res.end(); // End the response
}).listen(8080); // The server object listens on port 8080

The function passed into the http.createServer() method will be executed when someone tries to access the computer on port 8080.

Add an HTTP Header

To display the response from the HTTP server as HTML, include an HTTP header with the correct content type:

var http = require('http');

http.createServer(function (req, res) {
  res.writeHead(200, {'Content-Type': 'text/html'});
  res.write('Hello World!');
  res.end();
}).listen(8080);

The first argument of the res.writeHead() method is the status code, where 200 means that all is OK, and the second argument is an object containing the response headers.

Read the Query String

The req argument of the function passed into http.createServer() represents the request from the client as an object (http.IncomingMessage object). It has a property called "url" which holds the part of the URL that comes after the domain name:

var http = require('http');

http.createServer(function (req, res) {
  res.writeHead(200, {'Content-Type': 'text/html'});
  res.write(req.url);
  res.end();
}).listen(8080);

Split the Query String

You can easily split the query string into readable parts using the built-in URL module:

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

http.createServer(function (req, res) {
  res.writeHead(200, {'Content-Type': 'text/html'});
  var q = url.parse(req.url, true).query;
  var txt = q.year + " " + q.month;
  res.end(txt);
}).listen(8080);