Node.js – 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 −

• Import required modules − We use the require directive to load Node.js modules.
• Create server − A server which will listen to client's requests similar to Apache HTTP Server.
• 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 3000 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".

  var http = require("http");
  http.createServer(function (req, res){
  // Send the HTTP header
  // HTTP Status: 200 : OK
  // Content Type: text/plain
  res.writeHead(200, {'Content-Type': 'text/plain'});
  // Send the response body as "hello this is node tutorial"
  res.end("hello this is node tutorialn")
  }).listen(3000,console.log("sertver is listening at port no 3000"))

  The above code is enough to create an HTTP server which listens, i.e., waits for a request over 300 port on the local machine.

  Step 3 - Testing Request & Response

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

  var http = require("http");
  http.createServer(function (req, res){
  // Send the HTTP header
  // HTTP Status: 200 : OK
  // Content Type: text/plain
  res.writeHead(200, {'Content-Type': 'text/plain'});
  res.end("hello this is node tutorialn")
  }).listen(3000,console.log("Server running at http://127.0.0.1:3000/"))

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

  node app.js

  Verify the Output. Server has started.

  Server running at http://127.0.0.1:3000/

  Make a Request to the Node.js Server

  Open http://127.0.0.1:3000/ 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 3000.