What is Node.js?

Node.js (or just Node) is a lean, fast, cross-platform JavaScript runtime environment that is useful for both servers and desktop applications. Node is an asynchronous event driven JavaScript runtime built upon Chrome’s V8 JavaScript engine. It’s designed to build scalable network applications.

That being the raw definition, let me clarify. Node.js enables you to write server side JavaScript. You may now be wondering, how? As you know, JavaScript is a language which runs in a browser. The browser’s engine takes JavaScript code and compiles it into commands. The creator of Node.js took Chrome’s engine and built a runtime for it to work on a server. Don’t get confused with the word runtime. It’s an environment where the language can get interpreted. So what do we have now? A way to write JavaScript on the back end.

Regarding the definition, you might be wondering what the term asynchronous even means in the current context. JavaScript is single threaded, meaning there is only one thread of execution. So you don’t want events to interrupt the main thread of execution. This is what asynchronous means, handling events without interrupting the main thread. Node is based on this non-blocking execution, making it one of the fastest tools for building web applications today.

In the following “Hello World” example, many connections can be handled concurrently. Upon each connection the callback is fired, but if there is no work to be done Node will remain asleep.

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}/`);
});

Non-blocking I/O makes Node.js very fast, lightweight, scalable, and efficient in handling data-heavy and I/O-heavy workloads characteristic of several types of web applications. Node.js can be used efficiently in many kinds of applications, and we will present six most popular solutions, including IoT applications, applications built around microservice architecture, real-time chats, real-time collaboration tools, streaming apps, and Single Page Applications (SPAs).

To summarize, Node is a cross-platform JavaScript runtime environment for servers and applications. It is built on a single-threaded, non-blocking event loop, the Google Chrome V8 JavaScript engine, and a low-level I/O API. Various techniques, including the cluster module, allow Node.js apps to scale beyond a single CPU core. Beyond its core functionality, Node.js has inspired an ecosystem of half a million packages that are registered and versioned in the NPM repository and can be installed using the NPM command line or an alternative such as Yarn.

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