What is JavaScript?
JavaScript is a dynamic, interpreted and weakly typed programming language which was built with the purpose of running in host environments (e.g. inside of a webpage in the browser).
It's part of pretty much any page you visit in the web as it's the only "thing" in web development that allows you (= the developer) to change something on the page at runtime. Basically everytime something opens, closes, moves or changes on a webpage, JavaScript will be involved.
There also a lot of webpages which are almost entirely powered by JavaScript (i.e. where a lot of the rendering work happens in the browser) - those pages typically use frameworks like Angular, but that's a topic we'll cover later in the course. :-)