Section 17: NodeJS Introduction: Getting Started With Writing Server-side Code

The goals

💪🏻What Exactly Is NodeJS & How Does It Work?

✌🏻Installing & Running NodeJS

👍🏻Writing Our First NodeJS-driven Website

 

What is NodeJS?

A JavaScript Runtime

A tool for executing JavaScript code (outside of the browser)

Can be installed on ANY computer and hence be used to write and execute server-side JavaScript code

 

 

Working with the "Command Line"

The "Command Line" is a text-based interface that allows you to execute commands on your machine

It's a default tool pre-installed on every operating system

 

macOS: Terminal

Windows: Command Prompt

Linux: Bash

 

 

Using Status Codes

Web servers communicate the status of a request & response via standardized status codes

 

200

Success! Request parsed successfully, a response could be generated + sent without any problems

 

404

Client-side error! The requested resource / URL was not found. Hence the expected response could not be generated

 

401

Client-side error! The requesting client (user) is not authorized to access the requested resource / URL (e.g. because not logged in)

 

500

Server-side error! The request was valid but something went wrong on the server, hence the expected response could not be generated

 

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 −

const 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.

 

 

Sources

https://nodejs.org/en/download/

Download | Node.js

https://www.tutorialspoint.com/nodejs/nodejs_first_application.htm

Node.js - First Application