Node.js

Node.js is an open-source JavaScript runtime environment. It runs JavaScript code outside of a web browser, allowing web developers to use JavaScript as the back-end of their web applications. Node.js is also cross-platform and runs on Windows, Unix, Linux, and macOS.

Before the introduction of Node.js, JavaScript could only run within a web browser. Websites could use JavaScript to add client-side interactivity on web pages and web applications, but the web server itself needed to use another language, like PHP, for its share of the work. Node.js allows JavaScript code to run server-side, which means that web developers can use one language for both the front- and backend of their web apps.

Node.js is popular among web developers for several reasons. First, it is efficient for applications that require many simultaneous connections, and can handle many requests at once. It also has a large ecosystem of open-source packages and libraries available through Node Package Manager, which allows developers to easily add new features by integrating existing modules into their applications. Finally, the ability to use one programming language instead of two reduces the complexity of a project and provides an easier learning curve.

NOTE: Node.js uses Google's V8 JavaScript runtime engine, the same engine used by the Chrome web browser.