What is JavaScript? JavaScript (JS) is a lightweight, interpreted programming language with first-class functions. It is most well-known as the scripting language for Web pages, but it is also used in many non-browser environments such as Node.js. Key Features Dynamic typing — Variables can hold any type of value. Prototype-based — Objects can inherit from other objects directly. First-class functions — Functions are treated like any other variable. Your First Program Run this in your browser console (F12) or in Node.js terminal. That's it — you wrote JavaScript! Summary JavaScript is the language of the web. Every modern browser can run it without any setup. In the next post we will write our first interactive program.