Node.js - First Application

Before creating actual "Hello, World!" application using Node.js, let us see the parts of a Node.js application. A Node.js application consists of following three important parts −

• Import required modules − We use require directive to load a Node.js module.
• Create server − A server which will listen to client's request similar to Apache HTTP Server.
• Read request and return response − server created in earlier step will read HTTP request made by client which can be a browser or console and return the response.

Creating Node.js Application

Step 1 - Import required module

We use require directive to load http module and store returned HTTP instance into http variable as follows −

var http = require("http");

Step 2: Create Server

At next step we use created http instance and call http.createServer()method to create server instance and then we bind it at port 8081 using listenmethod associated with server instance. Pass it a function with parameters request and response. Write the sample implementation to always return "Hello World".

http.createServer(function (request, response) {

   // Send the HTTP header 
   // HTTP Status: 200 : OK
   // Content Type: text/plain
   response.writeHead(200, {'Content-Type': 'text/plain'});
   
   // Send the response body as "Hello World"
   response.end('Hello World\n');
}).listen(8081);

// Console will print the message
console.log('Server running at http://127.0.0.1:8081/');

Above code is enough to create an HTTP server which listens ie. wait for a request over 8081 port on local machine.

Step 3: Testing Request & Response

Let's put step 1 and 2 together in a file called main.js and start our HTTP server as shown below −

var http = require("http");

http.createServer(function (request, response) {

   // Send the HTTP header 
   // HTTP Status: 200 : OK
   // Content Type: text/plain
   response.writeHead(200, {'Content-Type': 'text/plain'});
   
   // Send the response body as "Hello World"
   response.end('Hello World\n');
}).listen(8081);

// Console will print the message
console.log('Server running at http://127.0.0.1:8081/');

Now execute the main.js to start the server as follows −

$ node main.js

Verify the Output. Server has started

Server running at http://127.0.0.1:8081/

Make a request to Node.js server

Open http://127.0.0.1:8081/ in any browser and see the below result.

Congratulations, you have your first HTTP server up and running which is responding all the HTTP requests at port 8081.