What is Node.js?

Node.js is a framework built upon the JavaScript Engine “V8“, which is currently the most used JavaScript Engine and built into Google Chrome.

Node.js was developed by the need of a resource efficient, performant, “nonblocking I/O” Framework to deliver fast and quick websites.

Here is an example of a very basic web-server written in Node.js

const http = require('http');

const hostname = '127.0.0.1';
const port = 3000;

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

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

Main requirement to run this code is the fact, that you need a Node.js version installed on your system (see https://nodejs.org)
The current LTS version is fine.

Now we can start the webserver with

node index.js

and can see the following output in the terminal

Server running at http://127.0.0.1:3000/

If we open up a browser with the given URL we see

Advantages of Node.js

• Based on JavaScript there is very little to no new syntax to lean if you know the basics of JavaScript.
• Node.js is event based (see HERE for more detials) and because of that very performant
• Modularity with the Node-Package-Manager (NPM)

Disadvantages of Node.js

• Backwards compatibility is somewhat a problem with upcoming Node.js version updates because the current development of the framework is so rapid.
• The fact that Node.js works on an event loop implies only 1 thread has to carry all the work which can be overwhelmed by lots of requests and/or server logic.
• Asynchron code notation can be tricky to understand and learn

Source: https://nodejs.org/de/about/