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.