What is node?

Node.js is a JavaScript runtime built on Chrome’s V8 JavaScript engine.

Node.js has a standard library for IO, networking and other common back-end tasks.

Its community provides a vast set of libraries easily installed and managed with NPM (Node Package Manager)

What is node?

Node.js uses an event-driven, non-blocking I/O model that makes it lightweight and efficient.

Node.js, as JS itself, is a single-threaded (Web Workers APIs are another story).

What is node?

Node.js is created by Ryan Dahl (leaves the project at 2012)

Install

Install from: nodejs official site

Manage multiple active node.js versions:

Node Version Manager (nvm)

nvm-windows

Update

			npm install npm@latest -g
		

Check installed versions

  		$ node --version
  		# node -v
  		# you should see the installed node version
  	

Node and EcmaScript Support

The new features from the JavaScript ECMA-262 specification are brought to Node.js developers in a timely manner

Overview over supported ECMAScript features in various versions of Node.js is given in node.green site.

References

Guides section @nodejs - docs

Node.js API docs

Blocking vs. Non-blocking

Reference: Visualization of the flow of work in Node.js

NodeJS Event Loop - Diagram

NodeJS Event Loop Overview

NodeJS is a Single Thread application. But it is built on top of a platform written in C++, which uses multi-thread to carry out tasks at the same time.

Each event (like user request) is placed into an Event Queue (organized as FIFO: First In First Out).

The Event Loop is an endless loop, which passes the requests to the C++ based Thread Pool and each request is registered a Callback function

When the request is finished handling, the corresponding Callback function will be executed.

Blocking vs Non-blocking IO - example

			const fs = require('fs');

			let fileName = './someData.txt';

			function blockingRead(fileName) {
				const data = fs.readFileSync(fileName, 'utf8');
				// blocks here until file is read

				console.log(`Sync data read:`);
				console.log(data);
			}

			function nonBlocking(fileName) {
				fs.readFile(fileName,'utf8', (err, data) => {
					if (err) {
						throw err;
					}else{
						console.log(`Async data read:`);
						console.log(data);
					}
				});

				// the callback  will be executed when data are readed.
			}

			console.log(`~~~ 1 ~~~ `);
			blockingRead(fileName);
			console.log(`~~~ 2 ~~~ `);

			console.log(`~~~ 3 ~~~ `);
			nonBlocking(fileName);
			console.log(`~~~ 4 ~~~ `);
		

Creating simple server

			const http = require('http');

			const hostname = '127.0.0.1';
			const port = process.env.PORT || 8080;

			const server = http.createServer((req, res) => {
				res.statusCode = 200
				res.setHeader('Content-Type', 'text/plain')
				res.end('Hello from My Server!\n')
			});

			server.listen(port, hostname, () => {
				console.log(`Nodejs server is running at http://${hostname}:${port}/`)
			});
		

Overview

npm is an open source package manager for JavaScript code.

Helps the developers to share and re-use packages.

It's the world’s largest software registry (modulecounts.com)

What is NPM?

NPM allows you to install external node packages (utility functions, libraries or whole frameworks) from the command line. They are the dependencies of your application.

You can install these packages either to your global node package folder or to your local project folder.

Global node packages are accessible from everywhere in the terminal and you have to install them only once to your global directory

Local node packages are accessible only from your project folder

What is NPM - official video

Install/Update

			# you may need sudo if you've installed node globally
			npm install npm@latest -g
		

initialize a npm project

Before starting your project, which will use node modules, you have to initialize the project, and write the package.json file

Only when you have that file, you can install new local packages via npm

			#initialize a npm project (-y == defaults for package.json)
			npm init -y
		

share a npm project

the package.json enables you to share your project with other developers without sharing all the node packages (the dependencies).

Someone who will use your project can simply install all packages by using npm install on the command line.

npm install script takes all the dependencies listed in the package.json file and installs them in the node_modules folder

package installation

			# Install package locally
			npm install <package>

			# Install package globally
			npm install -g <package>
		

The installed package will automatically appear in a folder called node_modules and will be listed in the package.json file next to your other dependencies.

Pros

Simplicity (just bindings to c libraries and V8)

Extremely fast - can handle hundreds of requests on a single thread.

if they are not CPU intensive

NodeJs is a perfect candidate for real time communication over internet. Combine it with Socket.IO and you will get a good scalable web socket server

Huge ecosystem and vibrant community

Cons

Node Js handles multiple requests using one single thread. If a problem occurs whole node js instance will crash along with any global data that was stored

when NodeJs gets a CPU intensive request, all the other requests get blocked till this CPU intensive request stops for an I/O

Deno

deno - A secure TypeScript runtime built on V8 (From the creator of node.js)