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:

1. Import required modules: We use require directive to load a Node.js module.
2. Create server: A server which will listen to client's request similar to Apache HTTP Server.
3. 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 listen method 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 reuest over 8081 port on local machine.

   Step 3: Testing Request & Response

   Let's put step 1 and 2 together in a file called MyFirstNode.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 MyFirstNode.js

   Verify the Output. Server has started 

   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.