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What does it mean to say nodeJS is built on the V8 engine?

I'm beginner to MEAN stack, while studying NodeJS, I'm came up with the following statement that's taking my mind
Node.js is a very powerful JavaScript-based framework/platform built
on Google Chrome's JavaScript V8 Engine.
but what exactly does it mean by
built on Google Chrome's JavaScript V8 Engine.
and if it's built on Chrome's JS V8 Engine, why does it works on Firefox as well?

MEAN stack, reorganized from back to front:
MongoDB: data persistence, stores data for later retrieval
Node.js: web application server, responds to requests from clients
Express: web application framework, reduces Node boilerplate
Angular.js: browser framework
So Node.js does not "work on Firefox" (it doesn't work on Google Chrome either): its a server-side technology. Think of it as a replacement for Python/Ruby/Java in that role. So it can/does respond to requests from all sorts of clients (like Google Chrome and Firefox).
What the "built on V8" means is that it uses the same JavaScript interpreter/just-in-time compiler as Google Chrome. But the similarities with chrome pretty much stop there: Node has no rendering engine/css parser/DOM but does have things you need in a server like an HTTP library and a filesystem API.
Also, and I mean no offence: we all started where you are, the fact that you are even asking the question (which again is not a bad thing!) means that building on a stack like MEAN is over your head. The documentation is going to assume that you know things you seem to not know. I strongly recommend furthering your understanding of JavaScript and Node through some tutorials and barebones test apps before trying to throw databases and frameworks into the mix.

In order for a programming language to be executed by a computer, it needs to be translated into a format the machine can understand (generally termed machine code). Javascript is no different. When your browser is presented with Javascript code on a website, something needs to compile or, in the case of Javascript, interpret the instructions into machine code.
V8 is the program that was developed by Google to do exactly that. When you use Chrome and it detects Javascript on a page, it passes it to V8 to run the compilation and then your computer executes the resulting code.
V8 was open sourced by Google. The creator of Node, Ryan Dahl, modified the source code so that V8 could be used outside of Chrome and inside an operating system like Linux or MacOS. That is what is meant by your first quote.
The important thing to note here is that you do not execute your Node programs in a browser but rather with the actual computer you are using. There's no correlation between V8 and Firefox, Safari, IE, etc. All of those browsers have their own Javascript interpreters.

Ok let's get through this:
Node.js is a very powerful JavaScript-based framework/platform built on
Google Chrome's JavaScript V8 Engine.
JavaScript is a programming language used in internet browsers. It was invented in 1995 by NetScape, I think, and has been submitted to a certification organization called ECMA in 1996.
ECMA has taken the original idea of JavaScript and made a standard called ECMAScript which each JavaScript implementation should follow. You see, JavaScript is not a language that just exists somewhere in the ether - each internet browser comes with it's own implementation of the language - this means that JavaScript usually only works in internet browsers such as Mozilla, Safari, Opera or Chrome for example. (Internet Explorer also comes with an implementation of ECMAScript but they call it JScript for licensing reasons I believe)
The implementation of JavaScript that comes with Google Chrome runs on the powerful V8 engine which is written in a language called C++. V8 interprets your JavaScript code and provides it all the variable types, manages memory etc. The great thing about V8 is that it is open-source and can be embedded in any other C++ program.
So the creators of Node had the idea of taking V8 and enhancing it by adding features that a server needs to serve websites - reading files, responding to requests, routing etc. This means that it is now possible to program the server-side implementation of a website using JavaScript thanks to the Node.js application that interprets your code and essentially translates it to C++ and later machine code further down the line. The important distinction is that Node.js DOES NOT run in your browser! It runs on a server much like when you code the back-end using PHP and apache.

V8 Engine is an interpreter for Javascript used in Google Chrome.
The statement that NodeJS is built on top of this engine means that it uses this interpreter for it's own thing, so it can also be used on the server, not just in the desktop environment (like in Google Chrome).
NodeJS is a separate application that you can communicate with over the internet, it's like Apache, Nginx or similar, but it's not used for one thing only (like the ones mentioned), but it's mostly used for making web-server like applications.

