Nodejs

Node.js is an open-source, cross-platform JavaScript run-time environment that executes JavaScript code outside of a browser. JavaScript is used primarily for client-side scripting, in which scripts written in JavaScript are embedded in a webpage's HTML and run client-side by a JavaScript engine in the user's web browser. Node.js lets developers use JavaScript to write command line tools and for server-side scripting-running scripts server-side to produce dynamic web page contentbeforethe page is sent to the user's web browser. Consequently, Node.js represents a "JavaScript everywhere" paradigm, unifying web application development around a single programming language, rather than different languages for server side and client side scripts.

Both your browser JavaScript and Node.js run on the V8 JavaScript runtime engine. This engine takes your JavaScript code and converts it into a faster machine code. Machine code is low-level code which the computer can run without needing to first interpret it.

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

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

Node.js package ecosystem, npm, is the largest ecosystem of open source libraries in the world.

Go for stateless as soon as possible. It's better to go for stateless right from the very beginning. If you're on NodeJS and PM2, you have to keep your code stateless if you want PM2 to multiply your runtime for load-balancing.

Not for CPU-intensive tasks

Javascript V8 Engine

Isolate

An isolate is a concept of an instance in V8. In Blink, isolates and threads are in 1:1 relationship. One isolate is associated with the main thread. One isolate is associated with one worker thread. An exception is a compositor worker where one isolate is shared by multiple compositor workers.

PM2

Advanced, production process manager for Node.js

PM2 is daemon process manager that will help you manage and keep your application online.

http://pm2.keymetrics.io

Difference between Node.js and PHP

PHP is powered by Zend engine whereas Node.js is powered by Google's V8 JavaScript engine.
PHP is synchronous while Node.js is asynchronous.
PHP is slower while Node.js is quicker.
PHP has a ready to install feature to use it on the server side whereas Node.js is a runtime environment for JavaScript on the server side.

NPM

NPM is the default package manager for JavaScript development. It helps you find and install packages (programs) that you can use in your programs.

You can add npm to a project simply by using the "npm init" command. When you run this command it creates a "package.json" file in the current directory. This is the file where your dependencies are listed, and npm views it as the ID card of the project.

package.json vs package-lock.json

package.json	package.lock.json
It contains basic information about the project.	It describes the exact tree that was generated to allow subsequent installs to have the identical tree.
It is mandatory for every project.	It is automatically generated for those operations where npm modifies either node_modules tree or package.json.
It records important metadata about the project.	It allows future devs to install the same dependencies in the project.
It contains information such as name, description, author, script, and dependencies.	It contains the name, dependencies, and locked version of the project.

Internals

How NodeJS keep I/O non-blocking

Socket I/O

These are your sockets listeners, readers or writes, your fetch, your axis, HTTP, TCP or UDP server. Any socket I/O is done on the main thread but only when socket is ready. Main thread is never block waiting.

File I/O

Read and writes to files on disk are blocking in most os, so node can't perform those on the main thread. So it spins up a worker thread to do the file read or write. Main thread remains unblocked while the thread is blocked.

DNS

Subtle dns queries are done all the time to resolve domains through the blocking lookup function, same as file io, Node spins up a thread and let it be block, keeping the main thread unblocked.