Node.js Web Server

13 Oct, 2021
What is Node.js ?Node.js is an open source server environment. Node.js uses JavaScript on the server. The task of a web server is to open a file on the server and return the content to the client.
Node.js has a built-in module called HTTP, which allows Node.js to transfer data over the Hyper Text Transfer Protocol (HTTP). The HTTP module can create an HTTP server that listens to server ports and gives a response back to the client.
Example:
// Import the Node.js http modulevar http = require('http');   // req is the request object which is// coming from the client side// res is the response object which is going// to client as response from the server  // Create a server objecthttp.createServer(function (req, res) {  // 200 is the status code which means// All OK and the second argument is// the object of response header.res.writeHead(200, {'Content-Type': 'text/html'});       // Write a response to the client    res.write('Congrats you have a created a web server');      // End the response    res.end();  }).listen(8081); // Server object listens on port 8081  console.log('Node.js web server at port 8081 is running..')
The function passed in the http.createServer() will be executed when the client goes to the url http://localhost:8081.
Steps to run the code:
Save the above code in a file with .js extension
Open the command prompt and goes to the folder where the file is there using cd command.
Run the command node file_name.js
Open the browser and go the url http://localhost:8081
When http://localhost:8081 is opened in browser.
The http.createServer() method includes request object that can be used to get information about the current HTTP request e.g. url, request header, and data.
The following example demonstrates handling HTTP request and response in Node.js.
// Import Node.js core module i.e httpvar http = require('http');   // Create web servervar server = http.createServer(function (req, res) {            // Check the URL of the current request    if (req.url == '/') {                   // Set response header        res.writeHead(200, { 'Content-Type': 'text/html' });                    // Set response content            res.write(          `<html><body style="text-align:center;">            <h1 style="color:green;">GeeksforGeeks Home Page</h1>            <p>A computer science portal</p>            </body></html>`);        res.end();//end the response           }    else if (req.url == "/webtech") {                   res.writeHead(200, { 'Content-Type': 'text/html' });        res.write(`          <html><body style="text-align:center;">            <h1 style="color:green;">Welcome to GeeksforGeeks</h1>            <a href="https://www.geeksforgeeks.org/web-technology/">              Read Web Technology content            </a>          </body></html>`);        res.end();//end the response           }    else if (req.url == "/DS") {                   res.writeHead(200, { 'Content-Type': 'text/html' });        res.write(`<html><body style="text-align:center;">          <h1 style="color:green;">GeeksforGeeks</h1>          <a href="https://www.geeksforgeeks.org/data-structures/">            Read Data Structures Content          </a>        </body></html>`);        res.end(); //end the response           }    else if (req.url == "/algo") {                 res.writeHead(200, { 'Content-Type': 'text/html' });      res.write(`<html><body style="text-align:center;">        <h1 style="color:green;">GeeksforGeeks</h1>        <a href="https://www.geeksforgeeks.org/fundamentals-of-algorithms/">          Read Algorithm analysis and Design Content        </a>      </body></html>`);      res.end(); //end the response       }    else        res.end('Invalid Request!'); //end the response   // Server object listens on port 8081}).listen(3000, ()=>console.log('Server running on port 3000'));
In the above example, req.url is used to check the url of the current request and based on that it sends the response.Command to Run code:
node index.js
Output:
URL: localhost:3000
URL: localhost:3000/webtech
URL: localhost:3000/DS
URL: localhost:3000/algo
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