Node uses the same JS "engine" that runs chrome.
An engine in this case, is a piece of software that compiles, or "translates" your JS code into machine code; or the 0s and 1s your computer can understand.
This compilation is a complex process, and there are a few different approaches to solving it, for example google's v8 or mozilla's spidermonkey. Each of these support the entire JS standard (to a certain extent), i.e any JavaScript code can run on them.
When you run a node server, it runs on a machine that acts as a server. The code is not run on the user's machine at all; hence it doesn't matter which browser is used to view your content.
In the MEAN stack, it's angular code that runs on the user's computer. However, it is written in JavaScript, which can be run on any javascript engine.

Node.js is JavaScript on the server. For example, you can start a Node.js server on http://localhost:8000/, and you can access it with Chrome or Firefox.
Using Node.js (which uses V8), servers can be written in JavaScript rather than PHP or Ruby.

Actually NodeJS is cross platform server side framework. You might know as it is best suited for I/O bound and Data Streaming Applications, it uses Google Chrome's JavaScript V8 Engine for above mentioned purposes
So it's independent of browser and platform.

what is browser's native support according to selenium webdriver

While learning about selenium, I came to know that:
Selenium
Webdriver
makes direct calls to the
browser using each browser’s native support for
automation
I want to know, What is this native support? Is it "some HTML code", or "javascript code"?
Is there any good web link, where I can know that in what language or script, browsers are written in?

Your language-binded code (for example, Java) implements WebDriver Interface which communicates with different browser drivers via HTTP commands.
Those drivers communicate natively (not http / JS injections / OS wrapping) with the browser.
By the way, here's lay the main difference between Selenium 2 and Selenium 3. in Selenium 2 it was the Selenium project responsibility to provide the driver for each browser and in Selenium 3 all the major browser vendors ship their own WebDriver implementations and because they know their browsers the best, it's much more stable and robust.
About the native implementations. Each browser native implementation is different and tightly couple to the way browser works!
For example, Chrome driver. Communication is done via special Automation Proxy module:
And in Internet Explorer, it's done using Communication APIs:
Hope it helps.

For each and every browser some automation methods are defined by the vendors like for Chrome, Firefox they have some automation support built within them and the selenium uses the same for the test automation, in addition Selenium is the core of automation and that is why each and every browser has support for Selenium, so selenium has to just call that code and then the browser will work according to it.

I think following link gives some insight into the question.
http://taligarsiel.com/Projects/howbrowserswork1.htm
Browser engine is the component of a browser, which parses HTML, CSS and XML.

What is javascript runtime..? [duplicate]

This question already has answers here:
In JavaScript, what code executes at runtime and what code executes at parsetime?
(5 answers)
Closed 7 years ago.
As per the definition mentioned on https://nodejs.org/
Node.js is a platform built on Chrome's JavaScript run-time for easily building fast, scalable network applications. Node.js uses an event-driven, non-blocking I/O model that makes it lightweight and efficient, perfect for data-intensive real-time applications that run across distributed devices.
Can any one please help me understand what the JavaScript run-time exactly means?

Maybe it's referring to Google's V8 engine.
It is an engine for processing JavaScript in the browser and is used by Google Chrome.
It's open source.
And it's written in C++.
It works on several platforms including mobile and embedded devices.
For more information see: https://code.google.com/p/v8/
If you google for "chrome javascript runtime", you will get all these links to V8.

Chrome's javascript runtime is Google's V8 engine which was developed by Google to be used with Google Chrome.
It compiles the javascript code to native machine code instead of interpreting bytecode which gives a major performance boost to javascript (which is traditionally very slow compared to other high level languages).
Node.js contains libuv to handle asynchronous events. V8 provides the run-time for JavaScript.

It is a virtual machine which interprets and executes JavaScript mostly on browser. In fact Node.js is a javascript runtime based library.

The JavaScript Runtime (JsRT) APIs provide a way for desktop, Windows Store, and server-side applications running on the Windows operating system to add scripting capabilities to an app by using the standards-based Chakra JavaScript engine that is also utilized by Microsoft Edge and Internet Explorer. These APIs are available on Windows 10 and any version of the Windows operating system that has Internet Explorer version 11.0 installed on the machine.

