Node.js is a cross-platform, open-source JavaScript runtime environment that can run on Windows, Linux, Unix, macOS, and more.

[9] Node.js was initially written by Ryan Dahl in 2009,[10] about 13 years after the introduction of the first server-side JavaScript environment, Netscape's LiveWire Pro Web.

[12] Dahl criticized the limited capability of Apache HTTP Server to handle many (10,000+) concurrent connections, as well as the dominant programming paradigm of sequential programming, in which applications could block entire processes or cause the creation of multiple execution stacks for simultaneous connections.

The goal was to enable a structure that would be more receptive to community input, including the updating of io.js with the latest Google V8 JavaScript engine releases, diverging from Node.js's approach at that time.

[25] By 2016, the io.js website recommended returning to Node.js and announced no further io.js releases, effectively ending the fork and solidifying the merger's success.

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

[35] The source code may also be built on similar operating systems that are not officially supported, such as NonStop OS[36] and Unix servers.

[17] Developers can create scalable servers without using threading by using a simplified model that uses callbacks to signal the completion of a task.

[17][page needed] Node.js connects the ease of a scripting language (JavaScript) with the power of Unix network programming.

[17] Node.js was built on top of Google's V8 JavaScript engine since it was open-sourced under the BSD license, and it contains comprehensive support for fundamental protocols such as HTTP, DNS and TCP.

[51] The LTS Working Group manages strategy and policy in collaboration with the Technical Steering Committee of the Node.js Foundation.

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.

[54] 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 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,[55] StrongLoop Process Manager,[56] or pm2.

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 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.

[60] 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.

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.

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.

Other current groups include Website, Streams, Build, Diagnostics, i18n, Evangelism, Docker, Addon API, Benchmarking, Post-mortem, Intl, Documentation, and Testing.