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Nodejs - First Application


Before creating an actual "Hello, World!" application using Node.js, let us see the components of a Node.js application. A Node.js application consists of the following three important components:
  1. Import required modules: We use the require directive to load Node.js modules.
  2. Create server: A server which will listen to client's requests similar to Apache HTTP Server.
  3. Read request and return response: The server created in an earlier step will read the HTTP request made by the client which can be a browser or a console and return the response.
Creating Node.js Application

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 listen 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\n');
}).listen(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 listens, 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\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 the Node.js Server

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

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