Node.js is a runtime environment that allows you to execute JavaScript on the server side. It is built on top of the V8 JavaScript engine, which is developed by Google and written in C++. V8 is a high-performance JavaScript engine that is designed to execute JavaScript code quickly and efficiently.

Node.js also makes use of the libuv library, which is written in C and provides an abstracted interface for various asynchronous operations.

libuv is written in C. It is a low-level library that provides a platform-agnostic interface for asynchronous I/O and other operations.

The libuv library is designed to be portable and can be used on a wide range of operating systems, including Windows, MacOS, Linux, and various Unix-like systems. It is written in C and uses a number of platform-specific APIs and libraries to provide the necessary functionality for each operating system. libuv is a multi-platform support library with a focus on asynchronous I/O. It was primarily developed for use in Node.js, but it is also used by other software projects.

libuv provides an abstracted interface for various asynchronous operations, such as file system access, network communication, and child process management. It abstracts away the differences between various operating systems and provides a consistent interface for these operations.

In Node.js, libuv is used to handle non-blocking I/O operations and to provide the event loop that powers the Node.js runtime. It is responsible for managing the execution of asynchronous callbacks, as well as for providing other core functionality such as timers, signals, and threadpools.

Overall, libuv is an important part of the Node.js runtime and plays a critical role in enabling the asynchronous, event-driven architecture that makes Node.js so efficient and scalable.

Together, V8 and libuv form the core of the Node.js runtime. V8 provides the JavaScript execution environment, while libuv handles non-blocking I/O and other asynchronous operations. This enables Node.js to provide a powerful and efficient runtime for building server-side applications and real-time applications.