Node.js

Overview

Node.js allows the creation of web servers and networking tools using JavaScript and a collection of "modules" that handle various core functionalities. 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.

Since version 22.6.0, Node.js natively supports both JavaScript and TypeScript, allowing TypeScript files to be executed without a separate compilation step. The TypeScript support was contributed by Node.js TSC member Marco Ippolito. In addition, many compile-to-JS languages are available, allowing Node.js applications to also be written in CoffeeScript, Dart, ClojureScript, and others.

Node.js is primarily used to build network programs such as web servers. The most significant difference between Node.js and PHP is that most functions in PHP block until completion (commands execute only after previous commands finish), while Node.js functions are non-blocking (commands execute concurrently and use callbacks to signal completion or failure).

Node.js is officially supported by Linux, macOS and Microsoft Windows 8.1 and Server 2012 (and later), with Tier 2 support for SmartOS and IBM AIX and experimental support for FreeBSD. OpenBSD also works, and LTS versions are available for IBM i (AS/400). The source code may also be built on similar operating systems that are not officially supported, such as NonStop OS and Unix servers.

Platform architecture

Node.js enables development of fast web servers in JavaScript using event-driven programming. Developers can create scalable servers without using threading by using a simplified model that uses callbacks to signal the completion of a task. Node.js connects the ease of a scripting language (JavaScript) with the power of Unix network programming.

Node.js was built on top of Google's V8 JavaScript engine, which Google had open-sourced under a BSD 3-Clause license in September 2008 alongside the initial release of Google Chrome. Dahl selected V8 for its high performance and its just-in-time compilation of JavaScript to native machine code, and paired it with a libuv-based event loop and comprehensive support for fundamental protocols such as HTTP, DNS, and TCP. JavaScript's existing popularity made Node.js accessible to the web-development community.

Industry support

There are thousands of open-source libraries for Node.js, most of which are hosted on the npm website. Multiple developer conferences and events are held that support the Node.js community, including NodeConf, Node Interactive, and Node Summit, as well as a number of regional events.

The open-source community has developed web frameworks to accelerate the development of applications. Such frameworks include Express.js, Socket.IO, Sails.js, Next.js and Meteor. Various packages have also been created for interfacing with other languages or runtime environments such as Microsoft .NET.

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. Some online IDEs also support Node.js, such as Codeanywhere, Eclipse Che, Cloud9 IDE and the visual flow editor in Node-RED.

Node.js is supported across a number of cloud-hosting platforms such as Jelastic, Google Cloud Platform, AWS Elastic Beanstalk, Azure Web Apps and Joyent.

Releases

Major Node.js versions currently enter Current release status for six months. Historically, up to Node.js 26, odd-numbered releases became unsupported after six months, while even-numbered releases moved to Active LTS. Starting with Node.js 27, Node.js is moving to an annual major-release cycle, and every major version is planned to move to LTS after its Current phase and an additional Alpha phase. LTS releases are generally supported for about 30 months, including Active LTS and Maintenance LTS periods. Production applications are recommended to use Active LTS or Maintenance LTS releases.

Technical details

Node.js is a JavaScript runtime environment that processes incoming requests in a loop, called the event loop.

Internals

Node.js uses libuv under the hood to handle asynchronous events. Libuv is an abstraction layer for network and file system functionality on both Windows and POSIX-based systems such as Linux, macOS, OSS on NonStop, and Unix. Node.js relies on nghttp2 for HTTP support. As of version 20, Node.js uses the ada library which provides up-to-date WHATWG URL compliance. As of version 19.5, Node.js uses the simdutf library for fast Unicode validation and transcoding. As of version 21.3, Node.js uses the simdjson library for fast JSON parsing.

Threading

Node.js operates on a single-thread event loop, 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 among all the requests that use the observer pattern is intended for building highly concurrent applications, where any function performing I/O must use a callback. To accommodate the single-threaded event loop, Node.js uses the libuv library—which, in turn, uses a fixed-sized thread pool that handles some of the non-blocking asynchronous I/O operations.

A thread pool handles the execution of parallel tasks in Node.js. The main thread function call posts tasks to the shared task queue, which threads in the thread pool pull and execute. Inherently non-blocking system functions such as networking translate to kernel-side non-blocking sockets, while inherently blocking system functions such as file I/O run in a blocking way on their own threads. When a thread in the thread pool completes a task, it informs the main thread of this, which in turn, wakes up and executes the registered callback.

A downside of this single-threaded approach is that Node.js does not 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. The server operating system (OS) is likely to distribute these threads across multiple cores. Another problem is that long-lasting computations and other CPU-bound tasks freeze the entire event-loop until completion.

V8

V8 is the JavaScript execution engine which was initially built for Google Chrome. It was then open-sourced by Google in 2008. Written in C++, V8 compiles JavaScript source code to native machine code at runtime. As of 2016, it also includes Ignition, a bytecode interpreter.

Package management

npm is the pre-installed package manager for the Node.js server platform. It installs Node.js programs from the npm registry, organizing the installation and management of third-party Node.js programs.

Event loop

Node.js registers with the operating system so the OS notifies it of asynchronous I/O events such as new connections. Within the Node.js runtime, events trigger callbacks and each connection is handled as a small heap allocation. Traditionally, relatively heavyweight OS processes or threads handled each connection. Node.js uses an event loop for concurrent I/O, 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.

WebAssembly

Node.js supports WebAssembly and as of Node 14 has experimental support of WASI, the WebAssembly System Interface.

Native bindings

Node.js provides a way to create "add-ons" via a C-based API called N-API, which can be used to produce loadable (importable) .node modules from source code written in C/C++. The modules can be directly loaded into memory and executed from within JS environment as simple CommonJS modules. The implementation of the N-API relies on internal C/C++ Node.js and V8 objects requiring users to import (#include) Node.js specific headers into their native source code.

As the Node.js API is subject to breaking changes at a binary level, modules have to be built and shipped against specific Node.js versions to work properly. To address the issue, third parties have introduced open-sourced С/С++ wrappers on top of the API that partially alleviate the problem. They simplify interfaces, but as a side effect they may also introduce complexity which maintainers have to deal with. Even though the core functionality of Node.js resides in a JavaScript built-in library, modules written in C++ can be used to enhance capabilities and to improve performance of applications.

In order to produce such modules one needs to have an appropriate C++ compiler and necessary headers (the latter are typically shipped with Node.js itself), e.g., gcc, clang or MSVC++.

The N-API is similar to Java Native Interface. OpenHarmony and ArkTS also adopts N-API, with the internal implementation rewritten.

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 the administration of these projects to working groups or committees. The LTS group that 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.

In August 2017, a third of the TSC members resigned due to a dispute related to the project's code of conduct. They resigned after a vote failed to remove a member from the leadership group against whom multiple complaints had been filed.