Node.js is an open-source, cross-platform JavaScript run-time environment for executing JavaScript code server-side. Historically, JavaScript was used primarily for client-side scripting, in which scripts written in JavaScript are embedded in a webpage's HTML, to be run client-side by a JavaScript engine in the user's web browser. Node.js enables JavaScript to be used for server-side scripting, and runs scripts server-side to produce dynamic web page content before the page is sent to the user's web browser. Consequently, Node.js has become one of the foundational elements of the "JavaScript everywhere" paradigm, allowing web application development to unify around a single programming language, rather than rely on a different language for writing server side scripts.
Though .js is the conventional filename extension for JavaScript code, the name "Node.js" does not refer to a particular file in this context and is merely the name of the product. Node.js has an event-driven architecture capable of asynchronous I/O. These design choices aim to optimize throughput and scalability in Web applications with many input/output operations, as well as for real-time Web applications (e.g., real-time communication programs and browser games).
The Node.js distributed development project, governed by the Node.js Foundation, is facilitated by the Linux Foundation's Collaborative Projects program.
Corporate users of Node.js software include GoDaddy, Groupon, IBM, LinkedIn, Microsoft, Netflix, PayPal, Rakuten, SAP, Tuenti, Voxer, Walmart, Yahoo!, and Cisco Systems.
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History
Node.js was originally written by Ryan Dahl in 2009, about thirteen years after the introduction of the first server-side JavaScript environment, Netscape's LiveWire Pro Web. The initial release supported only Linux and Mac OS X. Its development and maintenance was led by Dahl and later sponsored by Joyent.
Dahl was inspired to create Node.js after seeing a file upload progress bar on Flickr. The browser did not know how much of the file had been uploaded and had to query the Web server. Dahl desired an easier way.
Dahl criticized the limited possibilities of the most popular web server in 2009, Apache HTTP Server, to handle a lot of concurrent connections (up to 10,000 and more) and the most common way of creating code (sequential programming), when code either blocked the entire process or implied multiple execution stacks in the case of simultaneous connections.
Dahl demonstrated the project at the inaugural European JSConf on November 8, 2009. Node.js combined Google's V8 JavaScript engine, an event loop and a low-level I/O API. The project received a standing ovation.
In January 2010, a package manager was introduced for the Node.js environment called npm. The package manager makes it easier for programmers to publish and share source code of Node.js libraries and is designed to simplify installation, updating and uninstallation of libraries.
In June 2011, Microsoft and Joyent implemented a native Windows version of Node.js. The first Node.js build supporting Windows was released in July 2011.
In January 2012, Dahl stepped aside, promoting coworker and npm creator Isaac Schlueter to manage the project. In January 2014, Schlueter announced that Timothy J. Fontaine would lead the project.
In December 2014, Fedor Indutny started io.js, a fork of Node.js. Due to the internal conflict over Joyent's governance, io.js was created as an open governance alternative with a separate technical committee. Unlike Node.js, the authors planned to keep io.js up-to-date with the latest releases of the Google V8 JavaScript engine.
In February 2015, the intent to form a neutral Node.js Foundation was announced. By June 2015, the Node.js and io.js communities voted to work together under the Node.js Foundation.
In September 2015, Node.js v0.12 and io.js v3.3 were merged back together into Node v4.0. This brought V8 ES6 features into Node.js, and a long-term support release cycle. As of 2016, the io.js website recommends that developers switch back to Node.js and that no further releases of io.js are planned due to the merger.
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Overview
Node.js allows the creation of Web servers and networking tools using JavaScript and a collection of "modules" that handle various core functionality. Modules are provided for file system I/O, networking (DNS, HTTP, TCP, TLS/SSL, or UDP), binary data (buffers), cryptography functions, data streams and other core functions. Node.js's modules use an API designed to reduce the complexity of writing server applications.
Node.js applications can run on Linux, macOS, Microsoft Windows, NonStop, and Unix servers. They can alternatively be written with CoffeeScript (a JavaScript alternative), Dart or Microsoft TypeScript (strongly typed forms of JavaScript), or any other language that can compile to JavaScript.
Node.js is primarily used to build network programs such as Web servers. The biggest difference between Node.js and PHP is that most functions in PHP block until completion (commands execute only after previous commands have completed), while functions in Node.js are designed to be non-blocking (commands execute in parallel, and use callbacks to signal completion or failure).
Platform architecture
Node.js brings event-driven programming to web servers, enabling development of fast web servers in JavaScript. Developers can create highly scalable servers without using threading, by using a simplified model of event-driven programming that uses callbacks to signal the completion of a task. Node.js was created because concurrency is difficult in many server-side programming languages, and often leads to poor performance. Node.js connects the ease of a scripting language (JavaScript) with the power of Unix network programming.
Node.js was built on the Google V8 JavaScript engine since it was open-sourced under the BSD license, extremely fast, and proficient with internet fundamentals like HTTP, DNS, TCP. Also, JavaScript was a well-known language, making Node.js immediately accessible to the entire web development community.
Industry support
People have built thousands of open-source libraries for Node.js - most of them hosted on the npm website. The Node.js developer community has two main mailing lists and the IRC channel #node.js on freenode. There is an annual Node.js developer conference, called NodeConf.
The open-source community has developed server frameworks to accelerate the development of applications. Such frameworks include Connect, Express.js, Socket.IO, Koa.js, Hapi.js, Sails.js, Meteor, Derby, and many others.
