What is JavaScript?

JavaScript is a dynamic computer programming language. (1)

JavaScript is a programming language that is one of the core technologies of the World Wide Web, alongside HTML and CSS.
As of 2022, 98% of websites use JavaScript on the client side for webpage behavior, often incorporating third-party libraries. All major web browsers have a dedicated JavaScript engine to execute the code on users' devices. (2)

JavaScript (JS) is a lightweight, interpreted, or just-in-time compiled programming language with first-class functions. (3)

According to MDN, in another definition, JavaScript is a programming language that allows you to implement complex things on web pages.

Every time a web page does more than just sit there and display static information for you to look at—displaying timely content updates, interactive maps, animated 2D/3D graphics, scrolling video jukeboxes, or more—you can bet that JavaScript is probably involved. (4)

JavaScript is a high-level, often just-in-time compiled language that conforms to the ECMAScript standard.[10] It has dynamic typing, prototype-based object-orientation, and first-class functions. It is multi-paradigm, supporting event-driven, functional, and imperative programming styles. It has application programming interfaces (APIs) for working with text, dates, regular expressions, standard data structures, and the Document Object Model (DOM). (5)