JavaScript is a text-based programming language. It is used on the server-side and client-side to make interactive pages. Unlike HTML and CSS, which are concerned with page structure, JavaScript is used to create interactive elements.
In the context of a DAP, JavaScript is required to build the overlaid interface (the experience layer) that guides and helps users. By coding smart tips, tours, guides, or notifications over software, JavaScript allows users to become oriented and familiar with new applications or products.