Modern desktop IDEs provide editing and debugging features specifically for Node.js applications. Such IDEs include Atom, Brackets, JetBrains WebStorm, Microsoft Visual Studio (with Node.js Tools for Visual Studio, or TypeScript with Node definitions), NetBeans, Nodeclipse Enide Studio (Eclipse-based) and Visual Studio Code. Certain online web-based IDEs also support Node.js, such as Codeanywhere, Codenvy, Cloud9 IDE, Koding and the visual flow editor in Node-RED.
Releases
New major releases of Node.js are cut from the Github master branch every six months. Even-numbered versions are cut in April and odd-numbered versions are cut in October. When a new odd version is released, the previous even version transitions to Long Term Support (LTS), which gives that version 18 months of active support from the date it is designated LTS. After these 18 months expire, an LTS release will receive an additional 12 months of maintenance support. An active version will receive non-breaking backports of changes a few weeks after they land in the current release. A maintenance release will only receive critical fixes and documentation updates.
The strategy and policy of LTS releases are managed by the LTS Working Group in collaboration with the Technical Steering Committee of the Node.js Foundation.
Technical details
Node.js is a Javascript runtime environment that processes incoming requests in a loop, called the event loop.
Threading
Node.js operates on a single thread, using non-blocking I/O calls, allowing it to support tens of thousands of concurrent connections without incurring the cost of thread context switching. The design of sharing a single thread between all the requests that uses the observer pattern is intended for building highly concurrent applications, where any function performing I/O must use a callback. In order to accommodate the single-threaded event loop, Node.js utilizes the libuv library that in turn uses a fixed-sized thread pool that is responsible for some of the non-blocking asynchronous I/O operations.
A downside of this single-threaded approach is that Node.js doesn't allow vertical scaling by increasing the number of CPU cores of the machine it is running on without using an additional module, such as cluster, StrongLoop Process Manager or pm2. However, developers can increase the default number of threads in the libuv thread pool; these threads are likely to be distributed across multiple cores by the server operating system.
Execution of parallel tasks in Node.js is handled by a thread pool. The main thread call functions post tasks to the shared task queue that threads in the thread pool pull and execute. Inherently non-blocking system functions like networking translates to kernel-side non-blocking sockets, while inherently blocking system functions like file I/O run in a blocking way on its own thread. When a thread in the thread pool completes a task, it informs the main thread of this that in turn wakes up and execute the registered callback. Since callbacks are handled in serial on the main thread, long lasting computations and other CPU-bound tasks will freeze the entire event-loop until completion.
V8
V8 is the JavaScript execution engine built for Google Chrome and open-sourced by Google in 2008. Written in C++, V8 compiles JavaScript source code to native machine code instead of interpreting it in real time.
Node.js uses libuv to handle asynchronous events. Libuv is an abstraction layer for network and file system functionality on both Windows and POSIX-based systems like Linux, macOS, OSS on NonStop and Unix.
The core functionality of Node.js resides in a JavaScript library. The Node.js bindings, written in C++, connect these technologies to each other and to the operating system.
Package management
npm is the pre-installed package manager for the Node.js server platform. It is used to install Node.js programs from the npm registry, organizing the installation and management of third-party Node.js programs. npm is not to be confused with the CommonJS require() statement. It is not used to load code; instead, it is used to install code and manage code dependencies from the command line. The packages found in the npm registry can range from simple helper libraries like Lodash to task runners like Grunt.
Unified API
Node.js can be combined with a browser, a database supporting JSON data (such as Postgres, MongoDB or CouchDB) and JSON for a unified JavaScript development stack. With the adaptation of what were essentially server-side development patterns like MVC, MVP, MVVM, etc., Node.js allows the reuse of the same model and service interface between client-side and server-side.
Event loop
Node.js registers itself with the operating system in order to be notified when a connection is made, and the operating system will issue a callback. Within the Node.js runtime, each connection is a small heap allocation. Traditionally, relatively heavyweight OS processes or threads handled each connection. Node.js uses an event loop for scalability, instead of processes or threads. In contrast to other event-driven servers, Node.js's event loop does not need to be called explicitly. Instead callbacks are defined, and the server automatically enters the event loop at the end of the callback definition. Node.js exits the event loop when there are no further callbacks to be performed.
Project governance
In 2015, various branches of the greater Node.js community began working under the vendor-neutral Node.js Foundation. The stated purpose of the organization "is to enable widespread adoption and help accelerate development of Node.js and other related modules through an open governance model that encourages participation, technical contribution, and a framework for long-term stewardship by an ecosystem invested in Node.js' success."
The Node.js Foundation Technical Steering Committee (TSC) is the technical governing body of the Node.js Foundation. The TSC is responsible for the core Node.js repo as well as dependent and adjacent projects. Generally the TSC delegates administration of these projects to working groups or committees. The LTS group which manages long term supported releases is one such group. Other current groups include: Website, Streams, Build, Diagnostics, i18n, Evangelism, Docker, Addon API, Benchmarking, Post-mortem, Intl, Documentation, and Testing.
Alternatives
Similar open source event-driven server frameworks for other platforms include:
- EventMachine for Ruby
- libuv for C
- Perl Object Environment for Perlfor Perl
- reactPHP (libev, ExtEvent or libevent) or amphp (libuv) for PHP
- Twisted for Python
- Vert.x for Java, JavaScript, Groovy, Ruby, Python, Scala, Clojure and Ceylon
Node.js may utilize code written in other programming languages using:
- Edge.js allows Microsoft .NET applications to run Node.js scripts in-process, and allows Node.js servers to utilize .NET compiled code via async callbacks.
- Luvit implements the Node.js APIs for the language Lua
- Node-julia allows using Julia with Node.js/io.js
- The COBOL bridge for Node.js allows using COBOL with Node.js
Source of the article : Wikipedia
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