Differences between Node environment and browser javascript environment

I've always been a bit annoyed that there are two major realms of javascript projects -- Node and "the browser" -- and while most browser JS can be easily run inside Node with a couple libraries for DOM stuff if needed, porting Node stuff to the browser is usually an afterthought.
This all seems like a lot of wasted energy on the part of developer communities, which could be alleviated by all JS developers just developing for the "least common denominator" (the browser) and using various shims to use features only available in Node or other JS environments besides the plain old browser.
This would not only cut out a lot ecosystem cruft and make development-in-the-browser more realistic, it also makes it commonplace to give the browser superpowers…Look for example at browserver, which sets up an http server inside the browser, but because the browser cannot actually accept http requests, uses websockets to talk to a proxy Node server that can.
So I want to ask, what are the real technical constraints of a web browser's javascript environment versus Node?
I thought Node was just "a javascript environment, plus http server and local filesystem, minus the DOM and the chrome". Are there technical reasons why developers could not potentially move to the approach I described above, developing for the browser JS environment (does this have an official name?) and using shims for Node?

Code that runs on the client usually have very different goals from the code that runs on the server. However when it makes sense to use some libarary's features in both environments there are a lot of them that are defined using a universal AMD form which makes them platform independent (e.g. Q).
The major difference between both environments is that one is subject to rigorous security policies and restrictions (browser) while the other isin't. The browser is also an untrustable environment for security-related operations such as enforcing security permissions.
I'll also add #jfriend00 comment in here since I believe it's also very relevant a exposes other differences:
The biggest practical difference is that you have to design a browser
application to work in an installed base of existing browsers
including older versions (lowest common denominator). When deploying a
node application, you get to select the ONE version of node that you
want to develop for and deploy with. This allows node developers to
use the latest greatest features in node which won't be available
across the general browser population for years. #jfriend00
Projects like browserver are interesting and I am all for experimental development, but are they truly useful in practice? Libraries should be designed for the environment in which they are truly useful. There are no benefits in making all libraries available in both environments. Not only that it will generally result in an increased code complexity, some features will sometimes not be shimmable resulting in an inconsistent API between platforms.

Here are some of the differences between these two environments:
Node.js has built-in libraries for HTTP and socket communication with which it can create a web server and thus be a replacement for other types of servers such as. Apache or Nginx
Node.js does not have browser APIs related to DOM, CSS, performance, document, as well as all APIs associated with the "window" object. Precisely because of the lack of a window object, the global object was renamed "global".
Node.js has full access to the system like any other source application. This means it can read and write directly to or from the file system, it can also have unlimited network access, and it can execute software...
Since the development of JavaScript is moving very fast, browsers often lag behind the implementation of new features of JavaScript, so you need to use an older version of JavaScript in the Browser, but this does not apply to Node.js, you can use it all modern ES6-7-8-9 JavaScript if your version of Node.js supports it.
Although within ES6 there is a syntax for working with modules (import/export syntax), it has only recently been added to node.js as an experimental option. Node.js mainly uses CommonJS syntax to work with modules.

Difference between JavaScript Extensions and NPAPI plugins with respect to performance

I have written a windowless NPAPI plugin which binds to a shared library for accessing my native resources. The plugin is loaded by a web Application running in Firefox browser.
Recently, I have seen in net, that using Java Script extensions, one can also make native code function calls.But these Java Script extensions are specific to browsers.
Can some one please tell me that if I use a Java Script extension instead of NPAPI plugin for calling my native code, will there be any performance improvement in terms of latency in making native library API calls?
Kindly note: My query is generic and not specifically for Firefox browser.

There is no generic answer to a question like this, the mechanisms implemented by different browsers have nothing in common.
Firefox: A native library can be called via js-ctypes. This mechanism should be more light-weight than the communication with an NPAPI plugin. Even more importantly, you don't have the overhead of inter-process communication (newer Firefox versions run plugins in separate processes).
Chrome: AFAIK the only way to access operating system functionality (such as writing files to a random location on disk) is via NPAPI, Chrome won't allow extensions to use system libraries. However, if you use a native library only to speed up execution and don't mind having this code run in a sandbox - the native client might work for you. Due to sandboxed execution it will probably be slower than an NPAPI plugin but it won't trigger huge scary warnings when your extension is installed.
Safari: From what I know, Safari doesn't let you use native libraries, not even via NPAPI plugins.
Internet Explorer: As of MSIE 9.0, Internet Explorer still doesn't have anything resembling JavaScript-based extensions.