Node.js - First Apppcation

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

Import required modules − We use the require directive to load Node.js modules.

Create server − A server which will psten to cpent s requests similar to Apache HTTP Server.

Read request and return response − The server created in an earper step will read the HTTP request made by the cpent which can be a browser or a console and return the response.

Creating Node.js Apppcation

Step 1 - Import Required Module

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

var http = require("http");

Step 2 - Create Server

We use the created http instance and call http.createServer() method to create a server instance and then we bind it at port 8081 using the psten method associated with the 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
 );
}).psten(8081);

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

The above code is enough to create an HTTP server which pstens, i.e., waits for a request over 8081 port on the 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
 );
}).psten(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 the Node.js Server

Open http://127.0.0.1:8081/ in any browser and observe the following result.